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Research Project: Biological Control of Invasive Arthropod Pests from the Eastern Hemisphere

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Title: Catch me if you can: novel foraging behavior of an egg parasitoid, Gryon gonikopalense (Hym. Scelionidae), against the stinkbug pest, Bagrada hilaris (Hem. Pentatomidae)

item MARTEL, GUILLAUME - European Biological Control Laboratory (EBCL)
item SFORZA, RENE - European Biological Control Laboratory (EBCL)

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2020
Publication Date: 1/15/2021
Citation: Martel, G., Sforza, R. 2021. Catch me if you can: novel foraging behavior of an egg parasitoid, Gryon gonikopalense (Hym. Scelionidae), against the stinkbug pest, Bagrada hilaris (Hem. Pentatomidae). Journal of Pest Science.

Interpretive Summary: Bagrada bug or painted bug is a major pest of cole crops in its native range of eastern and southern Africa and the Indian subcontinent. In 2008, it was first reported in California, where it now attacks a wide range of Brassicaceae crops, including cabbage, broccoli, and radish. The bug has spread to New Mexico, Mexico, Hawaii, and Chile. Yield losses reached 25% in Arizona on crucifer crops and up to 70% on Indian mustard crops.To date, no efficient monitoring tools exist to long-term manage Bagrada bug populations in North America. The massive economic loss and the lack of alternative control practices led U.S. growers to use broad-spectrum insecticides to reduce local pest populations. As new insecticides have been shown to be less effective on crucifer crops, a program on classical biological control based on foreign exploration in the native range was initiated in 2015. Several parasitoid wasps of Bagrada were collected in Pakistan are now under investigation at USDA ARS European Biological Control Laboratory.The aim of this study was to investigate the behavior of a biocontrol candidate, an egg parasitoid named Gryon gonilopalense.The foraging ability of this egg parasitoid toward the major crucifer pest Bagrada hilaris is investigated for the first time.The parasitoid succeeded in parasitizing buried bagrada eggs, with a maximum success after 72 hours. Success must be based on chemical detection. With this novel and adapted foraging behavior, G. gonikopalense is a promising candidate for the biocontrol of bagrada in the USA, like California, and beyond.

Technical Abstract: Host detection and parasitism by egg parasitoids reflect a strong specificity for host and are issues that only coevolved parasitoids can overcome. Within the context of importation biological control, understanding this specificity will help in making decisions for biocontrol agent selection. The stinkbug pest, Bagrada hilaris Burmeister (Hemiptera: Pentatomidae), originated from Asia and Africa and became invasive in the Americas where it negatively impacts cruciferous cropping systems. A potential biocontrol candidate is Gryon gonikopalense Sharma (Hymenoptera: Scelionidae), a Pakistani egg parasitoid routinely reared. Within Pentatomidae, bagrada possesses a unique behavioral trait, as its eggs are laid belowground. Our study aimed to evaluate the capacity of G. gonikopalense to respond to bagrada ovipositional behavior. Supported by video recordings, we showed that G. gonikopalense exhibits a well-adapted foraging behavior by tracing and successfully parasitizing 2mm-deep buried eggs of bagrada. Four conditions of egg detectability as well as the effect of food availability on foraging success were tested. After 2hours, 71% of tested parasitoids succeeded and 100% was reached after 72hours. Our data suggested that host egg detection could be based on chemical cues with parasitism success reduced up to 20% when substrate was clean or disturbed. Finally, we showed a strong decrease in parasitism success in presence of a food source, but an opposite effect in presence of buried versus non-buried eggs, suggesting potential trade-offs. Evidently, G. gonikopalense is able to overcome both the chemical and physical barrier constituted by the sand to parasitize the pest, but fitness limitations must be considered.