How an egg parasitoid responds to an unusual stinkbug oviposition behavior: the case of Gryon gonikopalense Sharma (Hymenoptera: Scelionidae) and Bagrada hilaris(Burmeister) (Hemiptera:Pentatomidae)

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

Submitted to: Entomologia Generalis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2021
Publication Date: 5/18/2022
Citation: Martel, G., Scirpoli, F., Sforza, R. 2022. How an egg parasitoid responds to an unusual stinkbug oviposition behavior: the case of Gryon gonikopalense Sharma (Hymenoptera: Scelionidae) and Bagrada hilaris(Burmeister) (Hemiptera:Pentatomidae). Entomologia Generalis. 42(3)457-470. http://doi.org/10.1127/entomologia/2021/1256.
DOI: https://doi.org/10.1127/entomologia/2021/1256

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 2015. Several parasitoid wasps of Bagrada were collected in Pakistan are now under investigation at USDA-ARS-EBCL. The aim of the present study was to study the behavior of the biocontrol candidate, an egg parasitoid named Gryon gonilopalense in response to the oviposition behaviour of.Bagrada. We assessed the oviposition pattern of bagrada in presence of three host plants (broccoli, white mustard and white rocket) and we showed a strong preference for buried oviposition behavior (92% of eggs). In response, we showed that the egg parasitoid preferred parasitizing buried eggs. 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: As an exception, the phytophagous pest Bagrada hilaris (Hemiptera: Pentatomidae) (= bagrada) buries single eggs in the ground. To tackle its spread, an evaluation of the egg parasitoid Gryon gonikopalense (Hymenoptera: Scelionidae) as a biocontrol agent is ongoing. Its ability to detect and parasitize buried bagrada eggs could be a key factor in the short and long-term down regulation of bagrada populations in invaded countries, especially in the U.S.. However, a deeper understanding of both pest and parasitoid oviposition behaviors is warranted. In an experimental study design, we assessed the oviposition pattern of bagrada in presence of three host plants (broccoli, white mustard and white rocket) and at three density levels (one, five or fifteen copulas). Bagrada showed a strong preference for buried oviposition behavior (92% of eggs) with no effect from the host plant neither the individual density. Eggs oviposited on mustard were mainly present on the top third, including apical meristem, but no distribution pattern was observed on broccoli and white rocket. In addition, G. gonikopalense preferred parasitizing buried eggs, which represented 87 % of all parasitized eggs. Nonetheless, G. gonikopalense was able to attack non-buried eggs, including those located near the apical portion of the plant. Artificially increasing the number of non-buried eggs in the experimental design resulted in a slight change in the parasitism distribution with 70% of buried eggs parasitized. This study quantifies field and laboratory observations of bagrada oviposition preferences and gives value to consider G. gonikopalense as a candidate for a biocontrol program.