Direct and Indirect Effects of a Glyphosate-Based Herbicide on Spodoptera frugiperda Multiple Nucleopolyhedrovirus (Baculoviridae) on Diet, Maize Plants and Soil

Glyphosate is a broad-spectrum, systemic herbicide that has attracted concern over its non-target effects, environmental persistence, and the presence of residues in food. The fall armyworm, <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae), is a major invasive pest of maize that can be controlled by application of its homologous nucleopolyhedrovirus (SfMNPV), an occluded virus in the family <i>Baculoviridae</i>. We examined the effects of a glyphosate-based herbicide on <i>S. frugiperda</i> growth and survival and on virus occlusion bodies (OBs) exposed to product label-recommended concentrations of the herbicide. Larval growth, time to pupation, pupal weight, duration of the pupal stage and sex ratio were not affected by exposure to the herbicide (1% <i>v</i>/<i>v</i> solution) applied to the surface of semi-synthetic diet. Exposure to 1-2% herbicide solution had no effect on the median lethal concentration (LC₅₀) of OBs, the susceptibility of second instar larvae to virus infection, or the production of OBs in virus-killed larvae. Virus acquisition did not vary significantly when larvae fed on virus-sprayed maize plants at 1 and 6 days after they had been treated with herbicide, compared to healthy plants. Finally, the presence of 2% herbicide solution did not influence the persistence of OBs in non-sterilized soil samples over a 6-week greenhouse experiment. Although the laboratory and greenhouse experiments indicated that the glyphosate-based herbicide tested was unlikely to influence the transmission or persistence of SfMNPV OBs, future studies should verify these findings across a range of field conditions, soil types and different herbicide formulations.