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SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUSLARVAE AND PREDACEOUS ARTHROPODS AND SIMULATED
DEFOLIATOR DAMAGE TO PEANUTS
ByJOHN ROBERT MANGOLD
A DISSERTATION PRESENTED TOUNIVERSITY
N PARTIAL FULFILLMENT OF THEOF DOCTOR OF
UNIVERSITY
THE GRADUATE COUNCIL OF THEOF FLORIDAREQUIREMENTS FOR THE DEGREEPHILOSOPHY
OF FLORIDA
1979
ACKNOWLEDGEMENTS
The author wishes to acknowledge his sincere apprecia-
tion to Dr. S. L. Poe, research advisor and chairman, for
his patience and assistance throughout the course of this
study. Special appreciation is extended to the supervisory
committee, Drs. J. W. Jones, C. A. Musgrave, D. H. Habeck,
and C. S. Barfield for advice and critical reviews of the
dissertation
.
The author wishes to express his gratitude to the
Department of Entomology and Nematology and in particular
to Stephanie Burgess, Gail Childs, Micky Ilartnett, Donna
Labella, Mike Linker, Carol Lippicott, John O'Bannon, Randy
Stoutt, and John Wood for help with field work.
The author also wishes to thank Dr. Habeck for identif
cation of lepidopterous larvae, Skip (Paul) Choate for
identification of Caribidae, and Roger Hetzman for identifi
cation of Geometridae.
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ii
LIST OF TABLES ^
LIST OF FIGURES •
ABSTRACT '^iii
INTRODUCTION 1
LITERATURE REVIEW 5
Foliage Consuming Lepidopterous Pests 5
Predaceous Arthropods Associated with Peanuts ... 9
Spatial Distributions of Arthropods 9
Effects of Defoliation on Plant Growth and yield. .H
SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE'
IN NORTH CENTRAL FLORIDA PEANUTS 1976-1978 21
Introduction 21
Materials and Methods 22
Results and Discussion 23
SEASONAL DYNAMICS OF PREDACEOUS ARTHROPODS IN NORTHCENTRAL FLORIDA PEANUTS 1976-1978 56
Introduction 56
Materials and Methods 57
Results and Discussion 58
SPATIAL DISTRIBUTION OF DEFOLIATING LEPIDOPTEROUSLARVAE ON PEANUTS 72
Introduction 72
Materials and Methods 73
Results and Discussion 74
EFFECTS OF UNIFORM HAND DEFOLIATION OF PEANUTS ONPLANT GROWTH 78
Introduction 78
Materials and MethodsResults and Discussion
iii
APPENDIX
LITERATURE CITED
BIOGRAPHICAL SKETCH
LIST OF TABLES
Table
1. Characteristics of peanut fields used in
survey, Alachua County, Florida , 1976-1978 30
2. Relative abundance of lepidopterous larvaeassociated with Alachua County, Florida,'Florunner' peanuts 1976-1978 31
3. Relative abundance of predaceous arthropodsassociated with Alachua County, Florida,•Florunner' peanuts 1976-1978 66
4. Correlation coefficients between lepidopterousfoliage feeding larvae and predaceous arthro-pods on Alachua County 'Florunner' peanuts 67
5. Percentage fit of counts of foliage consuminglepidopterous larvae to expected frequencydistributions, 1976-1978 76
6. Average percent light interception of intactand defoliated 'Florunner' peanut canopiesafter defoliation .
88
7. Regression equations of pod and crop weightsof intact and defoliated 'Florunner' peanutcanopies ^9
8. Specific leaf weight (SLW) of peanut leavesfrom intact and defoliated 'Florunner'peanut canopies in relation to weeks afterplanting 90
9. Effect of defoliation of 8 week-old 'Florunner'peanut plants on plant parts, 2 weeks post-treatment 91
10. Effect of defoliation of 'Florunner' peanutplants on plant parts at 19 weeks 92
11. Dry weight of leaves from intact and defoliated'Florunner' peanut plants 2 weeks after defol-iation 93
12. Solar radiation, temperature, rainfall andirrigation during growing season, 1978 98
V
LIST OF FIGURES
Figure Page
1. Location of Alachua County , Florida, peanutfields sampled in survey of peanut arthropods,1976-1978 33
2. Mean' numbers of FAW , CEW , and VBC larvaesampled from Alachua County, Florida, peanuts1976-1978. Breaks in lines indicate datesof insecticide application
3. Mean numbers of FAW larvae sampled fromAlachua County, Florida, 'Florunner' peanuts,1976-1978
4. Mean numbers of CEW larvae sampled fromAlachua County, Florida, ' Florunner ' peanuts,1976-1978 45
5. Mean numbers of VBC larvae sampled from
Alachua County, Florida, ' Florunner ' peanuts,1976-1978. .
". 47
6. Mean numbers of VBC, FAW. and CEW larvaesampled from various age of Alachua County,Florida, 'Florunner' peanuts, 1976-1978
7. Mean numbers of Plusiinae looper larvaesampled from Alachua County, Florida, 'Florunner'peanuts, 1976-1978
8. Mean numbers of GCW larvae sampled from AlachuaCounty, Florida, 'Florunner' peanuts, 1976-1978. ... 53
9. Mean numbers of BAW larvae sampled from AlachuaCounty, Florida, 'Florunner' peanuts, 1976-1978. ... 55
10. Mean numbers of ants, spiders, and L. ripariasampled from Alachua County, Florida, 'Florunner'peanuts, 1976-1978 69
11. Mean numbers of Geocor is spp., nabids, and 0.
insidiosus adults sampled from Alachua County,Florida, 'Florunner' peanuts, 1976-1978 71
vi
Figure Page
12. Quadratic regression of percent light inter-ception to LAI of defoliated and intact peanutcanopies, ** significant at 'v =0.01 level,and * significant at rT=0.05 level 95
13. Dry matter accumulation in peanut plant partsin relation to weeks after defoliation. Podweight is adjusted by factor of 1.88 X kernelweight 97
vii
Abstract of Dissertation Presented to the Graduate Councilof the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
SEASONAL ABUNDANCE OF DEFOLIATING LEPIDOPTEROUS LARVAE ANDPREDACEOUS ARTHROPODS AND SIMULATED
DEFOLIATION DAMAGE TO PEANUTS
By
John Robert Mangold
December, 1979
Chairman: Sidney L. PoeMajor Department: Entomology and Nematology
A survey of lepidopterous larvae on north central Florida
peanuts detected 27 species during 1976-1978. The most abun-
dant larvae were velvetbean caterpillar, Ant icarsia gemmatalis
(Hubner), fall armyworm, Spodoptera f rugiperda (J. E. Smith),
corn earworm, Heliothis zea (Boddie), Plusiinae loopers,
granulate cutworm, Felt ia subterranea (Fabricius) , and beet
armyworm Spodoptera exigua (Hubner). Only the former 3 species
of larvae reached damaging levels.
Fall armyworm larvae were most abundant during mid-July
to early August when peanuts were 12-17 weeks old. Corn ear-
worm larvae were most numerous in mid-July when peanuts were
ca. 12 weeks old. During August through early October velvet-
bean caterpillar larvae were most abundant on peanuts 15-17
weeks old.
The most abundant and important predators surveyed
in peanuts were ants, spiders, Labidura r ipar ia (Pallas),
viii
Geocoris spp. nabids, Orius insidiosus , and ground beetles.
Ants were abundant and probably important predators through-
out the season. Spiders were common predators for the entire
season. Labidura riparia numbers increased rapidly during the
season to greatest numbers at the season's end. Geocoris spp.
and nabids were abundant from mid-August to September then
declined in number late in the season. Peak abundance of
0. insidiosus occurred during mid-June and early July, then
declined sharply.
Correlation coefficients between predators and foliage
feeding larvae indicated nabid abundance was closely associ-
ated with velvetbean caterpillar numbers. Spiders, L. riparia,
Geocoris spp. and 0. insidiosus were also associated with
larval numbers.
The spatial distributions of fall armyworm, corn earworm,
velvetbean caterpillar, Plusiinae loopers, and granulate cut-
worm were fit to 6 frequency distribution models. The common
k values calculated for the 5 species were 3.93, 5.20, 7.27,
2.57, and 3.58 respectively. Only the first 2 common k
2values significantly fit (P==0.05) a test for homogenity
of k.
Uniform hand defoliation of peanut canopies at 4 levels
reduced yield of peanuts. Increases in specific leaf weight
and decreases in light interception of defoliated canopies
were recorded. Quadratic regressions of light interception
as a function of leaf area index were calculated for defoli-
atai and intact canopies. Plants defoliated 75% at 8 and 11
weeks after planting compensated for defoliation by growing
ix
significantly more leaves than undefoliated plants. Plants
defoliated 75% at 8 weeks also decreased stem growth. De-
foliation also reduced crop and pod growth rates of defoli-
ated plants compared to undefoliated plants.
X
INTRODUCTION
The increasing world population has focused our atten-
tion on high protein food plants among which is Arachis
hypogea L., the groundnut or peanut. Leading producers of
peanuts by acreage are: India 35%, China 15%, United States
8%, Nigeria 8%, and Senegal 7% (Janick et al . 1974).
Approximately 650,000 ha of peanuts are produced annually
in the United States. Peanuts rank ninth in acreage among
major field crops and second in dollar value per acre in
the United States (McGill et al . 1974). The distribution
of peanut acreage allotments in the United States is:
Georgia 33%, Texas 23%, Alabama 14%, North Carolina 11%,
Oklahoma 9%, Virginia 7%, Florida 4%, and South Carolina 1%
(McGill et al. 1974).
Peanuts are one of many crops in Florida's diversified
agriculture. The Florida peanut acreage is ca. 22,270 ha
of which 3,080 ha are in the state's north central peanut
growing belt centered in Alachua, Levy, and Marion Counties
(USDA 1977).
Most insecticide applications on peanuts in the south-
eastern United States are made to control foliage consuming
lepidopterous larvae (French 1973). Pilot pest management
programs have demonstrated that insecticide usage can be
1
2
substantially reduced with weekly population assessment and
economic thresholds as a guideline for insecticide applica-
tion (French 1975), The economic thresholds currently in
use are based on limited data from defoliation experiments,
larval consumption data, and principally on experience.
Among the first steps toward the implementation of a
pest management program are the determination of the insect
pest species present in peanut fields and the evaluation of
their effect upon the crop. In the United States the peanut
pest complex varies with locality necessitating regional
surveys. A knowledge of the regular, occasional, and poten-
tial pests in a particular area is necessary before steps
can be taken to control them with timely usage of insecti-
cide .
The seasonal dynamics of defoliating 1 epidopterous
insects on peanuts in Florida has not been documented.
Seasonal occurrence information for populations described
in the literature from other states is based primarily on
experience and not on long term studies. Data relating
plant age to numbers of foliage feeding larvae have not been
published, but are necessary for determining which plant
ages should be critically studied in relation to defoliation.
Foliage consuming larvae considered important in the
southeastern United States include fall armyworm, Spodoptera
f rugiperda (J. E. Smith), corn earworm, Hel iothis zea Boddie,
velvetbean caterpillar, Anticarsia gemmatalis Hubner, granu-
late cutworm. Felt i.-3 subterranea (Fabricius), and beet army-
worm, Spodoptera exigua (Ilubner) (Bass and Arant 1973).
3
The use of natural control agents such as predators and
parasites is ideally maximized in a pest management program.
The parasite complex of lepidopterous larvae on Florida
peanuts has previously been discussed (Nickle 1977) however,
no description of the predaceous arthropod complex on peanuts
in the southeastern United States has been reported. Any
understanding of the biotic potential of both major and
minor pests is impossible without an analysis of the predator
complex in the crop.
Better quantification of the relationship of defoliation
to yield loss is needed to further define defoliation levels
at which treatments are needed. A systems approach to peanut
plant growth and development as affected by defoliation is
being pursued to develop models that can realistically simu-
late the dynamic nature of insect defoliation and plant
growth (Barfield and Jones 1979). Most previous defoliation
experiments have emphasized defoliation effects on final
yields, but ignored how defoliation caused the observed
effect. Confounding environmental effects such as drought
stress and the presence of other pests such as Cercospora
leafspot have often made defoliation experiments less
meaningful
.
The objectives of the research reported here were to:
1. describe the seasonal occurrence of foliageconsuming lepidopterous larvae on peanuts in
north central Florida
2. determine the seasonal occurrence of predaceousarthropods in north central Florida peanuts
4
3. determine the spatialfeeding lepidopterous
4. examine the effect ofdamage on peanuts usi
distribution of foliagelarvae on Florida peanuts
simulated defoliatorg plant growth analysis
LITERATURE REVIEW
Foliage Consuming Lepidopterous Pests
The arthropod fauna associated with peanuts in the United
States is composed of endemic and introduced species that
have adapted secondarily to this plant of South American
origin. Thus, as a rule, arthropods infesting peanuts in
North America are not specialized feeders, and their relative
importance as peanut pests often is in inverse correlation
to the availability of alternate preferred hosts.
The peanut plant is damaged by a variety of arthropod
pests in the United States. In the southeastern peanut belt
most insecticide applications are made to control foliage
feeding lepidopterous larvae (French 1973). Typically insec-
ticides are applied 0-4 times per field to kill foliage
feeding larvae. Foliage feeding larvae of major economic
significance in the Southeast include fall armyworm,
Spodoptera f rugiperda (J. E. Smith), corn earworm, Heliothis
zea (Boddie), velvetbean caterpillar, Anticarsia gemmatalis
(Hubner), and granulate cutworm, Feltia subterranea (Fabricius)
Other arthropods of major economic importance in Florida
include lesser cornstalk borer, Elasmopalpus lignosellus
(Zeller) and spider mites.
6
The fall armyworm is a periodic defoliator of peanuts
in the southeast. Some feeding damage occurs every year
and frequently sufficient number of larvae are present
to completely defoliate plants in outbreak years (Bass and
Arant 1973). Consequently, severe damage to peanuts in
southeastern Alabama and southwestern Georgia has been
reported (Arant 1948a). In Oklahoma, fall armyworm was
reported numerous in some areas on peanuts during October,
but damaging populations were not common in 1972-1974
(Wall and Berberet 1975).
The corn earworm usually causes light to moderate
damage. Occasionally severe infestations occur and complete
defoliation of plants occurs (Bass and Arant 1973). In a
2 year study in Georgia, Leuck et al . (1967) found indices
of foliage ragging by corn earworm damage were negatively
correlated with yield. Morgan (1979) reported corn earworms
were most damaging during early August in Georgia. Wall and
Berberet (1975) found corn earworm was one of the 2 most
common foliage feeders collected in Oklahoma. The corn
earworm is the most common insect defoliator on peanuts in
the West Cross Timbers area of Texas although populations
usually are not economically damaging (Sears and Smith 1975).
The velvetbean caterpillar also causes damage to
peanuts every year in Alabama, Florida, and Georgia (Bass
and Arant 1973). Damaging populations of velvetbean cater-
pillars are not common in Oklahoma although larvae may become
numerous in October (Wall and Berberet 1975). Velvetbean
7
caterpillar is one of the few peanut defoliators that have
been experimentally proven to significantly reduce yields.
English (1946) applied insecticides for velvetbean cater-
pillar populations in Alabama and reported 9-65% yield
reductions in untreated plots. Arant (1948b) demonstrated
that velvetbean caterpillar defoliation caused 20-43% yield
losses from untreated Alabama peanuts.
The granulate cutworm damages peanuts by feeding on
foliage and underground parts. When infestations are severe,
portions of leaves and stems may bo cut from the plants.
In Georgia damaging infestations may occur from late June
until early August, but are most frequent about mid July
when as many as 11 larvae per row foot may be present (Morgan
and French 1971). Three generations of granulate cutworm
on peanuts have been recorded from Georgia (Bass and Johnson
1978). Cutworm populations peak in late June, late July,
and again in late August: the last generation is usually the
most noticeable and damaging.
The beet armyworm, Spodoptera exigua (Hubner) is a
minor foliage feeding pest that infrequently causes damage.
A few instances of serious defoliation have been reported
(Bass and Arant 1973).
Larvae of the rednecked peanutworm, Stegasta bosqueel 1 a
(Chambers) may cause minor damage (Bass and Arant 1973).
Feeding is confined to unopened leaves and the meristematic
region of buds and thus larvae may retard terminal growth
(Arthur et al. 1959). The rednecked peanutworm is the most
8
common insect pest of peanuts in Oklahoma (Wall and Berberet
1979). Walton and Matlock (1959) obtained significantly
higher yields through use of chemical controls for this pest
in Oklahoma, but Arthur et al . (1959) and Bissell (1941)
reported that control of this pest did not increase yields
in Alabama and Georgia, respectively.
A number of other foliage feeding larvae have been
associated with peanuts. These potentially injurious in-
sects include: the tobacco budworm, Hel iothis virescens
(Fabricius); yellowstriped armyworm, Spodoptera ornithogall
i
(Guenee); the saltmarsh caterpillar. Est igmene acrea (Drury);
the yellow wollybear, Pi acris i a virginica (Fabricius); green
clovorworm, Plathypena scabra (Fabricius); cabbage looper,
Trichoplusia n
j
(Hubner); soybean looper, Pseudoplusia
includens (Walker); cotton square borer, Strymon mel inus
(Hubner); Platynota nigrocerri na Walsingham; and Argyrogramma
verucca (Fabricius) (Kimball 1965, Canderday and Arant 1966,
Tietz 1972, Wall and Berberet 1975, Smith and Jackson 1976,
Martin 1976).
There is a paucity of published information on the
seasonal abundance of foliage feeding larvae. Sears and
Smith (1975) developed a partial monthly life table for corn
earworm on Texas peanuts. Greatest larva] numbers occurred
during July. Weekly averages of foliage feeding larvae in
1972 for 4 Georgia peanut fields were reported by French
(1974). Granulate cutworms, corn earworms , and fall armyworms
comprised 77% of the larvae sampled, but seasonal fluctua-
tions for individual species were not given.
9
Predaceous Arthropods Associated with Peanuts
Knowledge of the seasonal and relative abundance of
predaceous arthropods is helpful in defining their role in
regulating pests of peanuts. With the exception of a
report of striped earwigs, Labidura riparis (Pallas)
collected in pitfall traps in Florida peanuts (Travis 1977),
there have been no studies of seasonal incidence or relative
abundance of predators in peanuts. Martin (1976) found
Coleomegilla maculata (De Geer) and Geocoris punctipes (Say)
the most numerous predators in small peanut plots in north
Florida; and spiders were present in low densities.
Predaceous insects most commonly found in Texas peanut
fields are lady bugs, assassin bugs, lace-wings, ground
beetles, predaceous stink bugs, Geocoris spp., Nabis , Orius,
and praying mantids (Smith and Hoelscher 1975). Spiders
were one of the more numerous predators sampled in a study
of the effect of insecticide placement on nontarget organ-
isms in Texas peanuts in 1972-1973 (Smith and Jackson 1976).
Spatial Distributions of Arthropods
The method of sampling for foliage feeding lepidoptera
larvae has been manual shaking of plant branches onto a ground
cloth similar to the method of sampling soybeans developed by
Boyer and Dumas (1963). The foliage shaking sample method has
been used extensively in Georgia, Florida, Alabama, and Texas
and economic thresholds are based on sampling results obtained
with it. In North Carolina a standard sweep net is recom-
mended for population estimation (Stinner et al . 1979).
10
Recent emphasis on accurate sampling procedures for
insects in peanuts has revealed the need for better defini-
tion of the spatial distribution of these insects. Also,
knowledge of spatial patterns provides insight into the
biology of the species in question. Data on the spatial dis-
tribution of insects is necessary before development of se-
quential sampling schemes may be effected (Waters 1955).
Spatial distribution models are probability distribu-
tions that relate the frequency of occurrence of an event,
depending on the mean of the measurements and in some cases
on one or more parameters.
The most useful statistical distributions in entomo-
logical research have been the Poisson and negative binomial
(Southwood 1978). The Poisson distribution describes a
random distribution with variance equal to the mean. In
insect sampling the variance most commonly will be larger
than the mean, indicating that the distribution is aggre-
gated or clumped. The most useful distribution describing
a clumped insect population has been the negative binomial.
The versatility of this distribution arises from the fact
that it may arise from at least 5 different models (Waters
and Henson 1959).
The probabilities of a Poisson distribution are given
by- /V X
P = g ^ /-^ x = 0, 1, 2, . . .,
X X'!
where P is the expected proportion in the xth class and
X = 0 , 1 , 2 , . . . is the value of a discrete random variable.
11
The mean and variance of the distribution are equal toyU.
The usual procedure is to make a number of observations and
The negative binomial is defined by 2 parameters, the
mean and a positive exponent k. The distribution is gen-
erally expressed by the expansion of
With increasing randomness, the variance of the distribution
approaches the mean and the Poisson more accurately describes
the distribution.
Effects of Defoliation on Peanut Plant Growth and Yield
Typically, peanuts in Florida are planted from early
April to late May; in exceptional years spring droughts delay
some planting until June. 'Florunner' , released in 1969,
is the most widely grown peanut cultivar in the United States.
Over 80% of the peanuts grown in Florida are 'Florunner'.
Peanuts exhibit an indeterminate growth pattern. The
plant growth of 'Florunner' is prostrate with the typical
sequential branching pattern of Virginia type varieties
—
i.e. alternate pairs of reproductive and vegetative nodes
on laterals and no reproductive nodes on main stems.
'Florunner' peanuts grown under normal conditions in
Florida begin flowering at ca. 30 days after planting; peak
the mean of these, x, provides an estimate of ytLand
(q-p) ^ where k> 0 , p= ,and q= 1 + p.
The expansion of the probability is given by
X = 0,1,2
12
flowering occurs at 60 days. After 80 days flowers are no
longer present (McCloud 1974, McGraw 1977). The seasonal
flowering pattern has a frequency curve similar to a normal
distribution. Pegs begin to appear ca. 7-14 days after
flowering. Generally only 15-307o of the flowers produce
mature pods (Smith 1954). Early pegs generally produce a
higher proportion of fruit than pegs initiated later. Usually
by 56 days after planting the first pegs begin to swell into
pods. Pod number per plant increases steadily until ca. 84
days at which time the pod load stabilizes. By day 70, seeds
begin filling. Pod formation is completed soon after the
full pod load is established and growth thereafter is in the
seed (Duncan et al . 1978). The pegs and pods which fail to
mature remain attached to the plant and are not eliminated
by abscission (Smith 1954).
McGraw (1977) used plant growth analysis to describe
'Florunner' growth as follows: Plant growth followed a
sigmoid curve. The first 7 weeks of vegetative growth was
geometric. All assimilates were used for accumulation of
dry matter into vegetative parts. The largest component in
terms of dry matter during this phase was the leaf component.
There was a linear growth phase which extended from week 7
to week 16. At 10 weeks plant development shifted from
vegetative to reproductive growth and the rate of dry
matter production began to slow since more photosynthate
production was required for seed production than vegetative
matter. Dry matter accumulation in the stem and leaf compon-
ent ceased at about 84 days. The pods filled at a linear
rate until maximum dry weight was reached at day 133.
13
Duncan et al. (1978) calculated the crop growth rate
of 'Florunner' from the same data used by McGraw. Linear
regression of crop dry weights from canopy closure at 55
days until seed growth became significant at 70 days deter-
2mined that the crop growth rate was 21.2g/m /day. This was
assumed to be the period of maximum crop growth rate.
Partitioning was used by Duncan et al. (1978) to
refer to the division of daily assimilate between reproduc-
tive and vegetative plant parts. The partitioning factor
may be calculated by comparing the fruit and vegetative
growth rates. A correction is made for the fruit growth
rate to account for the additional energy expenditure of
seed production. Correction factors developed by Hanson
et al. (1961) and Penning de Vries (1974) are used to
compensate for the higher concentration of oils and proteins
in seeds. Duncan et al . (1978) estimated partitioning by 2
methods for 'Florunner'. From comparison of crop and
corrected fruit growth rates the reproductive partitioning
factor was calculated as 84.7%. The value for the repro-
ductive partitioning factor estimated from simulations of
the PENUTZ model was 72% (Duncan et al. 1978).
Two useful terms often used to describe plant canopies
are leaf area index (LAI) and percent ground cover. Percent
ground cover is the percent of soil surface that is covered
by the crop canopy. The LAI is defined as leaf area per
unit of ground area and does not indicate directly the
amount of solar radiation intercepted by the canopy. Larval
14
consumption rates of leaf tissue can, however, be easily
coupled to LAI. Measurement of percent light interception
and LAI of canopies are both needed for describing the
structure of defoliated and intact canopies. For example, ^Rudd et al. (1979) used the light interception— LAI relation-
ship of soybean. Glycine max L. (Merr.) determined by Shibles
and Weber (1965) to model soybean insect defoliation in a
dynamic model of soybean growth and yield.
McGraw (1977) found that ground cover of peanuts
increased geometrically from 10% at 3 weeks to 100% at 8
weeks after planting and remained 100% until harvest. The
LAI increased from 0.11 at 3 weeks to 1.5 at 7 weeks. At
8 and 10 weeks the LAI had reached 3.6 and 5.6, respc;ct ively
.
After 10 weeks the LAI maintained an average of 5.6 for 5
weeks until Cercospora leaf spot partially defoliated the
canopy
.
There have been several reported defoliation experiments
of various varieties of peanuts with very inconsistent yield
reductions (King et al. 1961, Greene and Gorbet 1973, Enyi
1975, Williams et al . 1976, Campbell unpubl"!", Nickle 1977).
Results generally demonstrate that defoliation at early pod-
fill, 8-12 weeks after planting, causes the most serious
yield losses.
King et al . (1961) simulated defoliator damage by
mechanical removal of leaf canopy from the top 1/3 - 2/3 's
^Dr. W. V. Campbell, professor of entomology, North CarolinaState University, Raleigh.
15
of irrigated and dryland peanuts in Texas. Seventy-five
percent defoliation of 56-day-old plants and 50% defolia-
tion of 75-day-old plants did not affect yields of irrigated
peanuts. Thirty-three percent defoliation did not signifi-
cantly reduce yields of 53- and 94-day-old plants, but
higher defoliation levels did reduce yield of dryland
peanuts
.
A mowing machine was used by Greene and Gorbet (1973)
in a 3 year study to approximate 5 levels of defoliation of
'Florunner' peanuts in Florida. Removal of ca. 33% of leaf
area reduced yields at most growth stages; yield was reduced
more when defoliation was delayed. Yield losses ranged
from 1.8-7.4%, 3.7-32%, 8.6-44% and 34-63% for defoliation
levels of 10-15, 20, 33, and 50%, respectively. Some repro-
ductive branches and pegs were removed at the 507o defolia-
tion level.
Enyi (1975) hand defoliated 'Dodoma' edible peanuts at
2 week intervals at 3 levels in Tanzania. Defoliation levels
of 50 and 100% reduced pod and stem weight, and kernel size.
Greatest yield losses occurred to plants defoliated ca. 1
week after early podding stage. It appeared that defolia-
tion reduced pod number by slowing stem growth which resulted
in a reduction in number of flowering nodes.
Williams ot al. ( 1976) det:ermined growth rates of plant
parts of 'Makulu Red' peanuts in Rhodesia. Defoliation
levels of 50 and 75% were achieved by removal of 2-3 leaflets
per tetraf foliate. Compared to the untreated check, defoliation
16
decrcrsed cro]) growth rate^ 2 weeks after defoliation
by 17-42%. Stem and pod growth rates were also decreased
by defoliation.
Campbell (unpubl.) used hand shears to clip leaves
from unirrigated peanuts in North Carolina. Yield reduc-
tions started with 50% defoliation on 15 July and 15 Septem-
ber, and 20% defoliation on 1 September, and 10% defolia-
tion on 1 and 15 August.
Unirrigated 'Florunner' peanuts were hand defoliated
at 5 levels at 2 locations in north central Florida (Nickle
1977). Yield reductions in both plots were most severe at
63 days after cracking. Yield reductions averaged 2-6.8,
7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75, and 100%
defoliation, respectively for the 2 defoliation experiments.
Peanut quality was also reduced by some defoliation treat-
ments .
Too often researchers have studied the effect of defol-
iation only in terms of the final harvest. Growth analysis
is a useful tool in the quantitative analysis of plant
growth. Generally 2 assessments are required to carry out
a simple growth analysis of plants with a closed canopy--
i.e., dry weights of plant material per unit area of ground
and LAI of the canopy (Radford 1967). Knowledge of the time
and rate of dry matter accumulation is vital to understanding
the physiology of any crop and is particularly amenable to
studying the effect of defoliation.
17
Previous defoliation studies have examined only the
effect of defoliation on final yield or limited growth
rate changes caused by defoliation. One of the few papers
reporting canopy characters and photosynthesis of defoliated
peanuts was that of Boote et al . (1980). Defoliation of 75%
of the upper 42% of the canopy leaf area of unirrigated
•Early Bunch' peanuts corresponded to 25% of the total
leaf area and reduced light interception from 95.6 to 74%.
Canopy carbon exchange rate was reduced 35% from 20.2 mg
o ? 14COg/dm /h to 13.1 mg C02/dm7h and uptake of was
reduced by 30%.
Nickle (1977) questioned the relevancy of manual
excision of peanut leaflets in establishing crop damage-
yield relationships, manual leaf removal was thought to be
more stressful than larval defoliation. However, Thomas
et al. (1979) demonstrated good agreement in yield losses
between manual soybean leaflet removal and defoliation by
caged cabbage looper, T. ni .
Removal of a fixed proportion of leaflets per tetra-
fioliate throughout the canopy has a further disadvantage
in that it may not realistically simulate the effect of
insect defoliation in terms of canopy damage site. The
early instars of soybean looper on soybeans are reported
to feed selectively on low-fiber containing leaf tissues of
terminal leaves. The later instar larvae feed on non-terminal
leaves (Kogan and Cope 1974). Similar observations of corn
earworm larval damage to peanuts were reported by Huffman
18
(1974) and Morgan (1979). The last 2 instars of noctuid
larvae consume 80-91% of the total consumed foliage (Snow
and Callahan 1968, Nickle 1977), Most researchers have
assumed terminal bud damage is minor compared to the much
greater potential loss of older foliage.
Surveys of foliage feeding larvae on peanuts in 1976
indicated that peanuts 11-19 weeks old were most often
attacked by defoliators (Mangold et al . 1977). Terminal
damage at this time is probably not of major significance
since the majority of leaf matter is present. Sustained
terminal bud damage to younger plants during the geometric
vegetative growth stage may be an important aspect of
defoliator damage by corn earworm and possibly fall army-
worm .
A systems approach to the effect of defoliation on
peanut growth and yield is being pursued (Barfield and Jones
1979). There are currently 3 peanut plant models. Two of
the models lack appropriate mechanisms for coupling defolia-
tion to peanut growth and development (Duncan 1974, Young
et al. 1979). The third model, by Smith and Kostka (1975)
is based on yield loss and larval consumption rates and is
not general enough for studying the dynamics of insect
defoliation on plant growth.
Based on limited dcT-foliation oxperiments, larval con-
sumption data, and principally on experience, an economic
threshold of 4 or more foliage feeding larvae per row foot
was used in a pilot pest management program in Georgia in
19
1972-1974 (French 1975). In 1974 the Georgia pilot program
reduced applications from an average of 2 per field for
defoliators to an average of 0.05 per field in the program's
114 fields. Sampling 7.6 m of row for defoliators by
shaking the branches and the empirical threshold were respon-
sible for the reduction in insecticide usage (French 1973).
In 1975 the Tri-States Pest Management Project was
initiated on corn, soybeans, and peanuts in Georgia, Alabama,
and Florida. Shake cloths were used to sample 0.91 m sections
of row for defoliators. An action threshold of 4 larvae per
row foot was used before early August but later increased
to 6 larvae per row foot after early August (Linker and
Johnson 1978).
In Texas, field observations and limited research data
indicate 3-5 and 6-8 medium to large larvae per row foot
can be tolerated before yield losses will occur on dryland
and irrigated Spanish peanuts, respectively (Hoelscher 1977).
Economic thresholds for defoliators on peanuts should
be revised. The concept of economic threshold is very use-
ful in the primitive state of the art. The economic threshold
refers to the pest population density at which active control
measures should be initiated to prevent the pest from reach-
ing the economic injury level. The economic injury level
is the lowest number of insects that will cause economic
damage. However, there are many factors that ideally should
determine an economic threshold. Beneficial insects, pest
pathogens, plant growth stage, interacting plant pathogens,
20
market prices, weather conditions, farming practices,
economics of crop production, pest species, etc., influence
the economic threshold. Economic thresholds are useful in
providing a guideline to the farmer as to whether it is
economical to control a pest
.
Defoliation studies indicate that plant age greatly
influences the amount of defoliation that can be tolerated
without yield loss. The static nature of current action
thresholds does not reflect the dynamics of the impact of
defoliation on crop yield. Also, studies on larval consump-
tion rates of peanut leaves demonstrate major differences
in relative amounts of foliage consumed among defoliators
(Snow and Callahan 1968, Nickle 1977, Huffman and Smith
1979). Future action thresholds should consider the balance
of defoliator species involved at the time.
SEASONAL DYNAMICS OF DEFOLIATING LEPIDOPTEROUS LARVAE IN
NORTH CENT-RAL FLORIDA PEANUTS 1976-1978
Introduct ion
In the southeastern United States most insecticide
applications on peanuts have historically been made to
control foliage consuming lepidopterous larvae (French
1973). Foliage feeding larvae reported reducing yields
in the southeastern United States include fall armyworm,
Spodoptera f rugiperda,
(J. E. Smith); corn earworm,
Heliothis zea (Boddie); velvetbean caterpillar, Anticarsia
gemmatalis (Hubner) ; and granulate cutworm, Feltia sub -
terranea (F. ) (Bass and Arant 1973).
Practically no information is published on the seasonal
occurrence of foliage consuming lepidopterous larvae on
peanuts. Sears and Smith (1975) developed a monthly life
table for corn earworm on Texas peanuts. Weekly averages
of foliage feeding larvae for 4 Georgia peanut fields in
1972 were reported by French (1973), however; seasonal
fluctuations of individual pest species were not given.
The seasonal occurrence of foliage feeding lepidopterous
larvae on peanuts in north central Florida was studied in
1976-1978 and the results are reported here.
21
22
Matei'ials and Methods
A total of 14 Alachua County, Florida, growers' fields
planted to 'Florunner' peanuts were surveyed during 1976-1978
for relative densities of lepidopterous larvae (Table 1).
Samples were taken at weekly intervals starting on 6 July,
15 June, and 23 June in 1976, 1977, and 1978, respectively,
and continued until harvest. A total of forty 0.91 m of row
samples were taken at each sample date by the ground cloth
method
.
Samples were taken by folding back the branches and
gently placing a ground cloth 0.91X0.91 m against plant
bases of one side of the row. The peanut canopy was beaten
downward vigorously with forearm and hands 6 to 8 times
over the cloth to dislodge arthropods. Arthropods that were
observed either under the branches while inserting the ground
cloth or on the ground cloth were identified, counted, and
recorded
.
In 1976-1977 samples were taken throughout each field
in a manner similar to that used by commercial scouts.
All areas of the field were sampled in a random manner with
not more than 10% of the samples within ca. 20 m of any
field edge. In 1978 samples were taken along the transects
of an X-shaped pattern which was aligned along the diagonals
of the field. Twenty samples per transect were taken every
tenth row in Field M and every thirteenth row in Field N.
Each week sampling began on a different row.
23
The fields surveyed in this study were all in Alachua
County in the vicinity of Archer, Florida (Fig. 1) on the
southern edge of the southeast peanut belt. Approximately
3,080 ha or 14% of Florida's peanut acreage is in north
central Florida. Vegetation surrounding the study sites
was mainly woods and pasture with limited acreages of field
corn and rarely soybeans.
Some of the fields surveyed were adjacent. The adja-
cent fields sampled were: (1) C and D; K and L; and B, I,
and J. Also Field E was located less than 1 km from I and J.
Results and Discussion
The following 27 species of lepidopterous larvae were
associated with Alachua County peanuts: Arctiidae: Dia-
crisia virginica (Fabricius) and Estigmene acrea (Drury)
;
Gelechiidae: Stegasta bosqueela ; Geometridae: Anavitrinella
pampinaria Guenee and Cyclophora serrulata (Packard)
;
Lycaenidae: Strymon melinus (Hubner); Noctuidae: Anicla
infecta (Ochsenheimer ) , Anticarsia gemmatalis ,Argyrogramma
verruca (Fabricius), Elaphria nucicolora (Guenee) Elaphria
grata Hubner, Feltia subterranea , Hel iothis virescens
(Fabricius), H. zea. Pseudaletia unipuncta (Haworth),
Pseudoplusia includens (Walker), Spodoptera eridania (Cramer),
S. exigua, S. dol ichos (Fabricius), S. f rugiperda , S.
latifascia (Walker), S. ornithogalli (Guenee), and Tricho -
plusia ni (Hubner); Pyralidae: Elasmopalpus lignosellus
(Zeller); Pieridae: Eurema lisa (Boisduval and Leconte); and
Tortricidae: Platynota f lavedana Clemens and Sparganothis
24
sulfureana (Clemens). The total numbers of less numerous
lepidopterous species were: 53 E. lignosellus , 15 E. acrea,
8 S. melinus , 6 S. bosqueela , 6 E. nucicolora , 5 A. pampinaria ,
4 E. grata , 3 A. infecta, 3 P. unipuncta , 3 E. lisa , 2 P.
f lavedana , 2 P. virginica , and 1 C. serrulata . S. sulfureana
larvae were collected only from buds and were not observed
in beat cloth samples.
Twelve of the 27 lepidoptera larvae associated with
peanuts are new records: A. infecta , A. pampinaria,
C. serrulata , E. lisa , E. grata , E. nucicolora , P. f lavedana,
P. unipuncta , S. sulfureana , S. dolichos , S. eridania , and
S. ornithogalli . With the exception of P. unipuncta , A.
infecta, and E. grata some larvae of the other 9 species
were reared to adults on peanut foliage.
Every year the 3 most abundant lepidopterous larvae
were velvetbean caterpillar, corn earworm, and fall armyworm
(Table 2). Plusiinae loopers were common in 1976 and 1978,
but not in 1977. Beet armyworm was more numerous in 1977
than in other years. Beet armyworms were also extremely
numerous on soybean seedlings in 1977 in Florida (Anon.
1977a, Anon. 1977b).
Population levels of fall armyworm (FAW) were highest,
reaching 17 per sample in Field H on 4 August, during mid -
July to early August in 1976 (Fig. 2). Field H was the only
field where FAW larvae were the major pest that required
treatment. In the other fields surveyed in 1976, fall army-
worm larvae peaked at 0.5-3.8 larvae per sample with the
25
exception of Fields C and D where 9 larvae per sample were
present the first week of August (Fig. 2). In 1977 larvae
began to be abundant in mid-June in Field K and reached
highest levels in Fields K and L in mid-July (Fig. 2). The
early June abundance of FAW larvae on peanuts in Field K
is probably an indication of the outbreak of FAW reported
throughout the Southeast in 1977. In 1978 population levels
of FAW were low, peaking at 0.6 larvae per sample and 3.1
larvae per sample on 20 July in Field M and Field N, respec-
tively .
Larvae of FAW were less numerous in 1978 than in 1976
and 1977 (Fig. 3). In fields not treated with insecticides
during July a natural decline of FAW larvae occurred during
early to mid-August. In no instances were FAW larvae
numerous after mid-August.
Rearing of Ileliothis spp. larvae on artificial diet
indicated ca. 95% of the Ileliothis in 1976-1977 were H. zea
(Nickle and Mangold, unpubl.). In 1976 the greatest numbers
of corn earworm (CEW) , 8.4 per sample, occurred in Field F
on 21 July (Fig. 3). The range of maximum densities in
other fields surveyed in 1976 was 0.6-4.6 per sample. In
1977 CEW attained very high levels of 19 per sample on 20
July in Field L (Fig. 3). The late planted Field L was
probably an exceptionally attractive oviposition site for
CEW moths because peak flowering occurred during early July
at a time when moths were emerging from field corn. Corn
earworm has demonstrated a preference for the flowering
26
stage of 4 of its major agricultural hosts in North Carolina
(Johnson et al . 1975). In 1978 CEW densities reached their
highest levels of 0.6 and 3.1 in mid-July in Fields M and
N, respectively.
The patterns of seasonal abundance of CEW for 1976-
1978 were very similar (Fig. 4). In all 3 years CEW larvae
were most numerous the third week of July. In fields not
treated with insecticides during July, a natural decline of
larvae occurred during late July. Corn earworm larvae were
never numerous after mid-August.
Velvetbean caterpillar (VBC) larvae were first detected
in peanut fields the second week of July. Velvetbean
caterpillar was the only pest that demonstrated resurgence
after insecticide application (Fields B, G, H, Fig. 2).
The dynamics of VBC resurgence appear very similar to the
resurgence of the same species observed on soybeans (Shepard
et al. 1977). In 1976 VBC larvae were most numerous in Field
G where 36 larvae per sample were counted on 8 September.
Very low numbers of larvae were present in the fields
planted early in April; maximum VBC densities ranged from
0.05-0.60 larvae per sample. Maximum larval densities
ranged from 0.7 to 7.1 per sample in Fields K and L,
respectively in 1977. Highest levels of VBC larvae in 1978
were 8.0 and 2.3 per sample in Fields M and N, respectively.
In 1977 VBC larvae increased in number ca. 2 weeks
later than in 1976 and 1978 (Fig. 5). In no instances were
27
VBC larvae present in numbers greater than 1 per sample
until August. Velvetbean caterpillar larvae were the only
numerous insect pest from mid-August through early October.
Adjacent fields of similar planting dates had similar
patterns of larval abundance in terms of timing and density
—
i.e. Fields C and D; and E, I and J. In the 2 cases where
planting dates of adjacent fields differed 4-5 weeks,
later planted fields had higher larval densities. The late
planted Field B, adjacent to Fields I and J, had 5 times
more velvetbean caterpillar the third week of August.
Similarly, the very late planted Field L had 8 times more
velvetbean caterpillar than the adjacent Field K on 2
September. Also corn earworm numbers were 4 times greater
in Field L than Field K on 20 July. Therefore, planting early
in north central Florida appears to greatly increase the
probability of escape from velvetbean caterpillar problems.
Peak numbers of ovipositing adults are probably missed by
planting early. Also the older plants may be less attractive
as oviposition sites than younger plants.
There were differences in the average numbers of VBC,
FAW, and CEW larvae sampled from various age classes of
peanuts 1976-1978 (Fig. 6); Field L was not included
because of its atypical planting date. Larvae of VBC were
most numerous in peanuts 15-17 weeks old. Larvae o^ FAW
fluctuated in abundance, but in general were abundant in
peanuts 12-18 weeks old. Larvae of CEW were most abundant
in 12 week old peanuts, which is ca. 1-2 weeks after peak
28
flowering. These data indicate that VBC and FAW larval
abundance is probably more related to sample date rather
than plant age. Corn earworm larval abundance appears to
be more equally related to both sample date and plant age,
perhaps because CEW prefers to oviposit in flowering fields.
Plusiinae loopers were most numerous from mid-July
through August (Fig. 7). Highest densities of loopers were
reached in Field D where 2.3 loopers per sample were present
on 18 July. Loopers were the most numerous larvae in Field E.
Granulate cutworm (GCW) larvae demonstrated no clear
seasonal trend between years (Fig. 8). In 1977 and 1978
GCW larvae were most abundant in June while in 1976 GCW
larvae were most numerous from late July to early August.
The lack of clear seasonal fluctuation may be due to the
sampling method. Granulate cutworm commonly spend daylight
hours buried in the soil and thus are best sampled between
12:00 AM and 5:00 AM (Eden et al. 1964).
Numbers of beet armyworms (BAW) peaked at different
times of the season for the 3 years the survey was conducted
(Fig. 9). In 1976 BAW larvae were most numerous during
late July while in 1977 and 1978 larvae were most numerous
in mid-June and early July, respectively. Beet armyworms
were never more numerous than 0.7 per sample during this
study
.
There were no distinct generations of foliage feeding
larvae on north central Florida peanuts detected in this study.
Previously 2-3 generations of velvetbean on soybeans were
29
detected by Menke and Greene (1976) and Strayer (1973).
For most species, except for VBC , larvae gradually increased
over G-7 weeks, peaked, and then gradually declined over 2-3
weeks. Larvae of VBC in early planted peanuts remained at
low numbers throughout the season. In late planted fields
VBC larvae were present for 5 weeks or more before a sharp
increase in numbers occurred. Decline of VBC except for
insecticide intervention on late planted fields was very
slight
.
The larval development periods of FAW, CEW , and VBC
on peanuts are relatively long compared to that of other
plant hosts (Huffman and Smith 1979, Nickle 1977). The
duration of the larval stage is generally 20-30 days on
peanuts compared to 12-25 days on other hosts. Parasitism
of larvae of fall armyworm and corn earworm is 20-60%
(Nickle 1977). Predation further reduces survivors. It is
possible that peanuts act as a trap crop or a sink for
these pests--i.e. few eggs laid by moths survive to the
adult stage.
30
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31
Table 2. Relative abundance of lepidopterous larvaeassociated with Alachua County^ Florida^'Florunner' peanuts, 1976-1978.
„ . % of total larvae sampledSpecies
1976 1977 1978
Anticarsia gemmatalis 38., 7 24 .,4 52. 2
Feltia subterranea 6., 1 4 ., 0 3.0
Ileliothis spp. 14., 8 42,,6 20. 5
Plusiinae loopers 10,. 7 0,.6 7.3
Spodoptera frugiperda 25,, 7 22,,4 13.3
Spodoptera exigua 1..6 5,,0 0.4
Other Spodoptera spp. 1,, 5 0,, 7 1.7
Other 0,. 9 0., 3 1.7
"'"Total number larvae sampled 1976, 1977, and 1978 were 15,6613,403, and 1,982, respectively.
Figure 1. Location of Alachua County, Florida, peanut fieldssampled in survey of peanut arthropods, 1976-1978.
Figure 2. Mean numbers of FAW, CEW, and VBC larvae sampledfrom Alachua County Florida peanuts 1976-1978.Breaks in lines indicate dates of insecticideapplicat ion
.
12
10
8
6
4
2
0
I 2
10
8
6
4
2
0
9 6
8 8
8 0
7 2
6 4
5 6
4 8
4 0
1 2
2 4
16
0 8
0 0
8 8
8 0
7 2-
6 4
5 6
4 8
4 0
3 2
2 4
I 6
0 8
0.0
35
Field A1976
FAW—CEWVBC
Field B1976
FAWCEWVBC
Field C1976
-FAW-CFW•VBC
I\
/ \
/ \
\
Field D1976
FAWCFWVBC
/1
1
JUNE JULY AUG SEPT
gure 2. Continued.
37
I 425
I 250
I 000
0 750
0 500
0250
0000
IxJ
_JQ.
<CO
01LUQ_
crLUCD
<1x1
8 8
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6456
4 8
40
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33
30
27
24
2 I
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192
176
160
14-1
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I I 2
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00
Field E
PAW-CF.W•VI3C
Field F19/6
FAWCEW-VBC
Field G1976
F-AW
-CFW•VBC
F leld H1976
------FAW' - a wmc
JIINL St PT
Figure 2, Continued.
39
LlI
_JCL
<
crLUQ.
(TLUCD
<LU
2 6
4
2 2
2 0
I 0
I 6
I 'J
I 2
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FIELD I
1976— FAWCEWVBC
FIELD J
1976
FAWCEWVBC
FIELD K1977
FAWCEWVBC
FIELD L1977
--FAWCEWVBC
JUNt JULY AUG StF'T
gure 2. Continued.
41
Figure 3. Mean numbers of FAW larvae sampled from AlachuaCounty, Florida, 'Florunner' peanuts, 1976-1978.
43
Figure 4, Mean numbers of CEW larvae sampled from AlachuaCounty, Florida, ' Florunner ' peanuts, 1976-1978.
45
Figure 5. Mean numbers of VBC larvae sampled from AlachuaCounty^ Florida^ 'Florunner' peanuts, 1976-1978.
47
O
CD
d
W
O•H
d>
O I>^ aiH
-ci
1
COI>
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E
CO
CD
>cu
rH
CD
u G
uorH
fin d
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om 0> rH
o >^pU
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d
Od dcu rHs
CD
CD
•H
Ph
49
^ ro CJ "~ OMOd dO lAJ 16' d3d 3VAdVn
ddaiAiriN NV31M
Figure 7. Mean numbers of Plusiinae looper larvae sampled
from Alachua County, Florida, 'Florunner' peanuts,
1976-1978.
51
Figure 8. Mean numbers of GCW larvae sampled from AlachuaCounty , Florida, 'Florunner' peanuts, 1976-1978.
53
Figure 9. Mean numbers of BAW larvae sampled from AlachuaCounty, Florida, 'Florunner' peanuts, 1976-1978.
55
SEASONAL DYNAMICS OF PREDACEOUS ARTHROPODSIN NORTH CENTRAL FLORIDA PEANUTS 1976-1978
Introduction
Peanuts in Florida are damaged by numerous injurious
insects and mites. The most injurious pests in Florida are
lesser cornstalk borer, Elasmopalpus lignosellus (Zeller),
spider mites, and foliage feeding noctuid larvae. With the
exception of data on Labidura riparia (Pallas) collected
in pitfall traps in Florida peanuts (Travis 1977) there
have been no studies of seasonal incidence of predators.
The importance of predators in inducing mortality of pest
species has been recognized in other row crops with similar
noctuid larval pests such as cotton (Whitcomb and Bell 1964,
van den Bosch and Hagen 1966), and soybeans (Buschman et al
.
1977)
.
There are few reports of incidence of predaceous arthro-
pods in peanuts. Martin (1976) found Coleomegilla maculata
(De Geer) and Geocoris punctipes (Say) to be the most numer-
ous predators, with spiders, and 2 reduviids Zelus cervicalis
Stal, and Sinea spinipes (Herrich-Schaf f er ) present in low
densities in small peanut plots in north Florida. Predaceous
insects most commonly found in Texas peanut fields are lady
bugs, assassin bugs, lace-wings, ground beetles, predaceous
56
57
stink bugs, big-eyed bugs, Nabis , Orius , and praying mantids
(Smith and Hoelscher 1975). The objectives of this research
were to describe the seasonal incidence, species composition,
and relative abundance of predaceous arthropods on peanuts
and make preliminary tests of associations between the most
numerous predator groupings and major noctuid larval pests.
Materials and Methods
A total of 14 Alachua County, Florida, growers ' fields
of 'Florunner' peanuts were surveyed during 1976-1978 for
relative density of predaceous arthropods. The fields are
described in Table 1. Samples were taken at weekly inter-
vals starting on 6 July, 15 June, and 23 June in 1976, 1977,
and 1978 respectively, and continued until harvest. A total
of forty 0.91 m of row samples were taken at each sample
date by the ground cloth method.
Samples were taken by folding back the branches and
gently placing a ground cloth 0.91 X 0.91 m against plant
bases of one side of the row. The peanut canopy was beaten
downward vigorously with forearm and hands 6 to 8 times
over the cloth to dislodge arthropods. Arthropods that
were observed under the branches while inserting the ground
cloth or on the ground cloth were identified, counted, and
recorded
.
In 1976-1977 samples were taken throughout the field in
a manner similar to that used by commercial scouts. All
areas of the field were sampled in a random manner with not
58
more than 10% of the samples within ca. 20 m of field edge.
In 1978 samples were taken along the transects of an X-shaped
pattern which was aligned along the diagonals of the field.
Twenty samples per transect were taken every tenth row in
Field M and every thirteenth row in Field N. Each week
sampling began on a different row.
A test of association between the most abundant predator
groupings and lepidopterous larvae was calculated using
Kendall's tau-b as suggested by Fager (1957). The Kendall's
tau-b statistic is a nonparametric index of order association
which conforms to Kendall's criteria for correlation coeffi-
cient (Kendall and Stuart 1961).
Results and Discussion
Due to the difficulty of identifying many of the
predaceous species present, certain predators were grouped
either in the field or in this report. The composition
of the predaceous insect fauna varied considerably with
field and year (Table 3). The most numerous predators
sampled were ants, spiders, Geocoris spp., L. riparia,
nabids, and ground beetles (Table 3). This predator complex
comprised 91-99% of the predators sampled.
Ants were often the most numerous predator observed
composing from 13-50% of the total number sampled. In
unsprayed fields ants were generally present in over 75%
of the samples. The most commonly observed ant species
were Solenopsis geminata (Fabricius), Pheidole spp., and
Conomyrma insana (Buckley). Whitcomb et al. (1972)
59
recorded over 60 species of ants from Florida soybeans.
Since the crops are grown in the same area and are host
to similar pests, the ant fauna of peanuts is probably as
complex. Ants were numerous from June through September
(Fig. 10).
Considered as a group, spiders composed 9.9-45%
of the predators sampled (Table 3). In most fields spi-
ders did not exceed 20% of total predators sampled except
for Fields K, M, and N. In 1978 spiders were classified
into 8 categories as follows: 30.4% other spiders; 19%
small spider species and immatures; 15.87o wolf spiders
(Lycosidae); 12.87o jumping spiders (Salticidae) ,7.0%
crab spiders ( Thomisidae ) ; 5.7% striped lynx, Oxyopes
salticus Kent (Oxyopidae) , 5.5% Chiracanthium inclusum
(Hentz) and Aysha gracilis Hentz (Clubionidae and Anyphae-
nidae, respectively); and 3.8% green lynx Peucetia viridans
(Hentz) (Oxyopidae). Spiders were common predators for
the entire season and increased in number slowly during
the season (Fig. 10).
Big-eyed bugs, Geocor is spp., comprised 2.1-16% of the
prfdator complex. In 1977. 17.9% of the Geocoris counted
were G. ulignosus (Say) adults, 5.7% G. ul i gnosus nymphs,
38.6% other Geocoris spp. adults, and 37.8% other Geocoris
spp. nymphs (n=352). In 1978, G. ulignosus adults comprised
24.9% of the total, G. ulignosus nymphs 12.2%, G. punctipes
(Say) adults 19.27o, and 43.7% other Geocoris spp. nymphs,
and no G. bullatus (Say) adults were sampled (n=213).
60
From relatively low numbers at the start of the season,
Geocoris numbers increased gradually, reached a peak of
0.43 per sample, then declined in number during September
(Fig. 11).
The striped earwig, L. riparia ,fluctuated widely in
abundance between fields composing 1.8-47.4% of beneficials
sampled. Most of the L. riparia sampled were observed
while parting the foliage in preparation for beat cloth
placement. Labidura riparia numbers climbed rapidly
from very low initial numbers to greatest numbers of 1.1
per sample at the season's end (Fig. 10). Mark-recapture
analysis of absolute earwig population levels in 2 Alachua
County peanut fields during late August and early September
indicated maximum populations of 34,400-85,227 earwigs/ha
(Travis 1977).
Nabids were relatively abundant only midway through the
season and a decline in nabid numbers occurred in September
(Fig. 11). In 1976 Tropicanibis capsiformis (Germar) and
Reduviol is roseipenn is (Reuter) composed 99 and 1%, respec-
tively, of the total nabids collected for identification
(n=100). Of 240 nabids sampled in 1978, 96% were T. capsi -
formis , 2.5% were R. roseipenn is , and 1.5% were Pagusa
fusca (Stein )
.
Adults of the insidious flower bug, Or ius insidiosus
(Say), reached peak abundance during mid-June and July, then
declined sharply (Fig. 11). Patterns of abundance of 0.
insidiosus may be associated with peanut flowering since
61
pollen seems to be an important part of diet of both nymphs
and adults (Dicke and Jarvis 1962). Also, tobacco thrips
are most abundant before flowering and may serve as prey.
Ground beetle adults and larvae composed 3.2-9.5% of
the predator complex. The most numerous species of ground
beetle were the foliage dwelling Cal 1 ieda decora (Fabricius).
Cal lieda decora comprised 75 and 53% of the carabids sampled
in 1977-1978 respectively, Peak abundance of C. decora
larvae occurred near peak numbers of fall armyworm and corn
earworm. Collurius pennsylvanicus (Linnaeus) adults composed
7.3 and 47% of the carabids collected in 1977 and 1978,
respectively. Other carabids infrequently encountered were
adults of Anisodacty lus merula Germstacker, Selenophorus
palliatus Fabricius, S. ellipticus Dejean and Teragonoderus
intersectus Germar and larvae of Progalerit ina spp. and
Calosoma say
i
Dejean.
Many of other predaceous arthropods occurred in numbers
too low for assessment of their seasonal dynamics. None
of these predators averaged more than 0.5 per sample on a
given date during this 3 year study. Some of the predators
that were observed in most fields in low numbers include:
Doru taen latum (Dohr) ( For f icul idae ) ,Spanogon icus albof as -
ciatus (Reuter) (Miridae) , Zolus cervical is (Stal) (Reduvi-
idae), Sinea spp. (Reduviide), Podisus macul 1 ventrus (Say)
(Pentatomidae ) ,Chrysopa spp. larvae ( Chrysopidae )
,
Scymnus spp. adults ( Coccinel 1 idae ) and Noxtoxus spp. adults
( Anthicidae)
.
62
Classical predator-prey theories predict gross predator
population density fluctuations similar to the host-popula-
tion's gross variations (Watt 1968). Significant positive
correlations demonstrate associations or similar patterns
of variation between larvae and predaceous arthropods.
The explanation for association may be chance, or indicative
of density dependence phenomena.
Spiders were significantly correlated with foliage
feeding larvae (FFL) twice, velvetbean caterpillar (VBC)
6 times, and fall armyworm (FAW) once (Table 4). For
earwigs there were 6 significant associations involving
FFL once and VBC 5 times. Nabids had the greatest total
number of correlations. Nabids were correlated with FFL
4 times, VBC 11 times, and FAW once. Geocoris spp. showed
few correlations; they were associated with VBC twice, FAW
twice, and CEW twice. Ants were associated with VBC once,
the fewest significant associations of all predator group-
ings. Orius insidiosus adults showed significant correla-
tions with FFL twice, FAW 3 times, and CEW 3 times.
For further elucidation of association patterns a
refinement in sampling technique and statistical analysis
is needed. Absolute samples or calibrated relative samples
of pests and beneficials analyzed using multivariate analysis
may prove useful in clarifying associations.
Some inferences about the relative importance of pre-
daceous arthropods on north Florida peanuts can be made.
63
Ants were the most numerous predators sampled and
probably one of the most important predators regulating
pest populations. Ants have been frequently observed con-
suming lepidopterous eggs in Florida soybeans (Buschman et
al . 1977, Nickerson et al . 1977). Lack of many significant
correlations between larvae and ants is not surprising
considering ants were one of the most under-sampled predators
in this study. Some species of ants only forage at night
(Whitcomb et al . 1972) and most ants are underground at any
given time.
Because of the abundance of families represented spiders
occupy a variety of feeding niches. Whitcomb (1974) stated
4 important roles of spiders as follows: (1) spiders prey
on destructive insects; (2) spiders serve as food for pred-
ators; (3) spiders tend to be general feeders, and (4) spi-
ders compete with insect predators for prey. Spiders have
been reported as important egg predators in Florida soybeans
(Buschman et al . 1977). The abundance of spiders in peanuts
suggests they are important in effecting pest population
dynamics
.
Eggs and small larvae of noctuids are part of prey of
Geocoris spp. However Geocoris spp. consume a very broad
array of prey (Crocker 1977). Menke and Greene (1976)
reported large Geocoris spp. populations exerted little
population regulation of velvetbean caterpillar populations
in north Florida soybeans. Consequently, Geocoris spp. were
probably not major predators in north central Florida peanuts.
64
The habits of ground beetles are extremely varied
often within the same genus. Callieda decora was the only
ground beetle sampled in sufficient numbers to be important
in some fields. In 1977 C. decora was observed numerous
times feeding on small to medium corn earworms. Calosoma
sayi adults and larvae were numerous in pitfall traps in
peanut fields with high VBC populations in 1976 (Travis
unpubl.). Calosoma sayi consumes and reacts to noctuid
pests of soybeans by taking progressively more prey items
as they become available (Price and Shepard 1978). Calosoma
sayi is one of the few potentially important predators
of large larvae and pupae in peanuts.
Labidura riparia were important predators in most
fields during this study. Earwigs were especially uncommon
in Field N in 1977; it is possible that application of para-
thion on 6 July followed by a 27 July application of
monocrotophos may have greatly reduced the earwig popula-
tion in this field. All stages of noctuids may be consumed
by L. riparia (Schlinger et al. 1959, Hasse 1971, Neal 1974).
In laboratory tests functional response of earwigs to noctuid
larvae prey indicated that successful attacks increased
with higher host density (Price and Shepard 1978). That
L. riparia. numbers were associated with foliage feeding
larvae was demonstrated by significant correlation coefficients
and the gradual increase in earwig numbers during the season
(Fig. 10). L. riparia is considered an important predator
65
in Florida soybeans (Neal 1974, Buschman et al . 1977).
Labidura riparia is probably one of the most important
predators in peanuts in north central Florida.
T. capsiformis adults and nymphs were potentially
important predators of VBC larvae. The increase in nabid
populations closely followed the increase in VBC larvae.
Nabids were uncommon earlier in the 3 seasons when FAW
and CEW were present. Nabids consume eggs and small larvae
of noctuid pests.
0. insidiosus was not numerous during the season when
defoliators were numerous. However, 0. insidiosus may
have served to suppress early season outbreaks of some
pests during June. During the increase in VBC numbers 0.
insidiosus were not common.
66
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71
SPATIAL DISTRIBUTIONS OF DEFOLIATINGLEPIDOPTEROUS LARVAE ON PEANUTS
Introduction
Spatial distributions are a useful means of quanti-
fying the dispersion of insects in a given habitat. Spatial
distributions are useful in several ways: (1) to aid in
determining the appropriate transformation for analysis of
variance; (2) to develop sequential decision plans; and
(3) to develop sampling plans. Also, inferences about the
biology of the insect e.g., dispersal patterns, can be
made. Spatial distribution models are probability distri-
butions that relate the frequency of occurrence of an event,
depending on the mean of the measurements and in some cases
on one or more parameters.
The most useful statistical distributions in entomo-
logical research have been the Poisson and negative binomial
(Southwood 1978). The Poisson distribution describes a
random distribution with variance equal to the mean. Most
commonly in insect sampling the variance will be larger
than the mean, indicating that the distribution is aggregated
or clumped. The most useful distribution describing a
clumped insect population has been the negative bionomial.
72
73
The versatility of this distribution arises from the fact
that it may be derived from at least 5 different models
(Waters and Henson 1959).
The objective of this study was to determine the spa-
tial distribution of the major foliage feeding insect pests
of peanuts in Florida.
Methods and Materials
Forty samples per week were taken by the ground-cloth
shake method from 0.91 m of row from growers' fields of
'Florunner' peanuts, 1976-1978. Thus the field counts of
foliage feeders were taken from different field sizes and
population densities.
Insects sampled included velvetbean caterpillars,
Anticarsia gemmatalis Hubner; fall armyworm Spodoptera
f rugiperda (J. E. Smith); corn earworm, Ileliothis zea
(Boddie); granulate cutworm Feltia subterranea (Fabricius);
•and Plusiinae loopers : Trichoplusia ni (Hubner), Pseudo -
plusia includens (Walker), and Argyrogramma verruca,
(Fabricius). Mixed populations of loopers prohibited
differentiation of these species in the field.
Data sets were arranged into discrete frequency classes
and fitted to mathematical distributions utilizing a compu-
ter program developed by Gates and Ethridge (1972). Only
those data sets with 4 or more frequency classes were
analyzed and fitted to a distribution. The observed
74
frequency distribution for the following distributions:
Poisson, Poisson-binomial , Poisson with zeroes, negative
binomial, Neyman type A, and Thomas double Poisson.
The iterative solution technique of Bliss and Fisher
(1953) was used determining the parameter k of the negative
binomial. Common k values were calculated by the iterative
method (Formula 10) of Bliss and Owen (1958).
Results and Discussion
Data sets of counts of lepidopterous larvae fitted
the negative binomial or Poisson with zeroes better than
any other distribution (Table 5). Data sets obtained from
counts of fall armyworm and velvetbean caterpillar fit
the negative binomial significantly better than Poisson.
The percent fit of data sets to the negative binomial for
all larvae was relatively high— i.e. 82-90% while similar
studies in soybeans by Shepard and Garner (1976) and in
cotton (Kuehl and Fye 1972) showed lower fits of negative
binomial for some of these same species. The Poisson
distributions fit the data fewer instances, 41-70% in every
case
.
Values of common k for larvae were 3.93 for fall army-
worm, 5.20 for corn earworm, 7.27 for velvetbean caterpillar,
2.51 for granulate cutworm, and 3.58 for loopers. Only the
oformer 2 common k values significantly fit (P=0.05) a
test for homogeneity of k in the different samples.
75
The value of k may not be a constant for a population
but often increases with the mean. However, regressions
of 1/k versus population means for individual species were
not significant P=0.05. This indicates that k values and
means were not related. Large variation in sample k values
caused the lack of fit. Neither size or age classes of
larvae were considered in fitting distributions. Grouping
instars may have increased the k values by combining the
different instar distributions.
When action economic thresholds for peanuts are revised
sequential sampling plans may be developed using the formula
presented by Waters (1955). The common k values determined
for fall armyworm and corn earworm can be used for calculat-
ing decision lines. The formula for decision lines for
populations described by the Poisson distribution will be
adequate for the other species of lepidopterous larvae.
76
Table 5. Percentage fit of counts of foliage consuming lepidop-terous larvae to the expected frequency distributions,1976-1978.
Fall Corn^ 3,VelvetbeanRank armyworm % Fit earworm % Fit caterpillar
1 Neg. binomial 84 Poisson /zeroes 84b Neg. binomial
2 Neyman 73b Neg. binomial 82 Neyman
3 Poisson-bin
.
69b Neyman 82b Poisson-bin
.
4 Thomas 66b Poisson-bin
.
77b Poisson/zeros
5 Poisson/zeros 65b Thomas 73b Thomas
6 Poisson 41d Poisson 61b Poisson
Number of observed frequency distributions equals 51 for FAW,44 for Ileliothis spp., 39 for VBC , 33 Cor loopers , and 28 forGCW
% fit not significantly different from the % fit of the nega-tive binomial distribution at the 57o level
% fit significantly different from % fit of negative binomialat 5% level
% fit significantly different from % fit of negative binomialat 1% level
77
Table 5. — Extended
Granulate% Fit Loopers^ % Fit cutworm % Fit
87 Poisson/zeros 94b Neg. binomial 90
80b Neg. binomial 88 Neyman 85b
77b Neyman 82b Thomas 85b
74b Thomas 79b Poisson/zeros 82b
61b Poisson-bin. 73b Poisson-bin. 75b
54c Poisson 70b Poisson 68b
EFFECTS OF UNIFORM HAND DEFOLIATION OFPEANUTS ON PLANT GROWTH
Introduction
Peanut (Arachis hypogaea L.) yields in the southeastern
United States may be reduced by a complex of arthropod
pests. Most of the insecticide applications in the south-
eastern peanut belt are made to control foliage feeding
noctuid larvae (French 1973). Foliage feeding larvae report-
ed capable of causing yield loss include corn earworm,
Heliothis zea (Boddie), fall armyworm, Spodoptera f rugiperda
(J. E. Smith), and velvetbean caterpillar, Anticarsia
gemmatal is (Hubner) (Bass and Arant 1973). In Florida,
noctuid larvae may become numerous 10 weeks after planting
and damaging levels of larvae may occur until harvest.
Information relating peanut foliage loss to yield
is variable for a given plant age and variety. Previous
defoliation experiments have dealt with peanut varieties
other than 'Florunner' (Enyi 1975, Williams et al. 1976,
King et al. 1961) or have examined only the influence of
defoliation of 'Florunner' on yields only (Greene and Gorbet
1973, Nickle 1977).
A mowing machine was used by Greene and Gorbet (1973)
to remove the upper portions of peanut canopies to approx-
imate 5 levels of defoliation of 'Florunner' peanuts in
7S
79
Florida. Removal of an estimated 33% of leaf area reduced
yields 5-44% except for a 2% yield increase at 81-90 days
after planting. Yield reductions averaged for the 3 years
of defoliation experiments at 58, 65, and 108 days after
planting were 3.8, 13, 21.5, and 44% yield loss from 10-15,
20, 33, and 50% defoliation, respectively. At the 507o
defoliation level some stems and pegging branches also
were removed.
Nickle (1977) hand defoliated unirrigated 'Florunner'
peanuts in Florida at 5 dates. Yield reductions averaged
2-6.8, 7.2-21.6, 16.8-41.2, and 20-51% from 25, 50, 75,
and 100%. defoliation respectively for the 2 defoliation
experiments. Greatest yield reductions for both experiments
resulted when defoliation occurred at 63 days after seed-
ling emergence.
Few studies describe how defoliation affects peanut
canopy characteristics and plant growth. Boote et al . (1980)
reported the effect of 75% hand defoliation of the upper
42% of canopy leaf area of unirrigated 'Early Bunch' peanuts.
Measurements were made of light interception, specific
leaf weights (SLW) , leaf area index (LAI), apparent canopy
14carbon exchange, and photosynthet ic uptake of CO^
4 days after defoliation. Effects of defoliation on peanut
growth and yield are being quantified using a modeling
approach (G. Wilkerson"*") . Simulation of peanut defoliation
'"Ms. Gail Wilkerson, graduate assistant, Univ. of Florida.
80
will enable the experimental control of the many interacting
factors (environment, insect populations, crop phenology)
at will. Current peanut plant growth models (Duncan 1974,
Young et al . 1979) lack components for coupling defoliation
to plant growth. Objectives of the present study were to
describe how defoliation affects canopy characteristics
and plant growth.
Materials and Methods
Peanuts cv. 'Florunner' were hand planted in 3 blocks
42m X 22 rows 22-23 May 1978 at the University of Florida
Agronomy Farm, Alachua County, Florida. The soil type was
Arrendondo fine sand. Row spacing was 76.2 cm with plants
spaced 13.8 cm apart in the row, which is within the range
of plant population for maximum yield (Malagamba 1976).
Weed control was achieved with preplant ( . 6 kg a.i./ha
benfluralin and 2.3 kg a.i./ha vernolate) and cracking time
(2.8 kg a.i./ha dinoseb and 2.4 kg a.i./ha 2,4-DEP) herbi-
cides. Ethylene dibromide (253 ml/chisel/lOOm) was injected
5 days before planting for nematode control. Gypsum was
applied by hand at 1700 kg/ha on 26 June. The fungicide
chlorothalonil was applied at 0.8-1.1 kg a.i./ha starting
on 22 June at 7-10 day intervals until 22 September.
Monocrotophos (1.9 kg a.i./ha) was applied on 29 June
for lesser cornstalk borer ( Elasmopalpus lignosellus (Zeller)).
Either methomyl ( . 6 kg a.i./ha), carbaryl (1.2 kg a.i./ha) or
81
acephate (1.1 kg a.i./ha) were used to kill foliage feeding
noctuid larvae (corn earworm, velvetbean caterpillar,
fall armyworm, and Plusiinae loopers) and were applied at
7-14 day intervals from 15 July until 22 September. Insec-
ticides and chlorothalonil were tank mixed and applied with
a pressurized backpack sprayer. On 24 August f ensulfothion-
PCNB granules (40.3 kg a.i./ha and 13.4 kg a.i./ha, respec-
tively) were broadcast by hand to slow the spread of white
mold, Sclerot ium rolfsii Sacc. infestation. Overhead
irrigation was used to prevent extreme water stress. Pes-
ticides and cultural practices used were designed to minimize
pest damage and still be reasonably similar to typical
grower practices.
Four levels of defoliation were obtained by removing
0, 1, 2, or 3 leaflets from all tetraf foliates with a peti-
ole extension, corresponding to 0, 25, 50, and 75% defolia-
tion, respectively. Fifty leaflets from 3 plots of each
defoliation treatment were saved for leaf area determination
with an automatic area meter and drying at 70° C.
Defoliation and check plots were selected for uniformity
at 5 weeks after planting and assigned randomly to treatments.
Defoliation plots were 1.1 m lengths of row with (1) at
least 1.5m between plots in the same row and (2) undefolia-
ted adjacent border rows. Plots were defoliated at 25, 50,
and 75% at 8, 11, 13, and 15 weeks after planting. At 17
weeks the only defoliation level was 75%. In addition.
82
there was (1) a treatment at 8 weeks of 75% defoliation plus
removal of buds for 7 days and (2) a redef oliation treatment
of 75% defoliation at 15 weeks of some plots 75% defoliated
at 11 weeks.
At 2 week intervals, starting 2 weeks after a defolia-
tion, until harvest at 19 weeks after planting, 3 samples
of 75% defoliated plots of 11, 13, 15, and 17 weeks were
removed. At 19 weeks after planting 4 plots of all treat-
ments were harvested for yield. Similarly, undefoliated
plots were removed at 8, 10, 11, 13, 15. 17, and 19 weeks.
Four replicate samples of the 8th week defoliations also
were removed at 10 weeks. One plant from each plot, not
one of the plants bordering undefoliated plants in the row,
was separated into roots, stems, leaves, pod shells, and
kernels for dry weight determination. The remaining plants
in the plots were dried and total plot weights were obtained
by summing plant parts of a plot and remaining plants.
Leaflets from undefoliated plots were separated into leaflets
present at defoliation ("old" leaves) and intact leaves
("new" leaves) expanded since defoliation date. Leaf area
and dry weights were measured from 50 "new" and "old"
leaves. Single plant part percentages and total plot weight
were used to calculate dry weights of plant parts per unit
area
The photosynthetically active radiation (PAR) inter-
cepted by peanut canopies was measured 1-3 days after defol-
iation using a pyranometer (LI-200S)^ in conjunction with
83
a quantum-radiometer-photorneter (LI-185) , and pringing
integrator (LI-550)"'". Photosynthetically active radiation
measurements were taken 1-3 days after defoliation on days
of clear skies between 900-1500 hours EST. A metal track 3
wide with 3 cm sides was inserted perpendicular to the row
between plants. The pyranometer was pulled by its cord
manually along the track at a timed constant rate for 1
minute. An ambient full sun reading above the canopy was
recorded within 1-2 minutes of canopy reading.
Results and Discussion
The daily rainfall, irrigation, solar radiation,
maximum and minimum temperatures from planting until harvest
are given in Appendix Table 12.
Percent light interception of peanut canopies under
different levels of defoliation at different plant ages
is given in T.ble 6. The LAI for intact canopies was
3.11, 4.52, 5.65, 6.09, 5.53 and 5.45 at 8, 11, 13, 15, 17,
and 19 weeks after planting, respectively. Quadratic
regressions for LAI and percent light interception of
intact canopies and of canopies defoliated 27-75% at 8,
11, 13, 15, and 17 weeks after planting were calculated
(Fig. 12). Two LAI—percent light interception coordi-
nates taken at 6.5 and 9 weeks after planting used in the
''"Lamba Instruments Corporation, Lincoln, NE
.
84
intact canopy regression were taken from an adjacent peanut
experiment (G. Wilkerson unpubl.)-
Differences in canopy structure at a given LAI is a
probable explanation for the difference in regression equa-
tions of light interception—LAI for intact defoliated
canopies. In general, most of the LAI data used to fit the
defoliated canopy curve represent canopies with greater stem
areas and ground cover. Ten of the 13 defoliated canopies
had an LAI less than 3. Of these 10 canopies, 7 were from
plots 11 or more weeks old. Stem growth is almost complete
at 11 weeks and stems intercept 39% of ambient light when
2leaves are removed from full grown plants (Jones et al.
unpubl.). By 11 weeks ground cover was 100%. The stem
light interception plus the possibly more uniform spacing
of leaves on plants exhibiting 100% ground cover compared to
intact canopies with a LAI less than 3 probably caused the
higher light interception readings of defoliated canopies
at a given LAI
.
To estimate the difference in crop and pod growth
rates of intact and 75% defoliated canopies at 11 and 13
weeks after planting, linear regression curves of dry
weights versus plant age were calculated. Since more photo-
synthate is necessary for kernel development than other
plant parts, a result of the higher concentration of oil
and protein in seeds than in other plant parts, an adjust-
J. W. Jones, C. S. Barfield, K. J. Boote, G. H. Smerage,and J. Mangold. Photosynthetic recovery of peanuts todefoliation at various growth stages. MS in review.
85
ment was used. Average values of the correction factors
developed by Hanson et al. (1961) and Penning de Vries
(1974) for seeds--i.e. 1.88 X kernel weight were used.
The growth response of intact plants, 75% defoliation
at 11 weeks, and 75% defoliation of plants at 13 weeks is
illustrated in Fig. 13. Regression equations for crop
and pod growth rates are presented in Table 7. The crop
growth rate of intact canopies appeared to slow late in
season. The decrease in growth rate was probably due to
the few new leaves that are added and the photosynthetic
rate of older peanut leaves decreases with age ( Trachtenberg
and McCloud 1976, Henning et al. 1979).
There was a greater relative reduction in pod and crop
growth rate of plants defoliated at 13 weeks than at 11
weeks. For plants defoliated 75% at 11 weeks, crop and pod
growth rates were 71.7 and 76.1%, respectively, that of the
undefoliated . Seventy-five percent defoliation at 13 weeks
reduced crop and pod growth rates by 65.3 and 57.1% that
of the undefoliated plants. A plausible explanation for the
larger reduction in growth rates of 13th week defoliated
plants versus 11th week defoliated plants may be related to
the lower average LAI present of 13th week defoliated
plants during the remainder of the growing season. Plants
defoliated in week 11 added LAI.
Partitioning coefficients were calculated from the crop
and pod growth rates. Partitioning refers to the division
86
of photosynthate between reproductive and vegetative plant
parts. Previously pod partitioning coefficients of undefol-
iated 'Florunner' peanuts has been estimated at 73% by
linear regression of dry weights (McGraw 1977) and 84.7% by
the PENUTZ model (Duncan et al . 1978). The calculated pod
partitioning factors for the undefoliated plots from 11-19
weeks and 13-19 weeks. 75% defoliation at 11 weeks, and
75% defoliation at 13 weeks were 75.1, 80.9, 70.7, and 92.5%
respectively
.
Specific leaf weights of defoliated plants significantly
increased in some cases after defoliation as compared to
undefoliated plants (Tables 8, 9). Most of the increase
in SLW was attributed to the increase in "old" leaf SLW.
Old leaves increased in SLW probably due to less shading.
Decreases in SLW with shading for peanuts (An 1976) and
other legumes such as alfalfa, Medicago sativa L. (Wolf and
Blaser 1972) and soybean, Glycine max (L. ) Merr., (Cooper
and Quails 1967) have been reported.
An increase in SLW may be related to increased photo-
synthetic rates. Bhagsari and Brown (1976) detected a
significant positive correlation between SLW and photo-
synthesis in 1 of 3 experiments involving peanut genotypes.
However, no correlation between SLW and net photosynthesis
of peanut leaves were found by Pallas and Samish (1974).
Defoliation reduced yields at most levels and plant
ages, but significant differences from undefoliated peanuts
87
occurred only with 75% defoliation at 8 weeks plus removal
of buds for 7 days, 757o defoliation at 11 weeks, and multiple
75% defoliations at 11 and 15 weeks (Table 10). Early pod
fill ca. 68-day-old plants has previously been shown as the
plant age most sensitive to defoliation (Nickle 1977)
.
Consumption or damage to terminal buds appeared to be an
important compounding effect to uniform canopy defoliation.
The early instars of corn earworm feed selectively on leaf
tissues of terminal buds (Morgan 1979). Sustained terminal
bud damage may be an important aspect of defoliator damage
by corn earworm and possibly fall armyworm especially
during the vegetative growth stage of peanuts.
Seventy-five percent defoliation and 75% defoliation
plus removal of buds at 8 weeks reduced pod and stem weights
at 10 weeks (Table 11). Decreases in stem weight of
'Dodoma' edible peanuts with defoliation have been reported
previously (Enyi 1975). The weight of leaves grown 2 weeks
after 50 and 75% defoliation also was significantly higher
than undefoliated plants. Defoliated peanut plants compen-
sated for defoliation by growing more leaves and reducing
stem and pod growth.
Plants defoliated 75%. at 11 weeks grew significantly
more leaves than undefoliated plants during the 2 week period
following defoliation (Table 11). No detectable differences
in leaf growth between defoliated and undefoliated plants
were detected in other treatments or time periods after
defoliation
.
88
Table 6. Average percent light interception of intact anddefoliated 'Florunner' peanut canopies afterdef ol iat ion
Percent Percent light interceptiondefoliation Defoliation date (weeks after planting)
8 11 13 15 17 19
Intact 69. 5 90,,6 96.,9 94 . 0 92,,9 95. 5
25 68. 3 83,, 1 91., 2 81. 8
50 57. 5 80., 0 75. 8 77. 2
75 51. 8 63..4 70. 5 50. 7 60.,6
75+buds 45.2
Buds removed for 7 days.
89
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90
Table 8. Specific leaf weight (SLW) of peanut leaves fromintact and defoliated 'Florunner' peanut canopiesin relation to weeks after planting.
Age at 75% SLW (mg/cm)defoliation Leaf weeks after planting
(weeks
)
type 11 13 15 17 19
1^ o n "t" T*o T 3 83 3.83 3 . 86 4 . 03 4.12
11 new 3 . 85 4.19 4 . 62 4 . bo
old 4.12 4.20 4.63 4.76
avg. 4.02 4.26 4 .63 4.72
13 new 3.09 4.78 4. 51
old 4 . 20 5. 00 4.91
avg. 4. 06 4.96 4.80
15 new 4.01 4.12
old 4.15 4 . 90
avg. 4. 10 4.80
17 new 4.39
old 4.51
avg. 4 .49
LSD for new leaves, old leaves, and svg. leaves=0.39, 0.45, and0.47, respectively, P=0.05.
91
in
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rH O CD P> in o in in rH CJ^-\ rH c CSl in i> d
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92
Table 10. Effect of defoliation of 'Florunner' peanutplants on plant parts at 19 weeks.
Level YieldAge defoliation reduction Pod dry^weight
defoliated % % (g/m )
control 0 • 0 495,. lab
8 25 4 . 02 475 . Oabc
8 50 15. 06 420 . 5abcd
8 75 13. 24 429 . 5abcd
8 75+buds 26. 19 365 .4cd
11 25 6. 48 463 . Oabcd
11 50 18. 54 403 . 3abcd
11 75 29. 50 349 . Od
11 , 15 75 26. 05 366 . led
13 25 30 493 . 5ab
13 50 - 1 . 60 503 . Oa
13 75 23. 64 378 . Ibcd
15 25 6. 00 465 . 3abcd
15 50 10. 30 444 . labcd
15 75 21
.
90 386 . 6abcd
17 75 20. 20 394 . Sabcd
Values in a column followed by same letter are not signif-icantly different (?< 0.05), Duncan's new multiple rangetest
.
93
Table 11. Dry weight of leaves from Intact and defoliated'Florunner' peanut plants 2 weeks after defoliation.
Week of Def oil ationN f^\Ml"i W J. d V o o
1 2Dry weight (g/m )defoliation treatment Week added
11 75% 11-13 40.38a
control 11-13 20.66b
13 75% 13-15 12.06a
control 13-15 16.88a
15 75% 15-17 9 . 03a
control 15-17 -10.60a
17 75% 17-19 4.29a
control 17-19 2.06a
Values in a column, for a given week of defoliation followedby same letter are not significantly different (P<0.05),Duncan's new multiple range test.
+->
d
O *
CD 73
O -
rHl-H 0)
<; >0)
rHOP r-l
OC •
O O•H II
+->
D-••
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95
N0lld33d31NI IHOn lN33d3d
Figure 13. Dry matter accumulation in peanut plant partsin relation to weeks after defoliation. Podweight is adjusted by factor of 1.88 X kernelweight
.
97
1800-
lf>00
MOO
1200
1000UJcr<t 800
O 600-
co400-
crUJ 200-
h-
1400-
crLJ 1200
CL1000-
cr.
LU 800
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600
200
cr
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< 1000
o 800-
600-
400
200-
CONTROL- TOIAlPOOS— LKAVES— STfM---HOOIS
757o-l I WEEKS
757o-l3 WEEKS
10 I I 13
—I
—
15 17 19
APPENDIX
Table 12. Solar radiation, temperature, rainfall andirrigation during growing season, 1978.
Solarradiation Temperature (°C) Rainfall and
Day (Langleys) Max. Min. irrigation (mm)
23 ivicty 4: y o o .o 21 . i
94 O 1 . I 21 . /
/I Q o o oo 20 . 6 5 .
1
oy o 32
.
oO 20.097 bl4 21
.
r-j
f 16 . 19R ODD r-r
1 18.39Q 31
.
7 18.3OU r\ 32
.
2 20 . 0O 1 o n "739 / 32 . 2 19.4 5 . 8i June ooO 32
.
o8 20 . 09 o ri o392 31
.
1 22 . 2oO 292 30 . 0 21.7 25. 9
277 28
.
3 22 . 2 8 . 8O 368 28
.
3 21 . 1
b 485 31
.
1 22. 2I 540 31
.
1 23 . 3 .5Oo rz r\r\o02 33
.
3 24 .
4
9 425 32. 2 23.9 2.510 449 31
.
7 23.9 14.711 449 31. 7 23.3 .312 461 31
.
1 20.613 576 32. 2 23. 314 456 31
.
1 23.3 7.915 464 28. 3 20.016 519 30. 6 18. 917 619 30. 6 18.918 614 30. 6 17. 819 507 30. 6 22. 220 313 29. 4 22. 221 406 32. 2 21.1 10. 222 447 30. 6 22. 2 1.023 578 32. 8 22. 224 478 34. 4 20. 6 26.925 600 32. 2 22. 826 597 33. 9 22. 227 571 33. 3 23.928 497 35. 0 23. 929 554 35. 0 23. 930 600 35. 0 23.9
98
99
Table 12. Continued.
Solarradiation Temperature ( C) Rainfall and
Day (Langleys) Max. Min. irrigation (mm)
1 July 624 33. 9 23. 3
2 636 34.4 23.33 638 33.9 25. 0
4 294 28.3 23.9 3.35 430 31.1 23.9 6.46 258 27.8 21. 1 5.37 335 20.0 22.8 8.48 478 31.1 22. 2 1.29 609 31.
1
22.2 3.810 590 33.3 23.311 449 33.3 23 . 3
12 270 30.6 22.2 9.913 370 27.8 22. 3 .8
14 425 30.0 22.815 480 31.1 23.316 103 31.
1
23.3 37.617 392 30.6 22.8 8.418 485 30.0 23.3 10. 1
19 397 30.6 21 . 7 4.320 411 28.9 22. 2 . 3
21 519 32. 2 22. 2 .8
22 533 32.2 23.3 6.623 624 32. 2 23.324 628 32. 2 22.2 .3
25 583 33.9 22.8 2.026 337 30. 6 21. 7 1.327 454 31. 1 22. 8 77.528 220 27.8 23. 3 7,129 330 29.4 22. 8 9. 1
30 411 31.1 23.9 6.631 249 30.6 21.11 August 432 30.6 21.
1
82. 8
2 502 31 . 7 22. 2 11.93 614 31.7 21.14 514 31. 1 22. 2
5 478 30. 6 22.8 2.36 313 31 . 7 22.27 571 33. 3 21.78 311 30.0 23.9 .3
9 633 31.7 21.7 4.610 387 30.6 22.2 . 8
11 280 30. 0 22. 8 12. 2
12 342 31.7 23. 3 2.813 249 28.9 22.8 1.014 380 30. 0 22. 2
15 485 33.3 22. 8 50. 1
100
Table 12. Continued
Solarradiation Temperature ( C) Rainfall and
Day (Langleys) Max. Min. irrigation (mm)
16 August 387 31.7 22 . 8 . 517 464 32 . 8 21.7 2 . 3
18 576 33 .
9
21.7 2 , 3
19 382 31 . 7 20 . 020 516 33 . 3 23 .
9
21 542 32 . 2 21.122 428 31.7 22 . 223 473 31.1 22 . 224 547 31.7 21.125 456 31.7 20 . 0 12.726 499 32 . 2 21.127 593 33 .
9
22 . 2
28 476 35 . 0 22 . 2
29 571 32 . 2 22 . 2
30 573 32 . 8 22.831 509 32.8 21.7 19 . 1
1 September 466 35 . 0 21.72 413 33 . 3 21.7 1 . 8
3 511 32 . 8 21.74 516 33.3 20 . 05 437 33 .
9
19.46 459 31 . 1 18.37 535 32.2 20 . 08 425 32.8 23 . 3 19 . 1
9 378 32.8 22 . 8
10 217 31.7 20 . 011 487 31 7 18 9
12 499 91 7
13 44Q 39 8 90 n
14 411 9 8 90 fi 1 Q 1
15 416 3 91 1
1 6 41 n o o , o 90 R
1 7 ^9 SO ill . O 9 n n
1 8 T 9 R 9n RZ U . D^ QJL t-/ ^ o o o o . o 1 R 11 O . X
^ o o 10 9i5 <i . ^ 9 n RZU . D 1 Q 1X y . i9 ^ o o u TO 9 9 n ozu . y
Ooo . y 9 A nZU . D^ o OR!Z O X Q 9 9 9 1 1Z J. . 1 1 . b24 385 31.1 21 . 725 435 31 . 7 20. 6 .826 354 30. 0 20.6 12. 727 292 29.4 20.028 378 28. 3 18. 329 170 27. 2 20.630 129 25.6 22. 2 7.91 October 306 28. 9 17.22 456 28. 9 16. 1 12 . 73 485 29.4 19.44 308 29.4 15.6
LITERATURE CITED
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Anonymous. 1977a. Ln Coop. Plant Pest Rep. 2:510.
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Arant, F. S. 1948a. Status of velvetbean caterpillarcontrol in Alabama. J. Econ. Entomol. 41:26-30.
Arant. F. S. 1948b. Control of peanut insects. Ann.
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Arthur, B. W. , L. L. Ilyche. and R. H. Mount. 1959. Controlof the red-necked peanutworm on peanuts. J. Econ.Entomol. 52:468-70.
Barfield, C. S., and J. W. Jones. 1979. Research needs for
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Bhagsari, A. S., and R. H. Brown. 1976. Photosynthesisin peanut ( Arachis ) genotypes. Peanut Sci. 3:1-5.
Bissell , T. L. 1941. A micro leaf worm on peanuts. J.
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Bliss, C. I., and R. A. Fisher. 1953. Fitting the negativebinomial distribution to biological data. Biometrics9: 176-200.
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101
102
Boote, K. J., J. W. Jones, G. 11. Smerage, C. S. Barfield,
and R. D. Berger. 1980. Photosynthesis of peanutcanopies as affected by leafspot and artificialdefoliation. Agron. J. (in press)'.
Bowes, G. , W. L. Ogren , and R. H. Ilageman. 1972. Light
saturation, photosynthet ic rate, RuDP carboxylase:Activity and specific leaf weight in soybeans grown
under different light intensities. Crop. Sci. 11:
77-9.
Boyer, W. P., and W. A. Dumas. 1963. Soybean insect sur-
vey as used in Arkansas. U. S. Dept. Agric. Coop.
Econ. Insect Report. 13:91-2.
v^uschman, L. L.. W. H. Whitcomb, R. C. Hemenway ,D. L.
Mays, Nguyen Ru , N. C. Leppla, and B. J. Smittle.
1977. Predators of volvetbean caterpillar eggs in
Florida soybeans. Env. Entomol. 6:403-7.
Canerday, T. D. , and F. S. Arant . 1966. The looper com-
plex in Alabama ( Lepidoptera , Plusiinae) . J. Econ.
Entomol. 59:742-3.
Cooper, C. S., and M. Quails. 1967. Morphology and chloro-
phyll content of shade and sun leaves of two legumes.
Crop Sci. 7:672-3.
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BIOGRAPHICAL SKETCH
The author was born on October 23, 1951, in Seminole,
Florida. Upon graduation from Seminole High School in 1969,
he entered the University of Florida. In June 1974 he
received the degree of Bachelor of Science with Honors in
Zoology. In the fall of 1974 he enrolled as a graduate
student in the Department of Entomology and Nematology,
College of Agriculture, at the University of Florida, re-
ceiving the Master of Science degree in June, 1976. He
enrolled in the Department of Entomology and Nematology
at the University of Florida during the summer 1976, and
has pursued work toward the degree of Doctor of Philosophy.
He is currently a member of the Entomological Society
of America and the Florida Entomological Society.
109
I certify that I have read this study and that in myopinion it conforms to acceptable standards of scholarlypresentation and is fully adequate, in scope and quality,as a dissertation for the degree of Doctor of Philosophy.'
S. L. Poe, ChairmanProfessor of Entomology
I certify that I have read this study and that in myopinion it conforms to acceptable standards of scholarlypresentation and is fully adequate, in scope and quality,as a dissertation for the degree of Doctor of Philosophy.
W.'^Jonesssociate Professor ofAgricultural Engineering
I certify that I have read this study and that in myopinion it conforms to acceptable standards of scholarlypresentation and is fully adequate, in scope and quality,as a dissertation for the degree of Doctor of Philosophy.
D. H. HabeckProfessor of Entomology
I certify that I have read this study and that in myopinion it conforms to acceptable standards of scholarlypresentation and is fully adequate, in scope and quality,as a dissertation for the degree of Doctor of Philosophy.
C. A. Musgrave'Assistant Professor of Entomology
This dissertation was submitted to the Graduate Facultyof the College of Agriculture and to the Graduate Council,and was accepted as partial fulfillment of the requirementsfor the degree of Doctor of Philosophy.
December 1979
Dean, Graduate School
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