Interaction between endoparasitoid Microplitis mediator (Hymenoptera: Braconidae) and nucleopolyhedrovirus in larvae of Helicoverpa armigera (Lepidoptera: Noctuidae)

Microplitis mediator (Hymenoptera: Braconidae) and Helicoverpa armigera nucleopolyhedrovirus (HearNPV) have been broadly used in field for management of cotton bollworm H. armigera (Lepidoptera: Noctuidae) and they both might share resource in the host larvae when simultaneously applied in the fields. This study explored the interactions between M. mediator and HearNPV in H. armigera through bioassay analysis. The mortality of H. armigera caused by HearNPV inoculation on 2nd instars showed linear relationship with the concentration of the inoculated HearNPV, but the mortality due to HearNPV infection was reduced when HearNPV was inoculated on the third and fourth day post-parasitism by M. mediator. The mortality due to parasitism separately decreased with the increasing of the parasitism host instar. The performance of M. mediator, including survival rate, development duration and the cocoon weight declined with the reduction of interval between the parasitism and HearNPV inoculation. The analysis of co-toxicity factor demonstrated the antagonistic effect between M. mediator and HearNPV on H. armigera larvae when HearNPV was orally inoculated at 4 d post parasitism, however, additive effects were revealed when the intervals between virus infection and parasitism were 1, 2 or 3 days. These results indicated that the application of the HearNPV was unfriendly to the releasing of parasitoid M. mediator and the existence of M. mediator might weaken the virulence of baculovirus. The both HearNPV and M. mediator for management of H. armigera should not be used coincidently.