Lanjiao WANG

The mosquito Aedes aegypti is the main vector of Chikungunya, in the absence of effective vaccines and available treatments, vector control remains the main prevention and defence strategy for controlling the disease. However, the problem of resistance to insecticides is becoming more acute, not least because of the increasing frequency of chemical control of intense epidemics of arboviruses around the world. We want to understand the importance of insecticide resistance in the context of the transmission of the Chikungunya virus by mosquitoes. Aedes aegypti.

From the Ile Royale mosquito population, considered to be the least resistant population in French Guiana, 4 lines of mosquitoes IR03, IR05, IR13 and IR 36 presenting different resistance profiles to the insecticide deltamethrin were isolated. Biological and molecular tests were carried out to characterise the resistance mechanisms at the level of their phenotype and genotype. The results show that IR03 has only metabolic resistance, that IR05 has both resistance to kdr and metabolic resistance, and that IR13/36 has low metabolic resistance.

Over 600 females were orally infected with the Chikungunya virus using an artificial gorging system. For each individual, 3 sets of samples (midgut, head and saliva) were collected independently to quantify the virus, in order to define its vectorial competence in terms of three parameters: the rate of infection, the rate of dissemination and the rate of transmission. The results show that there are significant differences in vectorial competence, more specifically in the rate of dissemination from the midgut to the whole body of the mosquito over time, which is lower in the most resistant line.

Then, to study the interactions between the resistance mechanisms and the midgut barrier, the expression levels of certain genes (CYP 6BB2, CYP 6N12, GST2, Trypsin) that are directly or indirectly associated with deltamethrin resistance were measured in midgut 7 days after the infectious blood meal, whether the head was positive or negative. By complementing these expression levels with genotype information kdrThe results show that the overexpression of detoxification enzymes and the existence of the kdr could have a significant effect on the dissemination of the virus in the body of mosquitoes.

Finally, with regard to the cost of resistance, which is one of the important factors in assessing the vectorial capacity of resistant mosquitoes, isofemal lines show up more clearly in terms of population reproduction (oviposition time, fecundity and fertility) than the development of immature stages, including larval development time, dead larvae and pupae, and sex ratio.

In conclusion, all the data obtained provides a better understanding of the existence of interactions between insecticide resistance and vectorial capacity in mosquitoes. Even if more manipulations concerning functional validation or more in-depth research can be triggered on the basis of this work, we already have more information to help adapt or improve the vector control response, in order to establish the best compromise between control efficacy and increasing resistance.