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28CHAPTER 2

HYMENOPTEROUS PARASITOIDS ASSOCIATED WITHBUFFALOGRASS AND THEm ROLE IN THE REGULATION OF

BUFFALOGRASS MEALYBUGS

INTRODUCTION

Over the past two to three decades, increased awareness of the adverse effect that

pesticides may have on the environment has underscored the need to develop alternative

methods of controlling turfgrass pests and diseases. This concern has prompted renewed

interest in biological control as an alternative and complimentary management approach

for reducing pest populations.

The biological control of arthropod pests has received considerable attention over

the past 70 years, with successful results reported in more than 60 countries around the

world (DeBach 1964). Biological control is defined by DeBach (1974) as the regulation

by natural enemies of another organism's population density at a lower average than

would otherwise occur. The major advantages of biological control are the protection of

food, fiber, and ornamental plants; the elimination of harmful effects on non-target

organisms, ground water and the environment; and economic savings (DeBach 1974).

Three approaches for implementing biological control are importation (classical),

augmentation, and conservation of natural enemies. Importation is the introduction and

establishment of exotic natural enemies into a new environment. Augmentation involves

the release of natural enemies when existing natural enemy populations are scarce.

29Conservation of natural enemies employs management practices to conserve existing

natural enemy populations (DeBach 1974).

A review of the literature reveals many situations in which reductions of serious

insect pests has been accomplished through the use of natural enemies. For example, the

parasitoid fly, Cryptochaetum iceryae (Will) was effectively utilized in the late 1800's to

control the cottony-cushion scale, Icerya purchasi (MaskelI) in California (DeBach

1974). The cassava mealybug, Phenacoccus manihoti (MatHe-Ferrero) was controlled

folIowing the introduction of the parasitoid wasp, Epidinocarsis lopezi (De Santis)

(Neuenschwander et at. 1989).

In 1913, the citrophilus mealybug, Pseudococcusfragilis (Brain) was first

observed on citrus in southern California. This mealybug became a major pest of citrus

trees and ornamentals in California. Unfortunately, no one knew exactly how this

destructive pest arrived in California. Insecticides were ineffective for controlling the

citrophilus mealybug. Eventually, two parasitoids of P. fragilis were identified in

Sydney, Australia and introduced in California. Within two years of release of

Coccophagus gurneyi Compere and Tetracnemus brevicornis (Girault), P. fragilis control

was achieved (Compere and Smith 1932).

The coffee mealybug, Planococcus kenyae (LePelIey) ilIustrates the importance

of correct taxonomic identification of the target pest for successful biological control. P.

kenyae was first found in the Thika district of Kenya in 1923 when an outbreak occurred

on coffee. This mealybug was misidentified as the citrus mealybug. Attempts to control

the pest with a parasitoid of the citrus mealybug were ineffective. Later, this mealybug

was correctly identified as the coffee mealybug. Three additional parasitoids were

30

subsequently introduced and became established. By 1941, damage was reduced and

yields had increased substantially (LePelley 1943).

In 1939 and 1940, insecticides were used in an attempt to control the citriculus

mealybug, Pseudococcus citriculus (Green) in Israel; however, none of the oil sprays or

insecticides applied provided successful control of this serious pest. Citriculus mealybug

populations were eventually controlled with the introduction of the parasitoid, Clausenia

purpurea Ishii from Japan (Rivnay 1968).

In the late 1930's and early 1940's the comstock mealybug, Pseudococcus

comstocki (Kuwana) was accidently introduced into the United States and became a

destructive pest in apple, pear, and peach orchards. Again, insecticides were ineffective,

so three parasitoids of this pest were collected from Japan and introduced into the United

States. Successful control of P. comstocki resulted within a few years after importation

of the parasitoidsAJ/optropa burrelli Muesebeck, Pseudaphycus malinus (Gahan), and

Clausenia purpurea Ishii (Haeussler and Clancy 1964).

The rhodesgrass mealybug, Antonina graminis (Maskell) emerged as a serious

pest of rhodesgrass, Chloris gayana Kunth from 1942 through the early 1950's. Control

with insecticides again proved ineffective and non-economical. In 1957 the parasitoid,

Neodusmetia sangwani (Rao) was found parasitizing rhodesgrass mealybugs in India and

was imported to the United States. By 1959 N sangwani populations were established

where rhodesgrass mealybugs were present. Ultimately, control of the rhodesgrass

mealybug was achieved following introduction of this parasitoid (Schuster et al. 1971).

Luck et al. (1988) reviewed a number of techniques for evaluating the

effectiveness of natural enemies. Paired comparison tests are a standard approach for

31

evaluating a natural enemy's effectiveness in regulating a pest population. Exclusion or

inclusion techniques involve initial elimination and continued physical exclusion of the

predator or parasitoid from one of two sets of cages. The use of cages and other barriers

for evaluating the effectiveness of natural enemies was first demonstrated by Smith and

DeBach (1942), they used paired sleeve cages to document control of the black scale,

Saissetia o/eae (Olivier) by the introduced parasitoid, Metaphycus he/vo/us Compere.

This study effectively demonstrated that fewer scale insects survived in the cages

containing both scales and parasitoids.

From 1988 to 1990 studies were conducted at the University of Nebraska-Lincoln

to survey the arthropod community associated with buffalograss. Two grass-feeding

mealybugs, Tridiscus sporoboli and Trionymus sp. which were first observed in

buffalograss evaluation plots at the John Seaton Anderson Turfgrass and Ornamental

Research Facility (JSA Facility) near Mead, NE in 1988, had caused extensive turf

damage by 1989 (Baxendale et aI. 1994). In 1990, however, only low numbers of

mealybugs could be detected in these same evaluation plots. It was speculated at the time

that the dramatic decline in mealybug levels could have been due to large numbers of

parasitoid wasps observed in these evaluation plots in 1990. At the time, these

parasitoids were not identified beyond family and little information was gathered

regarding their host preferences and seasonal activity. This information would be

important for the development of a biological control program for the pests associated

with buffalograss.

The objectives of this research were to identify the hymentoperous parasitoid

complex associated with buffalograss, identify parasitoids of Tridiscus sporoboli

32(Cockerell) and Trionymus sp., and evaluate the effectiveness of these parasitoids as

biological control agents for buffalograss mealybugs.

MATERIALS AND METHODS

Seasonal Abundance of Hymenopterous Parasitoids Associated with ButTalograss

1995 Survey ofParasitoids - The composition and seasonal abundance of

parasitoids associated with buffalograss was investigated by collecting and identifying

parasitoids from buffalograss evaluation plots at the JSA Facility near Mead, NE. Yellow

sticky traps (15 X 30 cm) were used to monitor the hymenopterous parasitoids (Bridges

and Pass 1969, Dowell and Cherry 1981, Neuenschwander 1982, and Heng~Moss et al.

1997). Traps were constructed by rolling the sticky strip into a cylinder, then stapling it

to a 30 cm wooden stake.

Ten yellow sticky traps were placed in a mealybug infested buffalograss

evaluation plot (Site 1). Traps were placed in buffalograss selections where large

numbers of mealybugs (Mean = 54.3 /230 cm2) were collected in 1994. Every 14 d,

traps were collected and replaced with new traps. Collected traps were returned to the

laboratory for processing. Monitoring started on May 23, 1995 and continued through

October 26, 1995. Parasitoid wasps and male mealybugs sticking to each trap were

identified and counted. Since large numbers of parasitoids were captured on sticky traps

it was prohibitively labor intensive to identify and monitor all collected parasitoids;

therefore, only potential mealybug parasitoids captured in relatively large numbers during

the first 2 sampling periods were recorded throughout the remainder of the season.

33

1996 Survey ofParasitoids - Parasitoids associated with buffalograss were again

monitored in 1996 from the previously described buffalograss evaluation plot (Site 1) to

identify additional parasitoids, and collect seasonal abundance information on specific

parasitoids. Parasitoid wasps were surveyed from May 21, 1996 to October 23, 1996.

Traps were removed and replaced as described for the 1995 surveying season.

Sticky traps were also placed in a second mealybug infested buffalograss plot

(Site 2) at the JSA Facility near Mead, NE in 1996. The second site provided an

additional opportunity to identify parasitoids associated with buffalograss and gather

information on their seasonal abundance. Sticky traps were placed in locations within the

evaluation plot where large numbers of mealybugs (Mean = 21 / 230 cm2) had been

collected in 1995. Ten sticky traps were placed in this evaluation plot beginning on May

21, 1996, and were replaced every 14 d thereafter until October 23, 1996.

1995 - 1996 Seasonal Abundance of the BufTalograss Mealybug and Rhopus

nigroclavatus - As mentioned earlier, mealybugs which were first observed in

buffalograss evaluation plots at the JSA Facility, near Mead, NE had caused extensive

turf damage by 1989. However, by 1990 only low numbers of mealybugs could be

detected in the same plots. Baxendale et al. (1994) speculated that parasitoid wasps may

play an important role in the regulation of mealybug infestations in the field. The

objective of this study was to determine ifthere is a relationship between the seasonal

abundance patterns of these parasitoid wasps subsequently identified as Rhopus

nigroclavatus and the buffalograss mealybug. Seasonal abundance information on R.

nigroclavatus and male mealybugs was obtained from the' 1995 and 1996 Survey of

Parasitoids' studies described above.

34

Parasitoids Associated with BufTalograss Mealybugs - The parasitoid complex

associated with the buffalograss mealybug was documented in 1996 by conducting a

series of 5 rearing and 4 dissection studies (Day 1994). These two approaches served to

identify mealybug parasitoids and evaluate levels of parasitism. Initially, mealybugs

were collected from buffalograss evaluation plots at the JSA Facility near Mead, NE.

Collected mealybugs were then reared in the greenhouse on pots ofNE 85-97, a

mealybug susceptible buffalograss selection (Johnson-Cicalese 1995).

Rearing Studies - In the rearing studies, adult female mealybugs were collected

from the leaf sheaths of infested buffalograss clippings. For studies 1,2, and 3,50 adult

female mealybugs were collected; and for studies 4 and 5, 100 adult female mealybugs

were collected. Parasitoids were reared from mealybugs in small (1 oz.) plastic cups in

the laboratory.

Dissection Studies - Four dissection studies were conducted to detect and

identify internal parasitoids of buffalograss mealybugs. One hundred mealybugs from

each three age groups (1st and 2nd instars, 3rd and 4th instars, and adult females) were

collected and dissected for each study.

Evaluation of Mealybug Parasitoids as Potential Biological Control Agents -

Tubular cages of clear acetate, 12 cm in diameter by 30 cm high were used as a barrier

for exclusion of parasitoid wasps. Cage tops were covered with organdy fabric. Plants

were started from Texoka seed to ensure initial freedom from mealybugs and parasitoids.

Plants were maintained in a greenhouse at the University of Nebraska East Campus,

Lincoln, NE, and were caged to prevent accidental mealybug and/or parasitoid

contamination. Once the seedlings were well established, plants were inoculated with 40

35nymphal mealybugs to initiate a mealybug infestation. Since parasitoids prefer to

parasitize late instar (3rd and 4th) nymphs and adult female mealybugs (See Chapter 3),

plants were inoculated with early instar (1st and 2nd) mealybug nymphs to reduce the

likelihood of introducing previously parasitized mealybugs.

Pots were randomly assigned to one of2 treatments: cages containing only

mealybugs (MB only), and cages containing both mealybugs and parasitoids (MB +

Para). At the start of the experiment, 3 parasitized female mealybugs (See Chapter 3)

were introduced into the cages of the MB + Para treatments. Parasitized female

mealybugs were introduced rather than adult parasitoids because of the difficulty

associated with transferring active adult wasps. The study was repeated two times.

Treatments were arranged in a completely randomized design with 6 replications,

except for Study 2 which had 4 replications. Plants were harvested 4 wk after the

introduction of the parasitized female mealybugs. Every buffalograss tiller in each 15 cm

pot was examined and the number of parasitized and non-parasitized (healthy) mealybugs

recorded.

RESULTS AND DISCUSSION

Seasonal Abundance of Hymenopterous Parasitoids Associated with ButTalograss

1995 and 1996 Survey of Parasitoids - Numerous parasitoids were captured on

sticky traps during the two years sampled (Table 2.1). Families of parasitoids collected

included Scelionidae, Encyrtidae, Mymaridae, and Trichogrammatidae. Scelionids,

Mymarids, and Trichogrammatids are all parasitoids of insect eggs; whereas, Encyrtids

are generally endoparasites of Hornoptera, but have been reported as egg parasitoids

36

(Goulet and Huber 1993). Mymaridae A (unidentified species), Trichogramma A

(unidentified species), and Rhopus nigroclavatus were the most abundant parasitoids

collected at both sites during the 1995 and 1996 season. These represented 79% of the

total hymenopterous parasitoids collected (Table 2.1).

Overall Mymaridae A was the most abundant hymenopterous parasitoid collected

during the 1995 and 1996 seasons (Table 2.1). The greatest numbers ofMymaridae A

were collected from June to September from Site 1 (Figure 2.1). Consistently more

Mymaridae A were collected during 1996 than in 1995.

Trichogramma A was also well represented throughout the two years sampled at

Site 1 (Table 2.1). In contrast to Mymaridae A, the greater numbers of this parasitoid

was collected in 1995. Parasitoid numbers were highest from July to September

indicating that this parasitoid is most abundant during mid-season (Figure 2.2).

Large numbers of R. nigroclavatus (Family: Encyrtidae) were also collected on

sticky traps during the 1995 and 1996 seasons (Table 2.1). The abundance of R.

nigroclavatus steadily increased throughout both seasons, counts were highest during

July, August, September, and October (Figure 2.3). Substantially more R. nigroclavatus

were collected during the 1996 season than during the 1995 sampling period.

In general, the seasonal abundance of the remaining six parasitoid groups

monitored were dramatically different from year to year (Figure 2.4 - 2.9). It is difficult

at this point to determine the reasons for the fluctutations in parasitoid population levels

until the hosts of these parasitoids are identified, since the abundance and seasonal

distribution of a parasitoid is normally dependent on the seasonal abundance of the host.

The information gained from this study however provides baseline information on the

37

parasitoids associated with buffalograss. Further research is needed which focuses

specifically on the hosts of these parasitoids and the role these parasitoids play in

regulating insect pests in buffalograss.

1995 - 1996 Seasonal Abundance of the BufTalograss Mealybug and Rhopus

nigroclavatus - Sticky trap field data (Table 2.1 and Figure 2.3) collected in 1995 and

1996, from Site 1 documented the presence of large numbers of R. nigroclavatus

associated with mealybug infested buffalograss. The large number of R. nigroclavatus

collected on the sticky traps suggests that these parasitoids may be playing an important

role in regulating mealybug infestations.

Male mealybugs captured on sticky traps steadily increased from May to July in

1995, then decreased throughout the remainder of the season (Figure 2.10). The number

of collected R. nigroclavatus remained relatively low throughout the 1995 season (Figure

2.10). Both male mealybugs and R. nigroclavatus populations dropped to low levels in

October which likely reflects the onset of freezing temperatures.

While male mealybug numbers were much higher than R. nigroclavatus during

the 1995 season, the opposite was observed in 1996. Male mealybugs were dramatically

reduced when compared to the previous year; whereas, parasitoid levels were

substantially higher (Figure 2.11).

Although little has been published on the sex ratios of Tridiscus sporoboli and

Trionymus sp., near 1:1 ratios are common for some mealybug species (James 1937).

James also noted that the sex ratio varied from 1:1 to 1 male: 5 females among five

species of mealybugs studied. Assuming that the sex ratio is 1:1 for T. sporoboli and

38

Trionymus sp., 800 male mealybugs which were collected in July 1995 on the sticky

traps, may represent a substantial mealybug population.

The data collected from 1994 - 1996 suggests that the decline of mealybugs may

have been due to the increase of R. nigroc/avatus. The fluctuations in the population

levels of the mealybugs from 1994 to 1996 were similar to the mealybug population

levels found by Baxendale et aI. (1994). In both cases, the natural regulatory effect of R.

nigroc/avatus may have been responsible for the decline in the mealybug population

levels.

Parasitoids Associated with BufTalograss Mealybugs - Parasitoid wasps

identified as Pseudaphycus sp. and Rhopus nigroc/avatus (Ashmead) (Family:

Encyrtidae) (Both identified by Dr. John Noyes at the Nat. Hist. Mus. - London) were

reared and dissected from buffalograss mealybugs.

Encyrtids represent one of the largest and most diverse chalcidoid families. Many

encyrtids are endoparasites of Coccoidea and Pseudococcidae (Homoptera), but also have

been recorded as parasitoids of many other insect orders (Noyes and Hayat 1994).

Limited information is available in the literature on the genus Pseudaphycus. The

incidence of Pseudaphycus sp. was very low (less than 10%) in both 1995 and 1996.

Accordingly, research presented in this chapter and Chapter 3 focused on evaluating R.

nigroc/avatus as a biological agent for buffalograss mealybugs. It will be essential in the

future, however, to learn more about Pseudaphycus sp. particularly relative to its biology,

distribution, and the potential regulating effect on T. sporoboli and Trionymus sp.

R. nigroclavatus has previously been recorded as a parasitoid of Pseudococcus

saccharifolii (Green), Pseudococcus calceolarie (Maskell), Saccharicoccus sacchari

39

(Cockerell), and Pseudococcus boninsis which are all mealybug pests of sugarcane

(Fullaway 1920, Timberlake 1924, Williams 1931, Box 1953, and SubbaRao 1960). In

addition, R. nigroclavatus has also been identified as a parasitoid of Ripersia sp. on grass

(Noyes and Hayat 1994). R. nigroclavatus has been collected in Spain, India, Nepal,

Malaysia, Australia, and Hawaii indicating the widespread distribution of this species.

High rates of parasitism were recorded from the rearing and dissection studies

(Table 2.2 and 2.3) suggesting R. nigroclavatus can effectively reduce mealybug

populations below damaging levels, at least under greenhouse conditions.

Rearing Studies - The overall rate of parasitism for adult female mealybugs for

the 5 studies conducted over the 5 month period averaged 48.6% (Table 2.2). A

maximum of seven parasitoids were reared from a single reproductive female mealybug.

Similar rates of parasitism of adult female mealybugs by R. nigroclavatus were observed

in no-choice studies (See Chapter 3). Only adult female mealybugs were included in

these studies due to the difficulty of rearing early instar (1st and 2nd) mealybug nymphs.

Dissection Studies - Dissection studies (Table 2.3) documented parasitism of

immature and female mealybugs. Average rates of parasitism for the adult female, 3rd

and 4th instar nymphs, and 1st and 2nd instar mealybugs were 78.5%, 67.5%, and 4.25%,

respectively for the 4 studies over the 4 month period of testing. These studies clearly

demonstrated R. nigroclavatus preference for adult female mealybugs and 3rd and 4th

instar nymphs. Additional information on the ovipositional preference of R.

nigroclavatus is discussed in Chapter 3.

These studies indicate the potential for R. nigroclavatus to be an effective

biological control agent for buffalograss mealybugs under greenhouse conditions. The

40

release of this parasitoid in greenhouses where mealybug populations are high may be an

effective technique for reducing pest populations and eliminating potential undesirable

side effects associated with pesticides.

Evaluation of Mealybug Parasitoids as Biological Control Agents - Paired

comparison tests conducted in the greenhouse documented the effectiveness of R.

nigroclavatus as a biological control agent for buffalograss mealybugs.

Study 1- Significant differences were detected (T = 2.28; df= 10,0; P < .0452) in

the number of non-parasitized (healthy) mealybugs between the MB only (Mean = 61.5)

and the MB + Para (Mean = 13.2) treatments (Table 2.4). Due to the high level of R.

nigroc1avatus parasitism, the MB + Para treatments never developed heavy mealybug

infestations. The ability of this parasitoid to locate and parasitize a mealybug host was

further demonstrated when, despite best efforts to exclude them, parasitoids managed to

enter and contaminate the MB only pots resulting in a mean parasitism rate of 0.3%. The

mean rate of parasitism for the MB + Para treatments was 73.33%.

Study 2 - Total numbers of non-parasitized (healthy) mealybugs were

significantly different (T = 6.52; df= 3,2; P < .0064) between the MB only (Mean = 32.3)

and the MB + Para (Mean = 2.3) treatments (Table 2.5). The mean rate of parasitism for

the MB + Para treatment pots was 83.8%, again the efficient searching behavior of

Rhopus resulted in 2.15% parasitism in the MB only treatment pots. These studies again

demonstrated the regulating potential of R nigroc1avatus on mealybug populations.

41

CONCLUSIONS

The successful control of buffalograss mealybugs depends on the development of

effective, alternative pest management strategies since mealybugs are notoriously

difficult to control by conventional chemical means. Rearing and dissection studies of

buffalograss mealybugs identified Rhopus nigroclavatus and Pseudophycus sp. as

parasitoids of Tridiscus sporoboli and Trionymus sp. At the present time, these two

parasitoids, particularly Rhopus, offer the most potential as biological control agents for

mealybug populations. Success in biological control is dependent on a thorough

understanding of the pest, its natural enemies, and their interactions. Studies to obtain

information on the biology, ecology, and life history of the pest and its natural enemies

are therefore an essential component of a successful biological control program.

Besides R. nigroclavatus and Pseudaphycus sp., several other parasitoids (See

Table 2.1) were collected from buffalograss. Unfortunately, little information is available

on the biology, hosts, distribution, and life history of these parasitoids. Further research

is needed to identify the hosts of these parasitoids.

Previous research by Dicke (1937) identified a Scelionid wasp, Eumicrosoma

benefica Gahan as an egg parasitoid of the hairy chinch bug. Research should be

undertaken to determine if the Scelionid wasp, Eumicrosoma sp. which was collected on

the sticky traps is a parasitoid of the buffalograss chinch bug. If so, this parasitoid wasp

could possibly be used as a biological control agent to regulate another serious insect pest

of buffalograss.

Buffalograss is grown in the greenhouse year round for vegetative propagation

and research purposes. Many times the buffalograss is field collected and is infested with

42mealybugs and/or other arthropod pests which are then introduced into the greenhouse.

Attempts to control the mealybugs with insecticides have been largely unsuccessful under

greenhouse (and field) conditions. This research has demonstrated the regulatory

potential R. nigroclavatus has on mealybug populations under greenhouse conditions. R.

nigroclavatus has the potential to be used extensively in the greenhouse for augmentive

control of buffalo grass mealybugs.

Although this research has shown that R. nigroclavatus can be a very effective

parasitoid of buffalograss mealybug populations under greenhouse conditions, studies to

evaluate this parasitoid as a biological control agent for buffalograss mealybugs under

field conditions needs to be undertaken. The evaluation of R. nigroclavatus as a

biological control agent for mealybug field populations will be very challenging because

it is difficult to establish an infestation in the field because of the effectiveness of

mealybug parasitoids. The effectiveness of these parasitoids could be evaluated in the

field if steps are taken initially to exclude parasitoids from the mealybug infested plots.

The success of a biological control program ultimately relies on the effectiveness

of the natural enemy. The qualities most important for the effectiveness of a parasitoid in

pest population regulation include a high reproduction rate, good searching ability, host

specificity, ability to synchronize lifecycle with their host, and adaptability and tolerance

to a broad range of environmental conditions. These studies have demonstrated that R

nigroclavatus is an effective parasitoid of the buffalograss mealybug. Conservation of

naturally occurring R nigroclavatus populations probably represents the most readily

available approach for the implementation of a biological control program for

buffalograss mealybugs. However, inoculative release ofthis parasitoid may be

43

appropriate when R. nigroclavatus populations are low in the field. Further research is

needed to develop effective techniques for the mass rearing and release of this parasitoid.

Biological control provides an attractive, alternative approach for regulating

mealybug pest populations in buffalograss. The results from these studies suggest the

potential of R. nigroclavatus to maintain mealybug populations below damaging levels.

Presently, the adoption of a biological control program may offer the most effective

management strategy available for reducing buffalograss mealybug populations.

Table 2.t. Seasonal abundance of Hymenopterous parasitoids associated with bufTalograss at two locations.

19951 19962 Total % of TotalSite 1 Site 2

Mymaridae A 634 2220 2316 5170 34.96

Tr;cho~.T:rammaA 2377 745 520 3642 24.63

Rhoplls 328 1309 1249 2886 19.511/;Krocla\,atlls

Tr;chogramma B 275 173 234 682 4.61

Mymaridae B 213 247 189 649 4.39

Encyrtidae 265 97 161 523 3.54

Scelionidae 98 134 178 410 2.77

Mymaridae C 312 15 12 339 229

Mymaridae 0 75 98 70 243 1.64

1 Number of parasitoids collected from a butTalograss evaluation plot at the JSA Facility (Site 1) near Mead, NE.

2 Number ofparasitoids collected from two butTalograss evaluation plots at the JSA Facility (Site 1 and Site 2)near Mead, NE

700

600

500

400.8E

IJ1995::Iz300 .1996

200

100

0May June July Aug Sept Oct

Date

Figure 2.1. Seasonal abundance of Mymaridae A collected from Site 1 at the JSA Facility during1995 and 1996.

800

700

600

500....8 400E:::JZ

300

200

100

0May June July Aug

DateSept Oct

01995

.1996

Figure 2.2. Seasonal abundance of Trichogramma A collected from Site 1 at the JSA Facility during1995 and 1996.

June July

DateAug Sept Oct

Figure 2.3. Seasonal abundance of Rhopus nigroclal'atus (Family: Encyrtidae) collected from Site I at theJSA Facility during 1995 and 1996.

OctSeptAugJulyJuneo

20

100

80

~.8

60E~C 1995z.1996

40

Date

Figure 2.4. Seasonal abundance of Trichogramma B collected from Site 1 at the JSA Facility during1995 and 1996.

01995.1996

80

70

60

50...8 40E::lZ

30

20

10


Date

Figure 2.5. Seasonal abundance of Mymaridae B collected from Site 1 at the JSA Facilityduring 1995 and 1996.

70 I

60

50

40~E

[J 1995::lz30

.1996

20

10


Date

Figure 2.6. Seasonal abundance of Encyrtidae collected from Site I at the JSA Facility during1995 and 1996.

VIo

45

40

35

30

j 25E::IZ 20

15

10

5

0May June July Aug

Date

01995

.1996

Sept Oct

Figure 2.7. Seasonal abundance of Scelionidae collected from Site 1 at the JSA Facility during1995 and 1996.

80

70

60 II

50

! 40E::JZ

30

20

10

olMay June July Aug

Date

01995.1996

.~I~.

Sept Oct

Figure 2.8. Seasonal abundance of Mymaridae C collected from Site 1 at the JSA Facility during1995 and 1996.

VoN

45

40 /

35

30

.. 25.!E:::lZ 20

151

10

5


Date

[]1995.1996

Figure 2.9. Seasonal abundance of Mymaridae D collected from Site 1 at the JSA Facilityduring 1995 and 1996.

'JIW

900

800

700

600..Q,j 500-=E= 400Z

300

200

100


Date

-+- Male Mealybugs

__ R nigroclavatus

54

Figure 2.10. Relative abundance of male mealybugs and Rhopusnigroclavatus as sampled by sticky traps during 1995from Site 1.

400

350

300

.. 250QJ

,/:).e 200=Z 150

100

50


Date

-+-Male Mealybugs

__ R nigroclavatus

Figure 2.11. Relative abundance of male mealybugs and Rhopusnigroclavatus as sampled by sticky traps during 1996from Site 1.

Table 2.2 Rates of adult female mealybugs parasitism by Rhopus n;groclavatus determinedby rearing studies.

Non-Parasitized Parasitized PercentMealvbu2s Mealvbu2s Parasitism

Study 1 24 26 52

Study 2 31 19 38

Study 3 22 28 56

Study 4 57 43 43

Study 5 46 54 54

Table 2.3. Parasitism by Rhopus nigroclavatus for all age groups of mealybugs determinedby dissection studies.

Non-Parasitized Parasitized PercentMealvbu2s Mealvbu2s Parasitism

Study 11st/2nd 95 5 53rd/4th 57 43 43Female 30 70 70




Table 2.4. Pairfil comparison Study 1 conduCCfil to n-aluate the efTKtinness of Rltoplls IIigroclavahlS as abiological control agent of Tridisclls sporoboIi and TriollY,""s sp.

M8 Only I M8+Para1

./. Parasitism e;'. ParasitismNpJ p. M8 Only ~P P M8 + Para

Rep I 55 0 0 0 9 100

Rep 2 18 0 0 5 14 74

Rep 3 62 0 0 67 ~., 44

Rep 4 15 0 0 3 8 73

Rep 5 85 12 92

Rep 6 \34 .. 3 4 57-Mun 61.5 OS 03 13.2 165 73 3

I The treatment isolatin~ on1\ mea1\bulls~The treatment isolating both meal~bugs and parasitoids, NP = Non-parasitized (Health\) mealybugs4 poc Parasitized mealybugs

Table 2.5. Paired comparison Study 2 conducted to evaluate the effectiveness of Rhopus n;groclavatus as abiological control agent of Trid;scus sporoboli and Trionymus sp.

MBOnlv1 MB+ Para 2

% Parasitism % ParasitismNpl p4 MBOnly NP P MB+ Para

Rep 1 22 0 0 0 26 100

Rep2 31 0 0 2 8 80

Rep 3 44 0 0 4 23 85

Rep4 32 3 8.6 3 7 70

Mean 32.3 .75 2.15 2.3 16 83.8

I The treatment isolating only mealybugs.2 The treatment isolating both mealybugs and parasitoids.3 NP = Non-parasitized (Healthy) mealybugs.4 P = Parasitized mealybugs.

hymenopterous parasitoids associated with …archive.lib.msu.edu/tic/thesdiss/heng-moss1997c.pdf ·...

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