Testing candidate biological control agents for bagrada bug, Bagrada hilaris

Bagrada bug, Bagrada hilaris Burmeister (Hemiptera: Pentatomidae), is a damaging invasive pest of cole crops in California. The host specificity and foraging abilities of two candidate biological control agents for B. hilaris, the egg parasitoids Gryon gonikopalense and Trissolcus hyalinipennis (both Scelionidae), are currently being investigated in quarantine. Unlike most stink bugs, B. hilaris bury their eggs individually in the soil rather than laying egg masses on host plants, and a biological control agent is needed that can locate and attack eggs under the soil surface. Results show that G. gonikopalense is more host specific than T. hyalinipennis, and is able to locate and parasitize buried eggs, while T. hyalinipennis either cannot or is able to do so at very low levels of efficiency. Subsequent testing revealed that G. gonikopalense is able to parasitize eggs in field-collected soil, although parasitism rates varied between soils from different sites, with higher parasitism rates achieved in coarse soil. G. gonikopalense also 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. Taken together, these results indicate that G. gonikopalense is a promising biological control agent for B. hilaris.