OVIPOSITIONAL BEHAVIOR AND HOST DISCRIMINATION IN 3 SCELIONID EGG PARASITOIDS OF STINK BUGS

Ovipositional behavior of the scelionid egg parasitoids Trissolcus bas alis (Wollaston), Psix tunetanus (Mineo & Szabo), and two color forms of Trissolcus utahensis (Ashmead) was observed in laboratory experimen ts that employed a common host, the pentatomid Euschistus conspersus U hler. Brood sex ratios were female biased and less than 0.20; P. tunet anus deposited a precise sequence of male and female offspring compare d to the other species. In host discrimination experiments in which in dividual females were presented with an egg mass partially parasitized by a conspecific female, T. utahensis showed considerable oviposition al restraint toward parasitized eggs. When presented with an egg mass partially parasitized by a female of another species-either T. basalis or P. tunetanus-T. utahensis displayed little discrimination and ovip osited in most of the parasitized eggs that it contacted. When the exp eriment was reversed-T. basalis and P. tunetanus females presented ind ividually with an egg mass partially parasitized by T. utahensis-both species showed little discrimination and oviposited in most of the par asitized eggs that they contacted. For eggs in which multiparasitism i nvolved the combination of T. utahensis and P. tunetanus, the latter e merged from over 70%, regardless of whether it was the first or second ovipositing female. When super- or multiparasitism involved the combi nation of the two T. utahensis color forms or the combination of T. ut ahensis and T. basalis, offspring of the first ovipositing female emer ged from over 70% of the eggs. These results are consistent with the v iew that interspecific host discrimination in parasitoids is less comm on than conspecific host discrimination and provide some support for t he hypothesis that brood sex ratio and competitive ability are inverse ly related in guilds of quasi-gregarious egg parasitoids. Implications for the selection of parasitoid species for classical and augmentativ e biological control are discussed. (C) 1996 academic Press, Inc.