Effects of ivermectin sub lethal doses on the locomotor activity of Anopheles aquasalis

Background: Vector control measures based on available tools have demonstrated not to be feasible for malaria elimination. It has been shown that ivermectin affects several aspects of Anopheles species biology. Anopheles aquasalis plays an important role in malaria transmission in Latin American seacoast. Assessing mosquitos’ locomotor activity allows identifying patterns in daily rhythms, which is controlled by an endogenous circadian clock influenced by external signals such as light and temperature. We assessed ivermectin effects on the locomotor activity of An. aquasalis as well as species’ basal activity. Materials and Methods: Colonized mosquitoes were fed by membrane feeding assays with both blood and blood mixed with low concentrations (LC5, LC15, LC25) of ivermectin. Groups were placed in tubes and assessed by a locomotor activity monitor at 12:12 light/dark cicles. Data regarding mosquitoes activity were analyzed considering average locomotor activity at intervals of 30 minutes. Results: Anopheles aquasalis showed a nocturnal and trimodal activity pattern. Activity peaks occurred at the beginning of both the scotophase and photophase as well as at the middle of the scotophase. Higher means were observed in the beginning of scotophase and photophase for all the groups. For whole period, means were significantly different between control and all drug concentrations. When only the photophase was assessed, LC5 and LC15 were significantly different from control, but not LC25. When scotophase and middle of scotophase were evaluated, LC15 as well as LC25 were statistically different from control, but not LC5. In this analysis, no significant differences were observed at the beginning of the scotophase. In the beginning of photophase, differences were detected only between control and LC5, but not LC15. Conclusions: Ivermectin seems to decrease locomotor activity of Anopheles aquasalis in sub-lethal concentrations. The effect increases with the concentrations and is most evident in the scotophase as well as in the beginning and in the end of this period, although its effects may still be observed in the photophase. This study shows evidence that the effects of ivermectin go far beyond those already presented and affect the mosquitos’ locomotion, directly influencing its vector capacity and therefore malaria transmission.