Powdered starch could clean-up mosquito control. Sprinkled on mosquito breeding grounds, it forms a temporary film on the water surface that smothers these blood-sucking pests without affecting other pond life1.

Xanthan gum, a thickening agent usually found in processed foods such as salad dressing, kills pond-dwelling mosquito larvae as effectively as conventional insecticides, say Barry Pittendrigh at Purdue University in Indiana and his team at the US Fish and Wildlife Service's Prime Hook National Wildlife Refuge in Delaware.

This, the first field test of carbohydrate-based mosquito control, will interest those looking for safer, greener ways to rein-in malaria risk. Rising insecticide resistance among mosquitoes, and the toxicity of certain insecticides, particularly DDT, used in some developing countries, is making malaria increasingly difficult to control.

"Any other method that's more environmentally friendly and effective needs to be looked at," says Kabir Cham, a member of the World Health Organization's Roll Back Malaria programme, which works to replace DDT with safer insecticides. Malaria, carried by mosquitoes related to those studied by Pittendrigh's team, kills more than a million people each year.

But developing alternatives to chemicals isn't easy, warns Joe Conlon, technical adviser for the American Mosquito Control Association. Previous research has turned up other natural mosquito killers, such as peppermint and lemon oils; many flopped commercially because the quantities needed were too high or because they killed too many other insects as well.

The same challenges face starch-based mosquito killers. But the researchers argue that starch could act as a floating carrier for conventional insecticides, preventing the chemicals from sinking below the surface of the water, where they are no longer effective but can harm other organisms.