MercoPress. South Atlantic News Agency

Mutation of dengue mosquito resistant to pesticides

The peak activity of Aedes aegypti females is in February and March. Spraying poison outside that period only favors genetic resistance to the chemicals

Argentina's National Council for Scientific and Technical Research (Conicet) has identified in the Buenos Aires Metropolitan Area (AMBA) and in the country's northwestern provinces genetic mutations in the Aedes aegypti mosquito (carrier of the dengue virus) that turned them resistant to normally lethal doses of pesticides, the national news agency Telam reported amid a dengue outbreak, which has resulted in 129,150 cases and 65 deaths over the past 12 months.

A study from Conicet La Plata published in the journal Parasites & Vectors focused on AMBA as well as on Tartagal (Salta) and the Calilegua National Park (Jujuy), where mosquitoes of this species can be found.

“There are three genotypes or genetic varieties” of the Aedes aegypti mosquito, explained Conicet researcher Sheila Ons, lead author of the study. “The sensitive, individuals that are hit by the effect of the insecticide and die by flipping; the R1, which has a mutation that makes them resistant but at a low level, and the R2, which has two mutations and is associated with high resistance,” she added.

“In the urban settlements of Greater Buenos Aires, we find populations of R1, which in many municipalities even outnumber the susceptible ones. The situation in the northwest is more complicated: there we detected groups of R2,” the expert pointed out.

“The more insecticides are used, the more the resistant genotype is evolutionarily selected and little by little only the individuals with this genetic advantage are left, which in turn have offspring with a higher proportion of resistance,” she went on.

“It was to be expected that the situation in Brazil would have a correlation here,” Ons added. Brazil has an “extensive and well-studied presence of populations of the insect that are highly resistant to the most widely used chemical products,” the specialist elaborated.

Conicet researcher María Victoria Micieli, another author of the study, said that “we always have to be looking at what is happening in neighboring countries in northern South America because dengue is a regional problem.”

“It all starts with a person traveling and contracting dengue. When he comes back, he is bitten by another mosquito that at that moment becomes infected and continues biting while inside him the virus completes a 14-day cycle, so it is an exponential dynamic, which increases over time. The only way to block this process is to kill the infected mosquitoes,” she said.

Micieli stressed that “once resistance is found ... it is necessary to rethink the campaigns and analyze the possibility of alternating chemical insecticides with biological methods, bait-traps, among others.”

“Fumigation is not always a solution, nor is it done at any time of the day or season. In many squares, parks, and closed neighborhoods, spraying is done throughout the year or before the summer in a 'preventive' way, but that doesn't work. Here, the peak activity of Aedes aegypti females is in February and March, and spraying poison outside that period only favors genetic resistance to the chemicals,” she also noted.