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.
California Walnut Board 232 Walnut Research Reports 2011
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.
California Walnut Board 233 Walnut Research Reports 2011
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
California Walnut Board 234 Walnut Research Reports 2011
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
California Walnut Board 235 Walnut Research Reports 2011
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
California Walnut Board 236 Walnut Research Reports 2011
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
California Walnut Board 237 Walnut Research Reports 2011
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
California Walnut Board 238 Walnut Research Reports 2011
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
California Walnut Board 239 Walnut Research Reports 2011
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
California Walnut Board 240 Walnut Research Reports 2011
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
California Walnut Board 241 Walnut Research Reports 2011
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
California Walnut Board 242 Walnut Research Reports 2011
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
California Walnut Board 243 Walnut Research Reports 2011
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)
California Walnut Board 244 Walnut Research Reports 2011