Mosquitoes seem to have adapted to the widespread use of bed nets by shifting their "peak period of aggression", a new study reveals.
The widespread use of insecticide-treated nets has been credited with a sharp drop in the number of malarial deaths, especially in sub-Saharan Africa but researchers in two African villages where every household was given a net found that the insects changed their period of "peak aggression" from the middle of the night to the pre-dawn hours.
The study in the West African nation of Benin found that three years after the nets were introduced two-thirds of mosquito bites were taking place outdoors as compared to 45 percent when the French researchers began.
According to researcher Vincent Corbel from the Institute of Research for Development in Montpellier, the finding was "worrying since villagers usually wake up before dawn to work in crops, and as such they are not protected by mosquito nets, the Independent reported.
However, Corbel warned against extrapolating wider conclusions from such a geographically-limited study.
Until now concern over the long-term viability of nets coated in insecticide has centred on mosquitoes developing resistance to the chemicals.