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SELECTIVE PESTICIDES AND BIOLOGICAL CONTROL IN WALNUT

PEST MANAGEMENT

N.J. Mills, K. Mace-Hill, L. Jones, R.A. van Steenwyk, C. Pickel, and J. Grant

ABSTRACT

In recent years we have seen dramatic changes in the pest management tools available for use in

walnuts, mostly driven by Food Quality Protection Act -mandated reductions in organophosphate

(OP) use. Codling moth as the key pest of walnuts has traditionally been controlled by multiple

sprays of OPs applied within season. While the development of new approaches for the use of

pheromone-based mating disruption shows promise as an effective alternative to insecticides

only, new ‘reduced risk’ products are replacing the more traditional OPs. These ‘reduced risk’

products are not always compatible with natural enemies and can lead to disruption of the

biological control of secondary pests such as the walnut aphid and spider mites. The goal of this

project is to screen new pesticides to identify selective products that will enhance the level of

biological control in walnut orchards as part of a larger western regional USDA-SCRI project

(http://enhancedbiocontrol.org).

From bioassays of some of the more recently registered pesticides in walnuts, it appears that

pyrethroids, spinosyns and some diamides can be toxic to the key natural enemies of walnut

aphids and spider mites and so have the potential to be disruptive of biological control. Of the

products tested, Warrior and Delegate have shown some of the strongest effects using simple

laboratory bioassays with the parasitoid Trioxys pallidus and the predator Hippodamia

convergens, and are predicted to have effects that would be apparent in the field. Our research

trials to verify these effects under field conditions in commercial walnut orchards have been

compromised by unusually cool spring weather during the past two years that resulted in very

low populations of both walnut aphid and spider mite. While no effects on predatory mite control

of spider mites could be detected, the use of Delegate resulted in increased aphid populations in

both 2010 and 2011 with a corresponding decline in the extent of parasitism by T. pallidus. Our

laboratory and field research also suggests that Altacor as a codling moth treatment could

selectively enhance the impact of biological control, although another diamide Cyazypyr showed

greater toxicity to a broad range of natural enemies.

Results from the larger USDA-SCRI project indicate similar toxic effects of Warrior and

Delegate for other key natural enemy species in western orchards, and suggest that herbivore-

induced plant volatiles can be used as an effective tool to monitor the activity and flight periods

of a range of key natural enemies in orchards, such as parasitoids, syrphids and green lacewings.

California Walnut Board 231 Walnut Research Reports 2011

INTRODUCTION

In recent years we have also seen dramatic changes in the pest management tools in walnuts

driven in part by Food Quality Protection Act -mandated reductions in organophosphate (OP)

use, and in part due to water quality issues. Codling moth as the key pest of walnuts has

traditionally been controlled by multiple sprays of OPs applied per season. While the

development of new approaches to the use of pheromone-based mating disruption shows promise

as an alternative to reliance on insecticides, new ‘reduced risk’ insecticides are replacing the OPs.

The latter are likely to remain an important tool in the management of codling moth, but their

impacts on natural enemies are poorly understood and often much greater than might be

expected. Information developed by participants in a western regional USDA-SCRI grant

suggests that we may be creating unstable management programs because of the negative effects

of some of the newer pesticides on natural enemy populations. Disruption of the biological

control of secondary pests by natural enemies through use of these new ‘reduced risk’ products

can lead to a reliance on pesticides for suppression of secondary pests that is costly both

economically and ecologically, and is detrimental to worker safety. To remain competitive, stable

IPM programs that effectively conserve natural enemies must be developed as even a small

increase in natural enemy induced-mortality significantly lowers potential pest pressure.

The walnut aphid, Chromaphis juglandicola (Kaltenbach) has been known in California for more

than 100 years. When present in large number in the spring, aphid feeding reduces tree vigor, nut

size and quality. During the summer, it induces a shriveling of the kernels before harvest.

Extremely high populations of aphids may lead to leaf drop, exposing nuts to sunburn. The

introduction of the parasitic wasp Trioxys pallidus (Halliday) from Iran in 1969 led to a dramatic

success in the biological control of walnut aphid populations in California, and has provided

sustained control of this devastating pest for the past 39 years. However, both growers and PCAs

have noted that aphid outbreaks, though not consistent, are of increasing concern in the Central

Valley with in-season spray treatments required in some cases. As pest management practices in

walnuts change to both reduce costs and make use of new pesticides, it is important to retain the

benefits of the long-term biological control of walnut aphid provided by the introduction of T.

pallidus.

The goal of this project is to screen new pesticides to identify selective products that will

enhance the level of biological control in orchards as part of a larger western regional USDA-

SCRI project (http://enhancedbiocontrol.org). Other collaborators in the larger project will be

screening a broader range of natural enemy species to build a more comprehensive picture of the

selectivity of new ‘reduced risk’ pesticides that could disrupt the natural enemy control of other

pests such as codling moth and spider mites. An additional benefit of participation in the larger

regional project is that the latter also includes research on the use of herbivore-induced host plant

volatiles to both monitor the seasonal phenology of natural enemy flights and develop an

effective tool for growers and PCAs to use in assessing the activity of natural enemies in western

orchards.testicides on natural enemies. Laboratory bioassays are used to estimate both acute and

sublethal effects of pesticides on walnut aphid, T. pallidus and its dominant hyperparasitoid

Syrphophagus aphidivorus, and on the generalist aphid predator Hippodamia convergens. The

outcomes of these laboratory bioassays are then verified through replicated field trials in

commercial walnut orchards.


OBJECTIVES

The general objective is to better understand the impact of newer pesticides used for the

management of primary pests in walnuts, such as codling moth, on secondary pests, such as the

walnut aphid, one of the best examples of an effective biological control in western orchards. The

specific objectives are:

1. To assess the differential susceptibility of T. pallidus, S. aphidivorus and H.

convergens to walnut pest management products using simple laboratory

bioassays.

2. To use a demographic bioassay to test a subset of pest management products for

their compatibility with and enhancement of biological control of walnut aphid.

3. To verify the impact of pesticides identified as disruptive from the laboratory

bioassays through large block replicated field trails in walnut orchards.

PROCEDURES

Objective 1. To assess the differential susceptibility of T. pallidus, S. aphidivorus and H.

convergens to walnut pest management products using simple laboratory bioassays

This year laboratory assays were used to determine the potential disruptive effects of pest

management products on the survivorship of adult Trioxys pallidus and Syrphophagus

aphidivorus, and of both larval and adult H. convergens exposed to surface residues. Products

tested included those currently registered in walnuts either for codling moth, husk fly or aphids

including the insecticides Warrior (pyrethroid), Altacor and Cyazypyr (diamides), Delegate

(spinosyn), Rimon (IGRs), and the fungicides sulfur (Kumulus) and Kocide-Manzate. A full

strength solution (100% field rate) was used to represent the concentration that the natural

enemies would experience at the time of application, a dilute solution (10% field rate) was used

to represent the possible concentration that they would be exposed to after field weathering, and

these were both compared to water (0% field rate) as a control. The full field rates of these

products are shown in Table 1. Glass vials (8 x 2.5 cm) were filled with pesticide solutions and

then drained and dried to provide a consistent residue on the inner surface. Similarly, small

droplets of a honey-sugar-agar-water mixture (10-1-1-100 ratio) were used as food for the adult

wasps and treated by dipping in insecticide solutions to gain a surface coating of residue. For the

wasps, a male and female pair of 1-2 day old adults were placed into a treated glass vial,

provided with treated food, and held at 22°C and 16h daylength. For H. convergens, individual

2nd

instar larvae and 4 day old adult females were placed into treated glass vials, and provided

with untreated 3rd

instar aphids as food. From 10-20 replicate vials were used for each natural

enemy species and pesticide combination, and survivorship was monitored after 48h.

The acute mortality in each replicate vial was analyzed separately for the each natural enemy

species and survivorship data from the full field rate and dilute rate were corrected for control

mortality using Abbott’s correction. Following Dorfman et al. (1980, Regulating Pesticides, NAS

Press), 95% confidence intervals were calculated from a second order approximation of the

maximum likelihood variance.


Objective 2. To use a sublethal demographic bioassay to test a subset of pest management

products for their compatibility with and enhancement of biological control of walnut aphid

For those pesticide products that did not show high acute toxicity at the 10% field rate, sublethal

bioassays were also carried out for both T. pallidus and H. convergens. Unlike traditional

pesticides that frequently caused acute toxic impacts on natural enemies, the newer classes of

pesticides tend to have greater impacts on life history performance than on survivorship. These

effects can often be equally important in reducing the abundance of natural enemies in orchards

and are best evaluated using specifically designed sublethal bioassays. A control and a single

concentration of each product were compared in the sublethal bioassays, the single concentration

corresponding to the greater of the two concentrations used in the acute bioassay that killed less

than 70% of the experimental natural enemies.

As a bioassay arena for T. pallidus, a glass cylinder of 2.6cm height by 2.4 cm diameter was

sprayed with 1.95 mL of test solution in a Potter tower, turned over, and sprayed with 1.95 mL of

solution again, resulting in residue deposit of 1.5 mg cm-2

. When dry, these cylinders are used to

make clip cages to attach to walnut leaves on a potted seedling plant. For adult food for the

wasps 10 uL droplets of 50:50 honey-water solution were pipetted into a plastic-wrap-covered

petri dish and sprayed with 1.05 mL of test solution. Finally, T. pallidus adults less than 24h old

were knocked out with 5 seconds of compressed CO2 at 10 PSI, and then topically sprayed in a

Potter tower with 1.05 mL of test solution. Female-male pairs were placed in treated clip cages

on walnut seedlings with 25 3rd instar yellow walnut aphids and two streaks of treated honey

solution. After 24h, the experimental females were transferred to another treated clip cage

(treated at the same time as the original) containing a fresh set of 25 hosts and honey solution. An

untreated, slightly larger-diameter clip cage was then placed around the previous day's hosts and

followed to monitor mummy formation and adult parasitoid emergence. The experimental adults

were maintained in the sublethal assays for a period of 3 days, representing the first 40% of their

typical lifespans. The experimental insects were kept at a 16:8h light:dark photoperiod at 22°C.

Adult survivorship and daily fecundity, and progeny development time and sex ratio were noted

from these bioassays.

A similar approach was used for both larvae and adults of H. convergens, although in this case

the glass arenas were slightly larger in size and were not clipped onto leaves of walnut seedlings.

Treated diluted honey and fresh aphids were provided to both larvae and adult H. convergens and

survivorship, daily fecundity and progeny sex ratio (adult bioassays) and development time

(larval bioassays) were estimated.

Each of these life history parameters for the experimental natural enemies was compared to those

of the control individuals using ANOVA with an arcsine square root transformation for

percentage data, and log transformation for count data. As it is not intuitively obvious whether an

increase of development time would be more detrimental than a similar magnitude of decrease in

daily adult fecundity, the life history parameters were integrated into a single population-level

index of impact using a demographic model. Stage structured matrix models provide a simple

approach to translating the individual-level responses to pesticide exposure into likely effects on

populations of natural enemies in the field. The impact of each pesticide was estimated by


changing those life history parameters in the model that were significantly impacted in either the

acute or the sublethal assays.

Objective 3. To verify the impact of pesticides identified as disruptive from the laboratory

bioassays through large block replicated field trails in walnut orchards

To verify the observations from the acute and sublethal bioassays in the lab, additional replicated

field trials was carried out in 2011, similar to the one conducted in 2010. For these trials we

compared products that appear to differ in their general effects on natural enemies from the lab

bioassays – Delegate and Warrior that appear to be disruptive, and Altacor that appears to be

compatible. Two trials were carried out in a walnut orchard near Chico. The field applications

were timed for codling moth management and applied twice during each of the first two

generations. In the first trial, three replicates blocks (approximately 1 acre) of four treatments

were used; Altacor applied for the A peak followed by Delegate applied for the B peak of the

codling moth flights, the reverse of Delegate followed by Altacor each generation, a grower

standard consisting of Warrior for 1st generation and Lorsban for 2

nd generation, and a no

pesticide control. For the second trial, there were four replicates of three treatments; Altacor

applied once each generation, Voliam Xpress (Altacor plus Warrior) applied once each

generation, and a grower standard consisting of Warrior for 1st generation and Warrior plus

Lorsban for 2nd

generation. Aphids and spider mites and their associated natural enemies were

sampled at two week intervals throughout the season by collecting three compound leaves from

each of five trees in the three center rows of each plot. The abundance of aphids and their natural

enemies was counted directly from each leaflet, while the abundance of spider mites and

predatory mites were determined after removal from the foliage with a mite-brushing machine.

As the number of leaflets on the compound leaves varied through the season, the count data were

first standardized to number per leaflet before being analyzed. The cumulative season-long totals

of aphid, mite and natural enemy abundance were analyzed using ANOVA, and the seasonal

patterns were examined analyzed using ANOVA at each sample date.

RESULTS

Objective 1. To assess the differential susceptibility of T. pallidus, S. aphidivorus and H.

convergens to walnut pest management products using simple laboratory bioassays

The selected pesticides showed different effects on T. pallidus, as a key aphid parasitoid, and H.

convergens, as a key aphid predator, in the acute laboratory bioassays (Fig. 1). For example

Cyazypyr, Delegate, Warrior and Kumulus all caused substantial acute mortality of adult T.

pallidus at a full field rate, and the first two of these pesticides had a similar effect even at a

dilute 10% field rate. In contrast, Warrior had the greatest impact on both larvae and adults of H.

convergens, at both the full and dilute rates. In contrast, the acute bioassays showed little effect

of Cyazypyr, Delegate, and Kumulus on either the larval of adult stages of H. convergens. Such

differences between parasitoids and predators may be common, as shown from the results

accumulated from the broader regional project as a whole (Table 2). The woolly apple aphid

parasitoid Aphelinus mali showed a similar response to T. pallidus in the acute bioassays, being


impacted by Cyazypr, Delegate and Warrior, but not by Kumulus. In contrast, at least the juvenile

stages, if not the adult stages, of the pear psylla predator Deraeocoris brevis, the green lacewing

Chrysoperla carnea, and the spider mite predator Galendromus occidentalis were not impacted

by either Cyazypyr or Delegate in the sublethal bioassays, although all were impacted by

Warrior.

It is also important to note that from the acute bioassays, both Altacor as an insecticide, and

Kocide-Manzate as a walnut blight spray, had the least impact on the 48h survivorship of the

natural enemy species tested, with Rimon having some detrimental impacts on the juvenile stages

of predators such as D. brevis and spiders (Table 2).

Objective 2. Objective 2. To use a sublethal demographic bioassay to test a subset of pest

management products for their compatibility with and enhancement of biological control of

walnut aphid

The sublethal bioassays were used for those pesticides that proved not to be acutely toxic to T.

pallidus or H. convergens in the acute bioassays to test for potential effects that could influence

the life history performance of the wasps. The sublethal bioassays for T. pallidus have been

completed, while those for H. convergens are still in progress. For both natural enemy species,

sublethal bioassays were conducted only for those pesticides that killed less than 75% of the

experimental individuals in the acute bioassays. The reason for this is that it is not possible to

estimate sublethal impacts when the number of experimental individuals surviving for more than

48h is so low. Thus for T. pallidus the pesticides used for sublethal bioassays were Altacor,

Rimon and Kocide-Manzate at the standard field rate (1x), and Warrior and Kumulus at a 10%

field rate (0.1x). Similarly, for H. convergens all of the pesticides, with the exception of Warrior,

were used in the sublethal bioassays for both larvae and adults.

For T. pallidus, we found few sublethal effects from the pesticides bioassayed (Fig. 2). Kumulus

was the only product to affect the survivorship of female wasps, despite the inclusion of all three

routes of exposure (topical, residual and oral) in these bioassays. There were no observed effects

of the pesticides on the sex ratio of the progeny produced by adults exposed to the pesticides, but

there were some effects on daily fecundity. Altacor reduced daily fecundity by 25%, Kumulus by

64%, and Warrior by 84%. Although the sublethal bioassays for H. convergens are still in

progress it is clear that stronger effects are to be expected. For example, while both Cyazypyr and

Rimon did not cause acute mortality, they reduced larval survivorship by 80% and 100%

respectively in recent sublethal bioassays.

As it is not clear whether mortality is likely to have a greater impact on natural enemy

populations than reductions in daily fecundity, we have used stage structured matrix models to

integrate these observed effects on the life history performance of exposed individuals to a single

parameter, the population growth rate (PGR). As an overall effect, PGR represents the potential

for a natural enemy species to be able to maintain or recover its contribution to biological control

following exposure to a particular pesticide. To illustrate the probable effect of PGR on the

biological control of secondary pests in walnuts, we use population projections showing how

PGR influences the growth of a population of T. pallidus over time (Fig. 3). Thus in the absence


of exposure to pesticides T. pallidus has a PGR of 0.317 allowing its population to grow from

100 to 1000 individuals within 18 days in the absence of any other constraints. The slight

reduction in daily fecundity that results from exposure to Altacor generates a PGR of 0.279

which would delay the growth of a T. pallidus population from 100 to 1000 individuals by 2

days. In contrast, the combined acute mortality and reduction in daily fecundity caused by

exposure to Warrior, results in a PGR of 0.02, and consequently to a delay in the growth of a T.

pallidus population by 24 days. These models allow the diverse toxic effects that the pesticides

have on individuals of T. pallidus in the laboratory bioassays to be integrated and ranked in terms

of their likely population impacts on T. pallidus in the field. However, the models for T. pallidus

do not take into account the effect of the pesticides on juvenile survivorship within their host

aphid, and so the estimated impacts are likely to be conservative.

From Table 2, the effect of these same pesticides on the PGR of other natural enemy species can

be seen. These effects have been divided into three groups causing a 75% or more reduction in

PGR (red), a 25-75% reduction in PGR (yellow) and less than 25% reduction in PGR (green –

see enhancedbiocontrol.org for color rendition). The most consistent impacts with more than a

75% reduction in the PGR of several natural enemy species have been generated by Delegate and

Warrior. For both Cyazypyr and Kumulus, such effects are restricted to particular natural enemy

species, and for the other pesticides tested none show such strong effects. As these results have

been estimated from simple ‘worst case scenario’ bioassays conducted in the laboratory, the

applicability of such results to the field will rightly be questioned. However, evidence from the

long running pesticide-natural enemy testing program of the International Organization for

Biological Control in Europe suggests that laboratory effects of 75% or more on key natural

enemy species are likely to result in real disruption of biological control in the field.

Objective 3. To verify the impact of pesticides identified as disruptive from the laboratory

bioassays through large block replicated field trails in walnut orchards

One of the drawbacks of testing pesticide impacts on natural enemies in the field is that

populations of the natural enemies and their hosts can remain low due to environmental

influences such as climate. The unusually cool springs and summers in both 2010 and 2011 are a

case in point, that has hampered our attempts to verify the disruption of biological control in field

trials in walnut orchards.

As in our field trials reported last year, spider mite and predatory mite populations remained well

below 1 per leaflet until September and were too low to be able to detect the impacts of the

pesticide treatments applied to the two sets of replicated field trials conducted in 2011. Walnut

aphid populations also remained low, but in this case the populations were just large enough to

be able to detect significant impacts of the pesticide treatments (Figs. 4). In the first trial of

reciprocal combinations of Altacor and Delegate applied twice each codling moth generation, the

only treatment to result in a significant increase in aphid abundance in August was that in which

Delegate was applied during the A peak of the codling moth flight each generation. This very

small aphid increase suggests some disruption of biological control and was accompanied by a

reduction in parasitism by T. pallidus in the same treatment blocks (Fig. 4a). Perhaps

surprisingly, the grower standard (Warrior/Lorsban) did not result in a similar disruption of


biological control and increase in aphid abundance in August. This is likely due to the use of

Lorsban which causes long-term suppression of the aphid populations themselves and thus

obscures the disruptive effect on T. pallidus. In the second trial, it is notable that in August the

aphid population was lowest in the Altacor treatment and highest in the Voliam Xpress treatment

(Fig. 4b). The Warrior component of Voliam Xpress likely disrupted the biological control by T.

pallidus and had less of a direct impact on the walnut aphid population than the grower standard

(Warrior plus Lorsban) allowing aphid abundance to increase. However, a corresponding drop in

parasitism by T. pallidus was not apparent in this case.

DISCUSSION

As the management of primary pests in walnuts moves away from the traditional broad spectrum

OP insecticides to newer ‘reduced risk’ products, the impacts of these newer products on the

stability of integrated pest management becomes an important concern. Evidence suggests that

the newer ‘reduced risk’ pesicides are not always compatible with the natural enemies that

contribute very effectively to the management of secondary pests, and in some cases can be

equally disruptive as the more traditional OPs. For many of these secondary pests, the

consequences of changing pesticide use can be complex, as there can be differential influences of

these products at the different trophic levels (pest, primary natural enemy, secondary natural

enemy).

From our laboratory bioassays, it is clear that although many of the newer classes of pesticides

are targeted for other pests and diseases, they can also have impacts on natural enemies. The

results from our laboratory bioassays of the impacts of selected pesticides on two key natural

enemies of walnut aphids, T. pallidus and H. convergens, have been further substantiated by

observations on other natural enemy species through the larger regional project. This research has

demonstrated a clear difference in the potential for disruption of the biological control of

secondary pests through use of either Delegate or Warrior versus Altacor as codling moth

materials. These combinations were subsequently chosen for field verification through replicated

field trails in 2010 and 2011. These two years were particularly unusual in having cool and late

springs with respect to the development and activity of insect populations in walnuts, and this

greatly curtailed our ability to demonstrate disruptive effects in the field. Spider mite populations

remains almost non-existent in our field trails in both years, and while walnut aphids remained

remarkably low, small scale disruptive effects from Delegate were evident both years. Similar

disruptive effects of Delegate have also been observed for biological control of woolly apple

aphid in Washington State and of pear psylla in Oregon, which serve to substantiate the small

scale effects seen for walnut aphid in California.

Substantial progress has also been made with other components of the western regional USDA-

SCRI project on enhancing biological control in western orchards for which this walnut project

forms a matching contribution (http://enhancedbiocontrol.org). Of particular relevance for

walnuts in California are data on the timing of flights by key natural enemies in western orchards,

that can be used to inform the need for selectivity of pesticides for use at different times through

the field season, and the development of new tools for monitoring natural enemy activity, that

can be used to help growers and PCAs visualize natural enemy activity of inform them about the


extent of biological control in specific orchards. In general, natural enemy activity have been

nearly impossible to appreciate in orchards, but we now know that herbivore-induced plant

volatiles (HIPVs) can be used in the same way as moth sex pheronones for monitoring purposes.

Results this season from the USDA-SCRI project have demonstrated that the green lacewing

Chrysoperla plorabunda can be readily monitored using a three part lure (AA + PE + MS) and

that the syrphid Eupeodes fumipennis can be tracked with a two-part lure (AA + GER, Fig. 5a)

and are likely to serve as key indicator species for monitoring the activity of natural enemies in

general. Similarly, we have been able to demonstrate that the green lacewing Chrysopa

nigricornis has three distinct flights through the season that conform to a simple degree-day

model (Fig. 5b).

The patterns arising from this work point to important differences between pest management

products in terms of their selectivity with walnut pest management, and to the value added

benefit of collaborative regional USDA projects in helping to inform pest management decisions

for the walnut industry.

Table 1. Commercial name, active ingredient and field rate of products tested in Objectives 1

and 2

Product Class Active ingredient Field rate (100%)

Warrior II Pyrethroid Lambda-cyhalothrin 2.56 fl oz/acre

Altacor Diamide Rynaxypyr 4.5 oz/acre

Cyazypyr Diamide Cyazypyr 20.5 fl oz/acre

Delegate Spinosyn Spinetoram 7 oz/acre

Rimon IGR Novaluron 50 fl oz/acre

Kocide-Manzate Fungicide Kocide 3000 64 oz/acre

Manzate Prostick 28.8 oz/acre

Kumulus Fungicide Sulfur 320 0z/acre


Table 2. Effects of pesticides on natural enemies tested to date. Cell color reflects changes in

natural enemy attribute: green (1) (< 25% reduction), yellow (2) (25–75% reduction), or red (3)

(> 75% reduction); white − test not yet analyzed.

Altacor Cyazypyr Delegate Rimon Warrior Kumulus

Kocide/

Manzate

NE tested effect measured

Aphelinus mali

acute mortality, adult parasitoidpopulation growth rate, r

Trioxys pallidus

acute mortality, aphid hostacute mortality, adult parasitoid

population growth rate, rDeraeocoris brevis

acute mortality, nymphacute mortality, adult

population growth rate, rChrysoperla carnea

acute mortality, larvaacute mortality, adult

population growth rate, rHippodamia convergens

acute mortality, larvaacute mortality, adult

population growth rate, rGalendromus occidentalis

acute mortality, immatureacute mortality, adult

population growth rate, rPelegrina aeneola

acute mortality, immatureacute mortality, adult

population growth rate, rMisumenops lepidus

acute mortality, immature


Fig. 1. Abbott corrected acute mortality of (a) Trioxys pallidus, and (b) larvae and adults of

Hippodamia convergens, to dilute (0.1x) and full field (1x) rates of the selected pesticides, from

acute laboratory bioassays.

(a) T. pallidus

0

20

40

60

80

100

Altacor Cyazypyr Delegate Rimon Warrior Kocide/Manzate

Kumulus

0.1x

1x

Cor

rect

ed %

mor

talit

y

(b) H. convergens larvae H. convergens adults

-20

0

20

40

60

80

100

Co

rre

cte

d %

mo

rta

lity

0.1x

1x


Fig. 2. Sublethal effects of selected pesticides on survivorship and daily fecundity of Trioxys

pallidus for those products or dilutions (0.1x or 1x) that do not cause severe acute mortality.

0

1

2

3

Female survivorship (days)

0

4

8

12

16

20Daily fecundity (eggs/day)

Fig. 3. Projections from a stage structured matrix model that integrates the population effects of

either the acute or sublethal effects of selected pesticides on individuals of Trioxys pallidus. The

projections show the time delay in regrowth of T. pallidus populations from 10 to 1000

individuals.

0

100

200

300

400

500

600

700

800

900

1000

0 10 20 30 40 50

Po

pu

lati

on

siz

e

Time in days

Control

Warrior II

Kumulus

Cyazypyr

Altacor


Fig. 4. Seasonal abundance of walnut aphid and percent parasitism by T. pallidus in a replicated

field trial of (a) combinations of Altacor and Delegate versus grower standard (Warrior/Lorsban)

and a no spray control, and (b) Altacor and Voliam Xpress versus grower standard

(Warrior/Lorsban) applied during first and second generation codling moth in a walnut blocks

near Chico in 2011. Arrows indicate timing of application and asterisks indicate dates with

significant differences between treatments.

(a)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

5/5 5/26 6/16 7/7 7/28 8/18 9/8

Me

an

wa

lnu

t a

ph

ids/

le

afl

et

Date

Control

Altacor/Delegate

Delegate/Altacor

Warrior/Lorsban

0.00

0.25

0.50

0.75

1.00

5/5 5/26 6/16 7/7 7/28 8/18 9/8

Pro

p.

wa

lnu

t a

ph

ids

pa

rasi

tize

d

Date

(b)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

5/5 5/19 6/2 6/16 6/30 7/14 7/28 8/11 8/25 9/8 9/22

Me

an

wa

lnu

t a

ph

ids/ l

ea

fle

t

Date

Warrior/Lorsban

Altacor

Voliam Xpress

0

0.2

0.4

0.6

0.8

1

1.2

5/5 5/19 6/2 6/16 6/30 7/14 7/28 8/11 8/25 9/8 9/22

Pro

po

rtio

n o

f w

aln

ut

ap

hid

s p

ara

sit

ize

d

Date

Warrior/Lorsban

Altacor

Voliam Xpress


Fig. 5. Use of host-induced plant volatiles (a) to monitor indicator species of natural enemies

Chrysoperla plorabunda (Chrysopidae) and Eupeodes fumipennis (Syrphidae) in walnut orchards

in California in 2011, and (b) to develop degree-day models for adult flights of the green

lacewing Chrysopa nigricornis in orchards in California and Washington.

(a)

(b)


selective pesticides and biological control …walnutresearch.ucdavis.edu/2011/2011_231.pdf ·...

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