Combined effect of nucleopolyhedrovirus and Microplitis pallidipes for the control of the beet armyworm, Spodoptera exigua.

BACKGROUND: Nucleopolyhedrovirus (SeNPV) and Microplitis pallidipes are important biological control agents of Spodoptera exigua populations. The interactions between these agents and their combined effect on pest control were investigated in the laboratory and in commercial greenhouses. RESULTS: Microplitis pallidipes searched for and deposited eggs in more healthy larvae than virus-infected larvae 3 days after viral infection. Each female parasitoid that developed in a virus-infected host oviposited in a virus-infected host, or emerged from a cocoon carrying virus transmitted to 4.0, 7.6 or 2.4 healthy larvae respectively. Each female parasitoid exposed to a mixture of virus and 10% honey water solution transmitted the virus to 2.2 healthy larvae. In an experiment with cabbage growing in commercial greenhouses, the pest population reduction was greater by M. pallidipes carrying SeNPV (82.3-89.7% reduction) than by parasitoids without virus (59.5-62.4% reduction). CONCLUSIONS: Control of S. exigua was greater with M. pallidipes plus SeNPV than with M. pallidipes alone. Microplitis pallidipes preferred healthy hosts to infected hosts. Parasitoids were able to complete their development in virus-infected hosts before the hosts died from the virus infection. The parasitoid ovipositors contaminated with the virus could carry and transmit SeNPV.