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

Abstract

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 individually 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, whileT. hyalinipennis either cannot or is able to do so at very low levels of efficiency. Subsequent experiments were undertaken with G. gonikopalense 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. gonikopalense 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.