4.5 Pure glyphosate versus glyphosate-based herbicide
We also investigated whether a glyphosate-based herbicide was more
harmful than glyphosate alone. Numerous studies have demonstrated that
glyphosate formulations (glyphosate mixed with surfactants) are more
toxic than pure glyphosate (reviewed in (Nagy et al., 2019)) but our
study did not show any difference. However, the majority of these
studies used Roundup® formulation which is described as the most
cytotoxic herbicide (Mesnage et al., 2014; Nagy et al., 2019). The
surfactants associated to glyphosate vary from one formulation to
another. Here, we used the Sintagro® formulation and our results suggest
that the surfactant included in this formulation (i.e. alkyl
polyglucosid), which is different from that contained in Roundup®
(i.e. polyoxyethyleneamine), had no effect, at the concentrations
used in our study, on mosquito’s life history traits.
Conclusion
Our results show that exposure to field-realistic doses of glyphosate at
larval stages, pure or in formulation, did not affect mosquito larval
survival rate, adult size and female fecundity. One of our two
experimental blocks showed, however, an effect of glyphosate on the
development time and on the probability of female infection byPlasmodium parasite. However the effect on infection prevalence
was lost when the larvae are subjected to a nutritional stress, probably
due to a lower ingestion of glyphosate. Altogether, our study and those
published recently, tend to suggest that mosquito larvae are more
tolerant to glyphosate than many other invertebrate species. It has been
recently shown that adult exposure to glyphosate perturbs the gut
microbiota of honey bees and ultimately their susceptibility to parasite
infection (Motta et al., 2018). It would be therefore relevant to also
investigate the effect of glyphosate exposure at the adult stage in
mosquito vector.