Evaluation of three cold storage methods of Bagrada hilaris (Hemiptera: Pentatomidae) and the effects of host deprivation for an optimized rearing of the biocontrol candidate Gryon gonikopalense (Hymenoptera: Scelionidae)

Authors: MARTEL, GUILLAUME - European Biological Control Laboratory (EBCL); SFORZA, RENE - European Biological Control Laboratory (EBCL)

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2021
Publication Date: 8/27/2021
Citation: Martel, G., Sforza, R. 2021. Evaluation of three cold storage methods of Bagrada hilaris (Hemiptera: Pentatomidae) and the effects of host deprivation for an optimized rearing of the biocontrol candidate Gryon gonikopalense (Hymenoptera: Scelionidae). Biological Control. 163: 104759. https://doi.org/10.1016/j.biocontrol.2021.104759.
DOI: https://doi.org/10.1016/j.biocontrol.2021.104759

Interpretive Summary: Bagrada bug or painted bug is reported as 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 has been initiated in 2016. Several parasitoid wasps of Bagrada were collected in Pakistan are now under investigation at USDA-ARS-EBCL, especially the egg parasitoid G. gonikopalense. The aim of the present study was to study the effect of cold storage methods and the effect of host deprivation on the parasitoid G. gonikopalense in order to optimize its rearing process. We also aimed to support sustainable egg production of laboratory bagrada colonies and to facilitate the rearing of the egg parasitoid .Cold storage of host eggs is mainly recognized as an efficient technique for improving the rearing of biological control agents like egg parasitoids. We showed that bagrada bug eggs stored at 5°C up to one month were optimal for successful parasitism by its egg parasitoid without negative effect on progeny. Taken as a whole, our data helped understanding how to best store bagrada eggs in the laboratory for 1) optimizing the egg use for experiments and G. gonikopalense rearing 2) anticipating a low host production and consequences on G. gonikopalense reproduction and 3) optimizing the quality of sentinel eggs in the field f. With this new technical approach, G. gonikopalense is a promising candidate for the biocontrol of bagrada in the USA, like California, and beyond.

Technical Abstract: The cold storage of host eggs is mainly recognized as an efficient technique for improving the rearing of biological control agents like egg parasitoids. However, similar stockpiling methods can lead to various responses from parasitoids, depending on the species considered. Hence, standardization of storage methods is difficult. The egg parasitoid Gryon gonikopalense Sharma, is an egg parasitoid of Bagrada hilaris (Burmeister), an invasive pest on Brassicaceae crops in the Americas. This parasitoid is currently evaluated as biocontrol agent. In this study, we investigated cold storage methods and the effect of host deprivation on G. gonikopalense in order to optimize its rearing process. Laboratory tests were conducted with bagrada eggs stored under three temperature treatments (-20°C, 5°C, 13°C) and six durations (one week to three months). In addition, we assessed the effect of host deprivation on parasitoid fecundity and progeny development. Bagrada bug eggs stored at 5°C up to one month were optimal for successful parasitism by G. gonikopalense without negative effect on progeny. On the contrary, eggs stored at -20°C and 13°C were much less suitable for a parasitism. In addition, G. gonikopalense did parasitize bagrada eggs after up to 60 days of host deprivation, but the fecundity was reduced. Our data will help 1) to optimize bagrada bug egg production for use in laboratory or field experiments, 2) to improve G. gonikopalense rearing and production in the long term, and 3) to optimize quality of sentinel eggs for field deployment.