Efficacy of optical brightener formulations of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) as a biological insecticide in greenhouses in southern Spain

The efficacy of optical brightener formulations of a native Spanish isolate of Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) was determined for control of S. exigua on greenhouse grown sweet pepper ( Capsicum annuum) in Almeria, Spain. In laboratory bioassays involving diet surface contamination, the 50% lethal concentration in fourth instars was reduced 25-fold and 5731-fold, compared to SeMNPV occlusion bodies (OBs) alone, or in mixtures with 0.1% and 1% of the stilbene-derived optical brightener leucophor AP, respectively. The efficacy of spray applications of 1 × 10 12 OBs/Ha SeMNPV alone, or in mixtures with 0.1% leucophor AP, was tested in a greenhouse planted with sweet pepper. The prevalence of virus infection in larvae collected at intervals post-application and reared on artificial diet in the laboratory was very high (62–97% mortality). Compared to the treatment involving SeMNPV OBs alone, OBs applied in mixtures with leucophor AP resulted in a significant increase in the prevalence of infection in larvae collected at 2 days post-application, but not in insects collected subsequently. In contrast, a chemical insecticide treatment, lufenuron, performed poorly (