Foraging abilities and competitive interactions between two egg parasitoids of bagrada bug in California

Bagrada bug, <i>Bagrada hilaris</i> (Burmeister) (Hemiptera: Pentatomidae), is an invasive pest of cole crops in the United States. Because it also feeds on widespread weeds and persists in natural habitats surrounding crop fields, conventional control strategies are often ineffective at providing long-term control. One egg parasitoid, <i>Gryon aetherium</i> Talamas (Hymenoptera: Scelionidae), is a promising biological control candidate because of its ability to parasitise <i>B. hilaris</i> buried eggs. Recently, adventive populations of <i>G. aetherium</i> were recovered from sentinel eggs in California along with a native egg parasitoid, <i>Ooencyrtus californicus</i> Girault (Hymenoptera: Encyrtidae). A better understanding of these parasitoid species' spatial preference for foraging and their possible competitive interactions will help evaluate their host suppression potential. We compared the foraging abilities of these two parasitoid species for eggs deposited below and above ground. We also investigated the effect of interspecific competition on host suppression and the ability of <i>O. californicus</i> to parasitise eggs previously parasitised by <i>G. aetherium</i>. <i>G. aetherium</i> parasitised naturally and manually buried eggs, whereas <i>O. californicus</i> did not. In another experiment, <i>O. californicus</i> parasitised eggs glued to cards, but not in the presence of sand. Results suggest that <i>G. aetherium</i> may be negatively affected by the presence of <i>O. californicus</i>, and there was a slight but significant reduction in total host mortality when the parasitoids were present together. However, the inability of <i>O. californicus</i> to forage in soil likely limits negative interactions between these two species, and the two parasitoids may ultimately complement each other.