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 × 1012 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 (<45% mortality). Persistence of OBs on leaf surfaces was examined by subjecting leaf samples to laboratory bioassay in second instar S. exigua. The reduction in OB activity over an 8 day period was greater in leaves sampled from the upper crop canopy compared to those from the lower part of the plant but persistence was not improved in the presence of leucophor AP. The plastic greenhouse structure reduced the intensity of incident UV-B (280–315 nm) readings by not, vert, similar90% compared to external readings. Applications of leucophor AP did not adversely affect the growth of sweet pepper plants over a 14-day period. We conclude that SeMNPV should be adopted as a biological insecticide in greenhouses of this region.