Lethal and sublethal effects of the naturally derived insecticide spinosad on parasitoids of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Laboratory studies were performed on the lethal and sublethal effects of spinosad on three important species of parasitoids attacking Spodoptera frugiperda (J.E. Smith) in Mexico. Reproduction of the braconid Chelonus insularis (Cresson), on treated egg masses was completely eliminated at 200 parts per million (ppm) and reduced by ∼70% at 20 ppm compared to the controls. Adult C. insularis did not avoid contact with residues on maize (200 ppm), but suffered a 7-day reduction in longevity after contact with residues. Initial toxicity of spinosad applied to a natural host of S. frugiperda was concentration dependent and resulted in 23 to 100% mortality of the eulophid Euplectrus plathypenae Howard at 25 to 200 ppm, respectively. The survival of Eu. plathypenae was initially reduced, especially in males, following contact with field weathered residues on maize (200 ppm). However, survival of both sexes rapidly returned to control values on foliage sampled after rainfall. A similar effect was observed in the mortality response of female Eu. plathypenae exposed to residues on sorghum. The ichneumonid Eiphosoma vitticolle Cresson did not avoid reproduction in S. frugiperda larvae that were externally contaminated with 200 ppm spinosad, although all spinosad-treated hosts died before the parasitoid progeny could develop. We use these results to predict the impact of spinosad applications on the foraging and reproduction of these parasitoids in the field. Such predictions require validation by field studies.