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

## TL;DR

This study found that a glyphosate-based herbicide does not harm the fall armyworm or affect the virus used to control it, suggesting it's safe for biological pest control.

## Contribution

The study demonstrates that glyphosate herbicide does not interfere with the efficacy of a nucleopolyhedrovirus used for pest control in laboratory and greenhouse settings.

## Key findings

- Glyphosate exposure did not affect fall armyworm growth, pupation, or sex ratio.
- Herbicide had no impact on virus infectivity, stability, or soil persistence.
- Virus acquisition from treated plants was not significantly altered by herbicide.

## Abstract

Glyphosate is a widely used herbicide that has attracted concern over its potential effects on a diversity of animals, including aquatic organisms and beneficial insects, its persistence in the environment, and the presence of herbicide residues in human food. The fall armyworm, Spodoptera frugiperda is a major pest of maize in many parts of the world. The larvae of this pest can be controlled by applications of its nucleopolyhedrovirus. In a series of experiments, we observed that the growth, pupation, and sex ratio of the fall armyworm were not affected by exposure to recommended rates of the herbicide. Similarly, the presence of herbicide had no effect on the stability, infectivity or soil persistence of the virus, or the acquisition of infection from virus-sprayed herbicide-treated maize plants. Although these laboratory and greenhouse findings suggest that the glyphosate-based herbicide we tested is unlikely to influence the efficacy of this virus as a biological insecticide, these results should be verified in field studies across a range of soil types and different herbicide formulations.

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, Spodoptera frugiperda (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 Baculoviridae. We examined the effects of a glyphosate-based herbicide on S. frugiperda 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% v/v 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.