N-Heneicosane
N-Tricosane
Many animals use chemicals to communicate with each other. Pheromones (most of us are familiar with these class of semi-synthetic compounds-used mainly as insect repellents) which influence social and reproductive behaviors within a particular species, are probably the best known and studied. Kairomones are produced by an individual of one species and received by an individual of a different species, with the receiving species often benefiting at the expense of the donor.
Cohen and his Israeli colleagues focused on the interaction between two insect species found in temporary pools of the Mediterranean and the Middle East: larvae of the mosquito C. longiareolata and its predator, the backswimmer N. maculata. When the arriving female mosquitoes detect a chemical emitted by the backswimmer, they are less likely to lay eggs in that pool.
Cohen and his Israeli colleagues focused on the interaction between two insect species found in temporary pools of the Mediterranean and the Middle East: larvae of the mosquito C. longiareolata and its predator, the backswimmer N. maculata. When the arriving female mosquitoes detect a chemical emitted by the backswimmer, they are less likely to lay eggs in that pool.
To reproduce conditions of temporary pools in the field, the researchers used aged tap water with fish food added as a source of nutrients. Individual backswimmers were then placed in vials containing samples of the temporary pools, and air samples were collected from the headspace within the vials. The researchers used gas chromatography-mass spectrometry to analyze the chemicals emitted by the backswimmers.
Cohen and his colleagues identified two chemicals, hydrocarbons called n-heneicosane and n-tricosane (see structures), which repelled egg-laying by mosquitoes at the concentrations of those compounds found in nature. Together, the two chemicals had an additive effect.
Since the mosquitoes can detect the backswimmer's kairomones from above the water's surface, predator-released kairomones can reduce the mosquito's immediate risk of predation, says Cohen. But they also increase the female mosquito's chance of dying from other causes before she finds a pool safe for her to lay her eggs in.
Researchers conclude that, 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 infectious disease.
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