Characterizing Fragmentation of Polystyrene Foam Debris by Isopods Oniscus asellus (Isopoda: Oniscidae) and Trachelipus rathkii (Isopoda: Trachelipodidae).

Microplastics present a novel and potentially unique threat to soil ecosystems, one whose effects may be mediated by soil organisms themselves. We investigated fragmentation of polystyrene (PS) foam into microplastic particles by two isopods, Oniscus asellus L. and Trachelipus rathkii Brandt, in laboratory arena experiments. First, we examined the temporal dynamics of fragmentation across a time span of 96 h. O. asellus produced more fragments than T. rathkii, and neither species significantly fragmented the PS foam until 48 h had passed. Second, we asked whether O. asellus would still fragment PS foam in the presence of an alternate, more natural substrate like wood. Wood did not significantly affect fragmentation rates, in line with the few other studies examining the effect of alternate food on soil invertebrates' propensity to consume and/or fragment plastics. Our results provide additional characterization of PS foam fragmentation by isopods and indicate that laboratory experiments involving soil invertebrates and plastic debris can take place over relatively short timespans of four or fewer days, but do not necessarily need to provide alternate food to prove that plastic consumption would still occur in its presence.

Pneumatic spray delivery-based solid set canopy delivery system for oblique banded leaf roller and codling moth control in a high-density modern apple orchard.

BACKGROUND: Pneumatic spray delivery (PSD)-based solid set canopy delivery systems (SSCDS) have demonstrated comparable spray deposition and reduced off-target drift compared with axial-fan airblast sprayers in high-density apple orchards. An important next step is to quantify whether PSD-based SSCDS can provide effective pest management. This study evaluated the biological efficacy of this fixed spray system variant and compared it with that of an axial-fan airblast sprayer. Partial field trials were conducted in a commercial apple orchard (cv. Jazz) trained in tall spindle architecture. Insecticides were applied at a rate of 935 L ha-1 (100 gallons per acre) for both application systems. Twenty-four hours after spraying, leaves and fruits were collected to prepare the laboratory bioassays enabling evaluation of efficacy against obliquebanded leafroller (OBLR) and codling moth (CM). RESULTS: OBLR mortality for SSCDS, airblast sprayer and untreated control treatments after 24 h of larval exposure was 91%, 98% and 4%, respectively and increased to 98%, 100% and 19% after 48 h. First-instar CM leaf bioassay mortality was 100% for SSCDS and airblast sprayer treatment, and 13% for the untreated control at 24 h post exposure. Larval CM mortality on fruit was 100% for SSCDS and airblast sprayer treatments, and 33% on the untreated control. CONCLUSIONS: Insecticides applied using SSCDS and an airblast sprayer had comparable larval mortality in all three assays, significantly higher than the untreated controls. These results suggest that PSD-based SSCDS may provide a viable alternative to axial-fan airblast sprayers in high-density apple orchards. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Soil Invertebrates Generate Microplastics From Polystyrene Foam Debris.

To fully understand microplastics' impact on soil ecosystems, one must recognize soil organisms as not just passively enduring their negative effects, but potentially contributing to microplastics' formation, distribution, and dynamics in soil. We investigated the ability of four soil invertebrates, the cricket Acheta domesticus L. (Orthoptera: Gryllidae), the isopod Oniscus asellus L. (Isopoda: Oniscidae), larvae of the beetle Zophobas morio Fabricius (Coleoptera: Tenebrionidae), and the snail Cornu aspersum Müller (Stylommatophora: Helicidae) to fragment macroscopic pieces of weathered or pristine polystyrene (PS) foam. We placed invertebrates into arenas with single PS foam pieces for 24 h, then collected and assessed the microplastic content of each invertebrate's fecal material, its cadaver, and the sand substrate of its arena via hydrogen peroxide digestion, filtration, and fluorescent staining. All taxa excreted PS particles, though snails only to a tiny extent. Beetle larvae produced significantly more microplastics than snails, and crickets and isopods fragmented the weathered PS foam pieces more than the pristine pieces, which they left untouched. A follow-up experiment with pristine PS foam assessed the effect of different treatments mimicking exposure to the elements on fragmentation by isopods. PS foam pieces soaked in a soil suspension were significantly more fragmented than untreated pieces or pieces exposed to UV light alone. These findings indicate that soil invertebrates may represent a source of microplastics to the environment in places polluted with PS foam trash, and that the condition of macroplastic debris likely affects its palatability to these organisms.

The Presence and Accessibility of Competitive Resources Affect Trapping Efficiency of Spotted-Wing Drosophila (Diptera: Drosophilidae).

Spotted-wing drosophila (Drosophila suzukii, (Matsumura)) is an invasive vinegar fly that has become a serious threat to soft fruit crops. Monitoring for this pest is typically performed using drowning traps baited with live yeast cultures or fermentation volatile blends. Trapping programs using these compounds provide highly variable results across production systems, geographic regions, and growing seasons. Trap competition with fruit is one hypothesis for this inconsistency. This study evaluated the trapping efficiency of yeast and wine baits in the presence and absence of small quantities of host fruits in two binary-choice laboratory experiments. The first experiment evaluated trap capture in clear 946-ml traps with easily accessible water, apple pomace, blueberry, raspberry, strawberry, cherry, or grape as competitive influences. The second experiment evaluated the same competitors, but they were made less accessible. Recapture of flies in arenas containing competitive fruit was reduced by 64-88% when fruit was 'accessible' and from 0 to 51% when it was 'inaccessible' compared with arenas containing a water competitor. All fruit types provided statistically similar levels of trap interference. In the first experiment, yeast captured more flies compared with wine, whereas in the second experiment, wine captured more flies than yeast. Our results support the hypothesis that the presence of fruit or other reproductive resources will reduce trap captures and that this reduction is likely mediated by the relative accessibility of the fruit versus the trap. Thus, attempts to develop population estimates based on traps should incorporate fruit availability/accessibility.

Composting susceptible fruit wastes reduces Drosophila suzukii (Diptera: Drosophilidae) reproductive habitat.

BACKGROUND: Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) is an invasive, polyphagous vinegar fly pest that is primarily controlled by calendar-based broad-spectrum insecticide programs. Nonchemical management tactics are urgently needed to reestablish IPM within affected berry and cherry cropping systems. Composting is a post-harvest crop sanitation strategy that could potentially be used to manage D. suzukii infestation of fruit wastes. RESULTS: This study found that D. suzukii emergence decreased exponentially with an increasing proportion of chicken manure, with emergence reduced by 95% in compost treatments containing 25% chicken manure. Furthermore, Drosophila melanogaster (Meigen) (Diptera: Drosophilidae) demonstrated a response similar to D. suzukii in the field. CONCLUSION: Integrating this control tactic into existing D. suzukii management programs may help to reduce the need for insecticide applications for D. suzukii as well as provide improved management of other Drosophila spp. in post-harvest systems.

Postharvest Burial of Drosophila suzukii (Diptera: Drosophilidae) Infested Fruit Waste Reduces Adult Emergence.

The arrival of spotted wing Drosophila, Drosophila suzukii (Matsumura), to the United States has caused many berry and cherry growers to replace IPM programs with calendar-based broad-spectrum insecticide programs. Alternative management tactics are urgently needed to mitigate the current dependency on chemical control. Postharvest burial is a cultural crop sanitation strategy that has the potential to reduce D. suzukii reproductive habitat and eliminate infested fruit wastes. This study revealed that D. suzukii rarely pupate on the soil's surface or below 1 cm, but are capable of unburying themselves from depths up to 48 cm. Although zero emergence was not obtained in the field, adult emergence decreased exponentially with deeper burial depths. A burial depth of 24 cm reduced D. suzukii emergence by 97%, although soil texture may influence this optimal burial depth. Soils that had a higher concentration of sand had a negative impact on D. suzukii survival at shallower burial depths. The mechanism behind the reduction in adult emergence from differing burial depths remains unclear as the lipid concentration between emerging D. suzukii was the same regardless of burial depth.

Season Long Pest Management Efficacy and Spray Characteristics of a Solid Set Canopy Delivery System in High Density Apples.

Solid set canopy delivery systems (SSCDS) are a novel foliar agrochemical delivery system designed as an alternative for airblast sprayers in high density fruit production. This study tested the pest management potential, coverage, and chemical deposition of an SSCDS using commercially available microsprinkler components over the course of a growing season. Spray coverage and deposition for a representative airblast sprayer and SSCDS were evaluated using water sensitive paper and tartrazine dye, respectively. Foliar sprays for pest suppression were applied through both systems, and damage assessments were taken at the midpoint and end of the growing season. SSCDS sprays demonstrated similar levels of coverage on the adaxial leaf surface as airblast sprays, but significantly lower coverage on the abaxial surface. However, mean levels of foliar chemical deposition was generally higher in the SSCDS. Evaluations found minimal arthropod and fungal damage in both airblast and SSCDS treated plots compared to untreated trees. The SSCDS was shown to be a viable alternative to the airblast, with inherent advantages such as rapid application time and improved worker safety. Furthermore, higher deposition on SSCDS treated foliage supports the hypothesis that SSCDS provide a higher droplet capture rate in the canopy, with less off-target loss and drift than airblast sprayers.

Multistate Comparison of Attractants and the Impact of Fruit Development Stage on Trapping Drosophila suzukii (Diptera: Drosophilidae) in Raspberry and Blueberry.

Spotted-wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), is an invasive pest of soft-skinned fruits across the globe. Effective monitoring is necessary to manage this pest, but suitable attractants are still being identified. In this study, we combined lures with fermenting liquid baits to improve D. suzukii trapping specificity and attractiveness. We also measured the efficiency and specificity of baits/lures during different times of the season; the reproductive status of females among baits/lures; and the effects of locations and crop type on these response variables. We developed a metric that combined mating status and fat content to determine differences in types of females attracted. Lures utilizing yeast and sugar-based volatiles trapped the most D. suzukii. The addition of a commercial lure to yeast and sugar-based lures increased catches in most locations, but was also the least specific to D. suzukii. Apple juice-based chemical lures tended to be most specific to D. suzukii, while lures comprised of a singular attractant tended to trap more D. suzukii with a higher reproductive potential than combinations of attractants. Trap catch and lure specificity was lower during fruit development than fruit ripening. While catch amounts varied by geographic location and crop type, attractants performed similarly relative to each other in each location and crop. Based on the metrics in this study, the yeast and sugar-based attractants were the most effective lures. However, further work is needed to improve early season monitoring, elucidate the effects of physiological status on bait attraction, and understand how abiotic factors influence bait attraction.

Susceptibility of wounded and intact black soldier fly Hermetia illucens (L.) (Diptera: Stratiomyidae) to entomopathogenic nematodes.

Production costs and limited regional availability are two key factors limiting the widespread adoption of entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) in biological control programs. We explore the potential of using black soldier fly larvae Hermetia illucens (L.) (Diptera: Stratiomyidae) as an alternative in vivo rearing host to the greater wax moth, Galleria mellonella (L.) (Lepidoptera: Pyralidae). We injured black soldier fly larvae to test the hypothesis that the tough cuticle was preventing the penetration of founding infective juveniles (IJs) into the host and egress of offspring from the cadaver. Injuring the black soldier fly larvae increased the infection rate, the number of nematodes entering a host, and the number of IJs harvested from a cadaver. Black soldier fly larvae, however, provided at most 10-fold less IJs compared to G. mellonella. In olfactometer assays, we assessed nematode behavioral responses to wounded black soldier fly larvae. Steinernema carpocapsae did not move towards the insects. Heterorhabditis bacteriophora was attracted to black soldier fly larvae but not G. mellonella. Heterorhabditis bacteriophora did not show a preference for injured black soldier fly larvae over non-injured larvae. Thus, increased colonization on wounded black soldier fly larvae was likely due to additional entry points rather than an increase in their apparency in the soil solution.

Floral Scent Mimicry and Vector-Pathogen Associations in a Pseudoflower-Inducing Plant Pathogen System.

Several fungal plant pathogens induce 'pseudoflowers' on their hosts to facilitate insect-mediated transmission of gametes and spores. When spores must be transmitted to host flowers to complete the fungal life cycle, we predict that pseudoflowers should evolve traits that mimic flowers and attract the most effective vectors in the flower-visiting community. We quantified insect visitation to flowers, healthy leaves and leaves infected with Monilinia vaccinii-corymbosi (Mvc), the causative agent of mummy berry disease of blueberry. We developed a nested PCR assay for detecting Mvc spores on bees, flies and other potential insect vectors. We also collected volatiles from blueberry flowers, healthy leaves and leaves infected with Mvc, and experimentally manipulated specific pathogen-induced volatiles to assess attractiveness to potential vectors. Bees and flies accounted for the majority of contacts with flowers, leaves infected with Mvc and healthy leaves. Flowers were contacted most often, while there was no difference between bee or fly contacts with healthy and infected leaves. While bees contacted flowers more often than flies, flies contacted infected leaves more often than bees. Bees were more likely to have Mvc spores on their bodies than flies, suggesting that bees may be more effective vectors than flies for transmitting Mvc spores to flowers. Leaves infected with Mvc had volatile profiles distinct from healthy leaves but similar to flowers. Two volatiles produced by flowers and infected leaves, cinnamyl alcohol and cinnamic aldehyde, were attractive to bees, while no volatiles manipulated were attractive to flies or any other insects. These results suggest that Mvc infection of leaves induces mimicry of floral volatiles, and that transmission occurs primarily via bees, which had the highest likelihood of carrying Mvc spores and visited flowers most frequently.

Biology and Seasonality of the Reemergent Pest Rhynchaenus pallicornis (Coleoptera: Curculionidae) and Methods for Monitoring Its Abundance.

Rhynchaenus pallicornis (Say) is a pest of commercially grown apples in the upper Midwest. This historic pest has resurged and caused severe yield loss on farms using certified organic production practices. The life history and potential monitoring methods of R. pallicornis are presented. Seasonal abundance data were collected through beat and visual sampling. A phenological model was developed for R. pallicornis. The minimum developmental threshold of R. pallicornis was determined to be 3.5°C with a required degree-day accumulation of 125°D for first adult emergence. Larval damage was observed on >60% of leaves in unmanaged orchards and affected significantly fewer basal leaf clusters (near the trunk), than medially or apically located clusters. Of 2,900 R. pallicornis larval mines collected over two years at three different sites, 18.0% produced at least one adult parasitoid, but the targeted larval stage is unknown. Measurements of R. pallicornis larval head capsules and the simple frequency method were used to determine three larval instars of R. pallicornis The number of larval instars could also be accurately determined by observing the presence or absence of two sets of thoracic sclerites. Pyramid traps, yellow sticky cards baited with olfactory cues (pear essence, benzaldehyde, and an aggregation of adult R. pallicornis) were evaluated as R. pallicornis monitoring tools. None of the traps or lures tested significantly affected the number of adult R. pallicornis per trap.

Susceptibility of Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae) to Entomopathogenic Nematodes (Rhabditida: Heterorhabditidae and Steinernematidae).

Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae) and entomopathogenic nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) are two soil-dwelling biological control agents used to manage western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and fungus gnats Bradysis spp. (Diptera: Sciaridae) in glasshouses. Growers often use multiple natural enemies to achieve economic control, but knowledge of interactions among natural enemies is lacking. We conducted a laboratory bioassay to test the pathogenicity of four commercially available nematode species-Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhbditidae), Steinernema carpocapsae (Weiser) (Rhabditida: Steinernematidae), S. feltiae (Filipjev), and S. riobrave Cabanillas et al.-to third instar and adult D. coriaria. Third instars were three times more susceptible than the adults to the entomopathogenic nematodes. Mortality for D. coriaria adults and third instars treated with S. feltiae and H. bacteriophora was lower than the mortality for D. coriaria adults and third instars treated with S. carpocapsae and S. riobrave. Neither infective juvenile foraging behavior nor size correlates with D. coriaria mortality. Dalotia coriaria appears to be most likely compatible with applications of S. feltiae and H. bacteriophora.

Impact of Cultivation and Subsequent Burial on Cydia pomonella (Lepidoptera: Tortricidae) and Conotrachelus nenuphar (Coleoptera: Curculionidae).

We assessed the efficacy of cultivation as a potential management strategy for codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), and plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae) in apple orchards. Cocooned codling moth pupae and thinning apples infested with plum curculio larvae were cultivated over in the field. Emergence, percent burial, damage to buried fruit, and depth of burial was recorded. In the laboratory, both insects were buried at variable depths in sand and potting soil and emergence was measured. A greater proportion of plum curculio larvae buried in infested fruit under laboratory conditions survived to adulthood compared with unburied infested fruit, down to 15 cm. No codling moth adults emerged from under 1 cm or more of sand. Buried codling moth larvae experienced drastically reduced survival to adulthood compared with unburied larvae. These results indicate that strip cultivation may negatively impact codling moth diapausing larvae and pupae on the ground, but not likely to negatively impact plum curculio in infested dropped apples.

Effects of reservoir dispenser height on efficacy of mating disruption of codling moth (Lepidoptera: Tortricidae) in apple.

BACKGROUND: The effect of varying the height of reservoir dispensers for mating disruption of codling moth, Cydia pomonella (L.), was investigated. The goal was to improve the effectiveness of C. pomonella mating disruption through improved understanding of adult distribution within the tree canopy and the impact of pheromone dispenser placement on disruption. Two dispensers per tree were placed at 2 m and 4 m and/or one dispenser at each height on the tree at a label rate of 1000 units ha(-1) . Monitoring traps and tethered female moths were deployed in plots at 2 and 4 m heights to assess treatment effects by catches or matings respectively. RESULTS: Fewest male moths were captured with all dispensers placed at 4 m. Female mating was lowest, and with least variation between females tethered at 2 and 4 m, when dispensers were placed simultaneously at 2 and 4 m (28% mated). Mating was 32% with both dispensers at 4 m, 38% with both dispensers at 2 m and 46% in the no disruption control. Mating was highest across treatments when females were tethered at 2 m and dispensers placed at 4 m (40%), and when females were tethered at 4 m with dispensers placed at 2 m (46%). CONCLUSION: Traps at 4 m in trees captured more male moths than traps at 2 m, regardless of disruption dispenser positioning. Female mating was lowest when dispensers were placed simultaneously at 2 and 4 m, suggesting that current recommendations for placement of reservoir dispensers in tree crowns may be suboptimal.

Direct sampling of resting codling moth (Lepidoptera: Tortricidae) adults in apple tree canopies and surrounding habitats.

Field investigations were conducted to determine the resting locations of codling moth (Cydia pomonella [L.]) (Lepidoptera: Tortricidae) males and females in mating disrupted and nondisrupted apple (Malus domestica Borkh.) orchard plots. A custom-made sampling device, consisting of a leaf blower converted into a powerful vacuum, yielded 20-24% success in recovering marked moths, released in the tree canopy in orchards. Four collections each were made between 0900 and 1800 hours and 1800 and 2200 hours in 2005. Ninety-four moths were collected during the 1800-2200 hours samples. In mating disruption plots, 42% of females and 22% of males were found in the top third of the tree canopy (3.0-4.5m), 46% females and 43% males in the middle third (1.5-3.0m), and 12% female and 35% male in the lower third (0-1.5m). In nondisrupted plots 36.4% of females and 40% of males were in the top third of the canopy, 36.4% females and 52% males in the middle third, and 27.2% females and 8% males in the lower third of the tree canopy. Daylight vacuum sampling recovered only one female and two male moths from the top, four males from the middle and one male from the lower third of the tree canopy. Release-recapture studies of marked adult codling moths were conducted in 2006-2007 in screened tents to determine within orchard habitats for adult moths during 0900-1800 hours. Of moths recaptured, 14.6% of females and 13.5% of males were from the ground (herbicide strip and drive-row grass) and 32.9% of females and 24.6% of males were captured in the tree canopy 16-h post release, 17.4% of females and 3.4% of males from the ground and 26.5% of females and 38.2% of males in the tree 40-h post release, and 15.1% of females and 18.6% of males from the ground and 15.7 of females and 25.5% of males in the tree 64-h post release. Application of pyrethrum + PBO by using an orchard blast sprayer in 2007 resulted in the recapture of 28% and 37% of laboratory reared male and female moths, respectively, from trees during 0900-1800 h. Our results suggest that distributing pheromone dispensers throughout the tree canopy may be more effective than placing them in one location, such as near the tree crown.

Effect of pheromone dispenser density on timing and duration of approaches by peachtree borer.

The timing and duration of approaches by male peachtree borer Synanthedon exitiosa Say (Lepidoptera: Sesiidae) to commercial pheromone dispensers placed singly or at high density in peach orchards was determined by using field-deployed video cameras and digital video recorders. Cameras were trained on one dispenser, and one standard lure was placed in a peach orchard, and on 12 dispensers in a separate orchard where dispensers for mating disruption had been placed at 371 per hectare. Male moth approaches were video recorded at the peak of peachtree borer annual flight, from 13 to 18 August 2009. The mean approach timing (h:min:sec±SD) during the study period was 11:33:12 ± 00:46:43, 11:43:52 ± 00:45:58, and 11:41:21 ± 00:45:54 AM with the single dispenser, high-density dispensers, and lure, respectively. Day-to-day variability in approach timings suggested that there were no biologically significant differences among treatments. The frequency distribution of approach durations varied among treatments, as the high-density dispensers had mostly short approaches, while the distribution of approaches to the single dispenser and lure was wider. The median (interquartile range) approach duration was 3 (2-4), 1 (1-2), and 4 (2-6) seconds with the single dispenser, high-density dispensers, and lure, respectively. The relative rank of median approach durations was constant throughout the period, indicating differences among treatments. This study showed that the presence of pheromone dispensers for mating disruption did not cause an advancement of peachtree borer diel rhythm of response. Shorter approaches to dispensers placed at high density than singly suggest that dispenser retentiveness is not constant with peachtree borer, which may bias estimates of disruption activity as a function of dispenser density.

Recapture of codling moth (Lepidoptera: Tortricidae) males: influence of lure type and pheromone background.

Recapture of marked male codling moths, Cydia pomonella (L.) (Lepidoptera: Tortricidae), released four distances from traps was measured in experiments comparing either lure type or mating disruption. Experiment 1 assessed recapture by 0.1, 1, and 10 mg of codlemone lures. Experiments 2 and 3 assessed moth recapture in orchard plots with 0, 500, or 1,000 Isomate C Plus dispensers per ha. Moths were released 1, 3, 10, and 30 m downwind of the trap in experiments 1 and 2, and 3, 10, 30, and 45 m in experiment 3. Lure type did not affect recapture, however, significantly more moths were recaptured at 3 m compared with 10 or 30 m. Most moths recaptured < or = 10 m of the trap were recaptured by day 3, whereas most of the moths recaptured > or = 10 m were recaptured after day 3. Thus, 0.1-, 1-, and 10-mg lures, have an attractive range of between 10 and 30 m in orchards lacking mating disruption. Both mating disruption rates greatly reduced moth recapture, and moths recaptured under a 1,000 dispenser per ha rate were recaptured from < or = 10 m and within the first 2 d after release. Similar results were observed when release points were expanded to 45 m. Thus, results suggest that pheromone dispenser technologies and placement strategies that maximize disruption of males that arise within 10 m of a female are needed to markedly improve mating disruption.

Effects of intra- and interpatch host density on egg parasitism by three species of Trichogramma.

Host-foraging responses to different intra- and interpatch densities were used to assess three Trichogramma spp. (Hymenoptera: Trichogrammatidae) Trichogramma deion Pinto and Oatman, T. ostriniae Pang and Chen, and T. pretiosum Riley - as potential biological control agents for the Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae). Single naïve females were allowed 6 h to forage in Plexiglas arenas with four different spatial arrangements of host eggs, nine single-egg patches), nine four-egg patches, 36 single-egg patches, and 36 four-egg patches. No significant differences were found among species in the number of patches parasitized. As expected, all three species parasitized the most eggs in the 36 four-egg patch treatment and the least in the nine single-egg patch treatment. T. deion parasitized significantly more eggs than T. pretiosum on the nine four-egg patches. T. ostriniae parasitized significantly more patches when intrapatch density was greater, regardless of interpatch density. In contrast, T. deion only parasitized more patches at the greater intrapatch density when the interpatch density was low. Patch density had no effect on T. pretiosum. The spatial pattern of parasitism was more aggregated for T. deion and T. ostriniae in the 36 four-egg patches treatment compared to the 36 single-egg patches treatment. Therefore, intrapatch density was more important than interpatch density for T. ostriniae, and potentially for T. deion, but not for T. pretiosum. T. deion may be the best candidate for augmentative biological control because it parasitized either slightly or significantly more eggs than the other two species in all four treatments. Furthermore, the pattern of parasitism by T. deion in the 36 four-egg patches treatment was the most aggregated among the three species, suggesting a more thorough searching pattern. In contrast, T. pretiosum had the least aggregated pattern of parasitism and therefore may have used a more random foraging pattern.