SciDev.Net

Scientists laced just a few adult resting sites in a cemetery — and killed almost all the larvae in the area

Gregor J. Devine

[SANTIAGO] Scientists have developed a novel method for killing juvenile dengue-carrying mosquitoes — get adult mosquitoes to do it for them.

Researchers working in the Peruvian Amazon used adult Aedes aegypti mosquitoes to carry an insecticide to their own breeding sites, thus killing most larvae found there.

The aquatic habitats, where A. aegypti lay their eggs and larvae develop, are ideal targets for mosquito control but repeatedly treating numerous breeding sites is difficult.

During their life cycle adult mosquitoes must travel between breeding grounds and resting places. Researchers exploited this trait by disseminating a safe and persistent insecticide called pyriproxyfen in the areas where adult mosquitoes rest. The insecticide is neither lethal nor repellent to adults.

The adults then take the insecticide to breeding grounds. This strategy ensures a strong, wide coverage of aquatic breeding sites by treating only a small portion of the adult resting areas because adult mosquitoes move around so much.

The method is particularly suited to the control of mosquitoes that develop in small, protected aquatic habitats in urban areas, say the researchers.

Three field trials carried out in two sites in a public cemetery in Iquitos, Peru, showed that placing insecticide in just 3–5 per cent of the adult resting areas achieved almost total coverage of the aquatic breeding sites. The effect was lethal: between 95–100 per cent of the larvae developing there died compared with an average mortality of 7–8 per cent in uncontaminated sites.

Pyriproxyfen also sterilises adult female mosquitoes and decreases male sperm production. And the tiny quantities required mean its environmental impact is minimal.

"In Iquitos, health department personnel would need to inspect and treat houses every week. If we could put out resting traps with pyriproxyfen theoretically we would not need to treat all containers and houses so frequently," Amy Morrison, one of the researchers and director of the Iquitos Laboratory of the United States Navy, told SciDev.Net.

The technique could also be useful for the control of other disease-transmitting mosquitoes.

"Any species that has predictable resting or feeding sites and breeds in relatively small aquatic habitats would be a potential target," says Gregor Devine, a researcher in the Plant and Invertebrate Ecology Division at Rothamsted Research in the United Kingdom.