Spinosad and nucleopolyhedrovirus mixtures for control of Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize

Abstract

Abstract Spinosad (Dow AgroSciences) is a neurotoxin mixture produced during fermentation of a soil actinomycete that has high activity towards Lepidoptera. Diet surface contamination bioassays were performed with Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) and Spinosad alone and in mixtures. The interaction of SfMPNV + Spinosad mixtures in S. frugiperda larvae was generally independent or slightly antagonistic in nature, although weak synergism was detected in mixtures containing 3 ppm Spinosad + 20 or 70 occlusion bodies/mm 2 diet of SfMNPV. Mean time to death was not a reliable indicator of mortality over time in larvae exposed to SfMNPV–Spinosad mixtures because Spinosad killed larvae quickly whereas virus mortality occurred at a much lower rate. Therefore, threshold tolerance analysis was employed to generate time–response curves that showed two clear phases; an initial response to Spinosad until ∼100 h followed by virus-induced mortality at 120–250 h post-contamination. A field trial was performed to assess the degree of pest control achieved by SfMNPV–Spinosad mixtures applied to maize. Recovery of S. frugiperda larvae was significantly reduced in all treatments compared to recovery from control plots. The mixture of SfMNPV with 3 ppm Spinosad resulted in ca. 90% S. frugiperda control, which was 12.5–32% greater than for plots treated with SfMNPV alone. The impact of low concentrations of Spinosad on non-target arthropods present in the maize crop was evaluated in a field trial. Application of 3 ppm Spinosad had very little effect on the abundance of insect natural enemies present on maize plants, whereas application of the product label recommended rate of 200 ppm Spinosad had effects similar to those observed following application of chlorpyrifos. The use of low concentrations of Spinosad merits further study as a means of controlling lepidopteran pests either alone or in combination with other entomopathogens.