A hybrid insecticide-resistant "super mosquito" capable of carrying malaria has been discovered in Mali in west Africa, the result of interbreeding between two existing species, researchers say.
The new mosquito has proven itself to be resistant to bed nets treated with malarial insecticide, and is likely the evolutionary result of the introduction and use of the nets in its environment, they say.
While the treated nets have helped bring down the number of malaria deaths over the past 10 years, experts say they're not surprised by the emergence of a new insecticide-resistant species.
"Growing resistance has been observed for some time," says lead researcher and medical entomologist Gregory Lanzaro from the University of California, Davis. "Recently it has reached a level at some localities in Africa where it is resulting in the failure of the nets to provide meaningful control, and it is my opinion that this will increase."
The study findings are strong evidence that man-made changes -- such as an introduction and use of the treated nets -- can alter evolution, in the present case breaking down the "reproductive isolation" between the two malaria-carrying mosquito species that are now interbreeding, he says.
The new hybrid species is the result of a kind of gene-swapping known as "adaptive introgression" that occurred concurrently with the increased usage of insecticide-treated bed nets, the researchers say.
"What we provide in this new paper is an example of one unusual mechanism that has promoted the rapid evolution of insecticide resistance in one of the major malaria mosquito species," Lanzaro says.
The study revealed that a significant malaria vector species of mosquito, Anopheles gambiae, is interbreeding with another but less widespread variety, Anopholes coluzzi, resulting in a separate, new species.
With the feared but not unexpected emergence of insecticide resistance, there's "an urgent need to develop new and effective malaria vector control strategies," says Lanzaro.
Malaria is caused by a parasite known as Plasmodium that can enter the bloodstream when a human is bitten by a parasite-infected mosquito.
The parasite can multiply inside the liver and subsequently infect red blood cells, disrupting blood supply to a person's vital organs and potentially causing death if not treated.
Among new control strategies being pursued are improved insecticides, biological agents such as mosquito-killing fungi and bacteria, and genetic management of mosquito species intended to either kill them or alter a species' ability to carry or transmit the Plasmodium malaria parasite.