Roundup®, but Not Roundup-Ready® Corn, Increases Mortality of Drosophila melanogaster

Abstract

Genetically modified foods have become pervasive in diets of people living in the US. By far the most common genetically modified foods either tolerate herbicide application (HT) or produce endogenous insecticide (Bt). To determine whether these toxicological effects result from genetic modification per se, or from the increase in herbicide or insecticide residues present on the food, we exposed fruit flies, Drosophila melanogaster, to food containing HT corn that had been sprayed with the glyphosate-based herbicide Roundup®, HT corn that had not been sprayed with Roundup®, or Roundup® in a variety of known glyphosate concentrations and formulations. While neither lifespan nor reproductive behaviors were affected by HT corn, addition of Roundup® increased mortality with an LC50 of 7.1 g/L for males and 11.4 g/L for females after 2 days of exposure. Given the many genetic tools available, Drosophila are an excellent model system for future studies about genetic and biochemical mechanisms of glyphosate toxicity.

Toxicological Effects of Roundup® on Drosophila melanogaster Reproduction

“…Therefore, we chose commercially available formulations to ensure that our results are ecologically relevant. This approach is consistent with many other studies in Drosophila [ 1 , 13 , 19 , 39 ] and other organisms [ 40 , 41 , 42 , 43 , 44 , 45 ]. The treatment vials contained food medium with either 0.0 g/L (organic control medium), 0.5, 1.0, or 2.0 g/L glyphosate acid equivalent.…”

“…The treatment vials contained food medium with either 0.0 g/L (organic control medium), 0.5, 1.0, or 2.0 g/L glyphosate acid equivalent. These concentrations were selected to minimize mortality based on LD 50 as reported in Talyn et al [ 19 ]. For treatments 1–3, 4.2, 8.3, or 16.7 mL of Roundup ® Ready to Use, which contains the active ingredients glyphosate and pelargonic acid, were added to 100 mL of medium to achieve the following final concentrations, respectively: 1.0, 2.0, and 4.0 g/L total (0.5, 1.0 and 2.0 g/L of each active ingredient, respectively).…”

“…While pelargonic acid toxicity is not well-studied, Techer et al [ 18 ] reported that pelargonic acid exposure as low as 0.05 to 5 mg/L in zebrafish ( Danio rerio ) caused increased activity of glutathione peroxydase, an enzyme that protects against oxidative damage, and pelargonic acid exposure decreased circulating sex hormone levels in both male and female D. rerio . Additionally, pelargonic acid exposure increased mortality in the fruit fly, Drosophila melanogaster , both as the only active ingredient and in formulation with glyphosate [ 19 ].…”

“…D. melanogaster have been widely studied and used as a model organism in biomedical research for over a century [ 34 ]. Drosophila , which have a similar diet to humans in that they require a variety of proteins, lipids, and fats, are an advantageous model system because they are easy and inexpensive to maintain in the lab and yield large sample sizes due to their short adult lifespan and high reproductive rate [ 19 ]. Furthermore, Drosophila are useful in the study of human diseases as many disease genes are highly conserved between Drosophila and humans.…”

“…In Drosophila , glyphosate led to a reduction in ROS (reactive oxygen species) levels and an increase in the gene expression of the antioxidant defense system [ 1 , 39 ]. Glyphosate decreases body size and increases mortality in Drosophila [ 1 , 39 ] at concentrations as low as 1 g/L, which is within the environmentally relevant range [ 19 ]. As with other species, glyphosate showed reproductive effects in Drosophila , specifically a nearly complete decrease in the presence of larvae in the vials of Drosophila exposed to glyphosate at concentrations above 1 g/L [ 19 ].…”