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.