Virion-free plasma from entomopoxvirus-infected larvae of Pseudaletia separata (Lepidoptera: Noctuidae) kills larvae of a braconid endoparasitoid, Cotesia kariyai (Hymenoptera: Braconidae) cultured in vitro

Virion-free plasma from larvae of the armyworm, Pseudaletia separata, infected with an entomopoxvirus (PsEPV), adversely affects the embryonic and larval stages of the gregarious braconid endoparasitoid, Cotesia kariyai. We investigated the toxicity of virion-free plasma from PsEPV-infected P. separata larvae against C. kariyai embryos and larvae cultured in vitro. Parasitoid larvae collected from host larvae were individually transferred into plastic Petri dishes with IPL-41 medium and culture at 25°C for 7 d. The development of C. kariyai larvae was adversely affected when virion-free plasma was added to IPL-41 medium, even up to a dilution of 128. The mortality of in vitro-cultured parasitoid larvae decreased with increases in the concentration of virion-free plasma added to the medium. The parasitoid larvae became less susceptible to the lethal factor as the larval stage increased. Parasitoid larvae culture in IPL-41 medium added to virion-free plasma developed little if at all, and shrank and died 2 to 6 d after the start of culture, regardless of the larval stage of the parasitoid. In dead parasitoid larvae, the tissue receded from the cuticle and organs lost their organization and cellular integrity. Embryos cultured in IPL-41 medium containing virion-free plasma never progressed beyond the egg stage, and somatic tissues lost their organization. On the other hand, embryos cultured in IPL-41 medium containing normal plasma developed to the first stadium.