Nucleopolyhedrovirus infection and/or parasitism by Microplitis pallidipes Szepligeti affect hemocyte apoptosis of Spodoptera exigua (Hübner) larvae.

We determined the effects of parasitism by the endoparasitoid Microplitis pallidipes Szepligeti and/or nucleopolyhedrovirus (NPV) infection on hemocyte apoptosis of Spodoptera exigua (Hübner) larvae. Compared to healthy (control) larvae, larvae that were parasitized, virus-infected, or both all showed a significant increase in hemocyte apoptosis during 48-h observation period. The peaks of hemocyte apoptosis in parasitized, virus-infected and parasitized+infected larvae were at 12, 24 and 48 h after treatment, and were 86.7±1.9, 87.4±3.6 and 76.5±1.6%, respectively. Meanwhile, compared to parasitized larvae, hemocyte apoptosis in jointly parasitized and infected larvae increased by 12.9%, 18.7% and 2.8% at 8, 36 and 48 h respectively, and decreased by 39.0% and 9.1% at 12 and 24h. Compared to virus-infected larvae, hemocyte apoptosis in jointly parasitized and infected larvae increased by 13.4%, 2.4% and 15.3% at 8, 36 and 48 h, respectively, and decreased by 4.0% and 29.9% at 12 and 24h. Our study found that joint and separate parasitism and SeNPV infection induced hemocyte apoptosis of S. exigua larvae. It also revealed that NPV infection promoted host hemocyte apoptosis induced by parasitism at early egg and larval stages of M. pallidipes in host larvae, but inhibited the same effect at late egg stage of M. pallidipes in host larvae, and that parasitism promoted host hemocyte apoptosis induced by NPV infection at early egg and larval stages of M. pallidipes in host larvae, but inhibited the same effect at late egg stage of M. pallidipes in host larvae.