A lot of communication in the animal world occurs via volatile, information-carrying "scent" chemicals, many of which remain to be chemically identified. Generally speaking, pheromones are a type of infochemical used within a species to influence social behaviors and attract mates whereas kairomones send signals between different species and are often used to detect predators and prey. Scientists have now identified two kairomones produced by a common mosquito predator, which effectively repel mosquitoes. The findings may hold the key to developing new, environmentally friendly insect repellents.

When female mosquitoes are ready to reproduce, they seek out suitable water in which to deposit their eggs. Previous studies have shown that if the mosquitoes chemically detect the presence of their water-borne predator, known as a backswimmer (Notonecta maculata), they are less likely to lay eggs in that location. The identity of the chemical cues released by the backswimmers has not been determined, however.

Leon Blaustein, professor of ecology at the University of Haifa in Israel and his colleagues collected air samples above a pool of backswimmers and identified some of the volatile chemicals present. The team then tested the ability of two of the identified chemicals, alone or in combination, to deter egg-laying Culiseta longiareolata mosquitoes from outdoor pools of water in experimental plastic tubs. The researchers found that pools containing both chemicals were most effective, reducing the number of mosquito eggs by half as compared with control pools containing only water. The chemical combo was nearly as effective in deterring mosquitoes as pools containing adult backswimmers. The findings were published online July 2 in Ecology Letters.

The authors acknowledge that while the kairomones may reduce the mosquitoes' immediate risk of predation by backswimmers, they increase the possibility that the females will die by other causes in their search for new water to lay eggs in. "That's why we think these chemicals could be a useful part of a strategy to control the population size of mosquitoes," Rockefeller University professor and co-author Joel Cohen said in a prepared statement. "These newly identified compounds, and others that remain to be discovered, might be effective in controlling populations of disease-carrying insects. It's far too soon to say, but there's the possibility of an advance in the battle against infections disease."

Image of a mosquito courtesy of the U.S. National Parks Service.