4.3 Glyphosate exposure and larval nutritional stress
Many natural (e.g. competition, predation, temperature) and human-induced stressors (e.g. chemical contaminant) are known to impact negatively mosquito life history traits and immunity (Muturi et al., 2012; Shapiro et al., 2016; Vantaux et al., 2016). In nature, mosquito larvae are exposed to multiple stressors and, while all possible outcomes of stressor combinations (i.e. additive, synergistic or antagonistic) may be expected, the effect of the interaction between stressors are overlook in studies on mosquito-parasite interaction. To our knowledge, this is the first study to evaluate how field realistic dose of glyphosate interacts with larval nutritional stress to alter mosquito life history traits and susceptibility to malaria parasite infection. As expected nutritional stress resulted in longer development time and smaller sized adults (Araújo et al., 2012; Takken et al., 2013; Vantaux et al., 2016). The only interaction we observed between food treatment and glyphosate exposure was on the probability of infection of females. The addition of nutritional stress during larvae development appeared to have alleviated the positive effect of glyphosate on the prevalence of Plasmodium infection. When larvae were exposed to glyphosate, the prevalence of infection was significantly higher when a nutritional stress was applied. The amount of glyphosate ingested by the larvae should increase in proportion to the amount of food ingested. Assuming that glyphosate has an effect on the midgut physiology (Gregorc and Ellis, 2011), if the larvae have less food, they will ingest less glyphosate, which will reduce the effect of this molecule.