No abstract

Chemical control measures targeted at Spodoptera exigua in greenhouse sweet pepper crops in Spain have resulted in pest resistance to virtually all commercially available insecticidal products. A multicapsid nucleopolyhedrovirus (SeMNPV), isolated from diseased S. exigua in Spain, was produced in laboratory reared larvae, tested for insecticidal activity in a laboratory bioassay, and was then applied in eleven commercial greenhouses planted with sweet pepper. Virus occlusion bodies (OBs) were applied on two occasions, at an interval of Â7 days, at a rate of 5)10 8 OBs/L of spray in a volume of Â600 L/ha, depending on crop phenology and greenhouse area. The percentage of plants showing recent ( B48 h old) feeding damage fell dramatically in greenhouses with high infestations of S. exigua ; the same pattern was observed, although less dramatically, in greenhouses with low infestations. Average mortality of larvae collected from treated plants at 4 days after each application, and reared in the laboratory until death, was high (70 Á89%) and was not significantly affected by the degree of crop infestation. In a separate trial, the rate of acquisition of infection was examined in larvae that fed on plants treated with 1)10 8 or 5 )10 8 OBs/L of spray. Of the 27 and 60% of larvae, respectively, that acquired infection in the 48 h period after spraying, about half became infected in the first 6 h post-application, irrespective of application rate. Acquisition of infection proceeded more slowly during the night-time compared to the daytime period, underlining the advantages of early morning applications of the virus. We conclude that the Spanish SeMNPV isolate merits registration as a biological insecticide for use in greenhouse crops in this region.