Laboratory Evaluation of Commercial Trichogrammatid Products for Potential Use againstPlutella xylostella(L.) (Lepidoptera: Plutellidae)

In laboratory experiments we compared the mortality ofPlutella xylostellaL. eggs induced by six products of trichogrammatid egg parasitoids. Five of the species were commercially available, and the sixth is under development. Each of the six products represented a single species of trichogrammatid (Trichogrammatoidea bactraeNagaraja,Trichogramma pretiosumRiley,T. ostriniaePan & Chen,T. platneriNagarkatti,T. minutumRiley, orT. brassicaeBezd.), concomitantly with any characteristics inherent with the commercialized culturing of the species (e.g., sex ratio and host upon which they were reared). Host mortality was assessed as the sum of percent parasitism and other direct induced mortality (e.g., host feeding). Three products (T. bactrae, T. pretiosum,andT. minutum) caused the highest mortalities (95 to 98%) ofP. xylostellaeggs, indicating that the focus of further greenhouse and field studies should be on these products. Inconsistent responses between shipments were observed within most of the products, indicating potential problems with quality control. Two products,T. bactraeandT. pretiosum,demonstrated the highest rates of mortality caused by parasitism ofP. xylostellaeggs (69 to 72%). Mortality caused by factors other than parasitism was high in two of the products. Two products,T. minutumandT. platneri,demonstrated the highest levels of nonparasitic mortalities (60 to 63%, or nearly two-thirds of the total mortality by each of these products). Important considerations for evaluating host mortality are discussed.