Roundup, but Not Glyphosate Alone, Decreases Activity in Drosophila melanogaster via a Neuromuscular Defect

Glyphosate-based herbicides (GBHs) kill weeds and leaves around produce. GBHs elicit great concern because food residues and other exposures may affect human and environmental health. This study examines whether Roundup Super Concentrate (RSC), a GBH, affects activity levels, using Drosophila melanogaster (fruit flies) as a model system. Flies were exposed to RSC, glyphosate (gly), or polyethoxylated tallow amine (POEA), individually or in combination, at multiple ages and concentrations. Using a Drosophila Activity Monitor, we recorded activity levels from exposed and unexposed flies. Exposure to glyphosate and POEA, alone or in combination, did not affect their activity, indicating that other ingredients in the formulation are responsible for this effect. In addition, we examined several mechanisms of action. Flies were exposed to RSC treatments for two days before being released to the control medium to assess whether the effects of exposure were permanent or whether their activity levels could recover. Exposed flies exhibited less activity, especially females and especially at higher concentrations, while released flies only partially recovered. To examine metabolic mechanisms, we looked at whether RSC affected the protein content of individual Drosophila as a proxy for the overall nutritional condition but found no correlation. Neuromuscular defects were assessed using a negative geotaxis assay, which resulted in a correlation between activity and climbing. A reduction in activity is important for animal fitness because it impacts the ability to find food, find mates, and avoid predators.