Host searching behavior of Gryon gonikopalense and Trissolcus hyalinipennis (Hymenoptera: Scelionidae), two potential biological control agents for Bagrada hilaris (Hemiptera: Pentatomidae)

Authors: TOFANGSAZI, NASTARAN - University Of California, Davis; Hogg, Brian; Hougardy, Evelyne; STOKES, KEITH - Former ARS Employee; Pratt, Paul

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2020
Publication Date: 8/17/2020
Citation: Tofangsazi, N., Hogg, B.N., Hougardy, E.H., Stokes, K., Pratt, P.D. 2020. Host searching behavior of Gryon gonikopalense and Trissolcus hyalinipennis (Hymenoptera: Scelionidae), two potential biological control agents for Bagrada hilaris (Hemiptera: Pentatomidae). Biological Control. 151. https://doi.org/10.1016/j.biocontrol.2020.104397.
DOI: https://doi.org/10.1016/j.biocontrol.2020.104397

Interpretive Summary: Bagrada bug is a new invasive pest of cole crops (i.e., cabbage, broccoli, kale) in the US. It is native to southern Asia and was first discovered in the US in 2008. Few control options are available for bagrada bug. Pesticides can be effective but are unavailable to organic growers. Biological control (i.e., using natural enemies from the pest’s native range) could provide a long-term solution for controlling bagrada bug, and two parasitic wasps from Pakistan that attack bagrada bug eggs are being tested as possible biological control agents for bagrada bug in California. Bagrada bug may be particularly difficult to control because it lays its eggs singly in the soil, rather than in clusters on foliage as other stinkbugs do. We tested the abilities of the two parasitic wasps to find and attack bagrada bug eggs in soil. Results showed that one of the parasitic wasps could attack eggs under the soil surface, even when the eggs were placed in the soil by hand, while the other wasp attacked very few eggs in the soil. Subsequent experiments were conducted with the more promising parasitic wasp that attacked eggs in the soil, to test its ability to parasitize bagrada bug eggs in a variety of soils from the field, and to examine whether it prefers to search at ground level or in the foliage. The parasitic wasp attacked higher proportions of eggs in coarse soil that contained high amounts of clay, and parasitized more eggs at ground level, indicating that it prefers to search for eggs on the ground.

Technical Abstract: The bagrada bug, Bagrada hilaris Burmeister (Hemiptera: Pentatomidae), is an invasive pest of cole crops in the United States. Two egg parasitoids, Gryon gonikopalense Sharma and Trissolcus hyalinipennis Rajmohana & Narendran (both Hymenoptera: Scelionidae), are being evaluated as possible biological control agents for B. hilaris. Unlike most stink bugs, B. hilaris females do not lay egg masses on host plants but instead bury their eggs singly in the soil. The host searching abilities of the two parasitoids were investigated by looking at parasitism rates of B. hilaris eggs deposited on and beneath the soil surface. Results show that G. gonikopalense is able to locate and parasitize buried eggs, while T. hyalinipennis cannot or can only at very low levels of efficiency. Subsequent experiments were undertaken with G. gonikopalene to test its ability to attack bagrada bug eggs in field-collected soil, and to examine whether it searches preferentially at ground level. Parasitism rates varied between soils from different sites, with higher parasitism rates achieved in coarse soil, although this result may be confounded by higher B. hilaris egg numbers oviposited in fine soil. G. gonikopalene parasitized eggs at higher rates on the floor of cages than at heights of 8, 16 and 23 cm above the cage floor, suggesting that it preferentially searches at ground level.