The whine of a mosquito looking for a blood meal in order to develop her next batch of eggs is a constant accompaniment to summertime activities in much of the world, and all over the United States – scientists have identified over 3,000 different species of mosquitoes, 150 of which have been found in North America.
Different mosquito species have different habitats and different behaviors – some develop in swamps, others in ephemeral ponds; some are capable of transmitting malaria, some aren’t; and some don’t bite humans at all, preferring to get the blood they need for egg production from frogs, snakes, or birds.
Adult mosquitoes don’t hatch directly from eggs – they emerge in water as larvae, which mature into pupae before developing into the winged adults that ascend in humming hoards during warm summer months. Their ability to survive to adulthood is influenced by the conditions they experience early in life, and these conditions, as reported in a paper published earlier this year by a team of researchers at Rutgers University, include the species of the other mosquito larvae around them.
The team of scientists filled cups of water with varying proportions of two types of mosquito larvae, and found that, at higher temperatures, one type (the Asian bush mosquito, typically found in clear, clean water) did not survive to adulthood unless there was a small number of the other type (the southern house mosquito, well known to thrive in polluted water, and even raw sewage) present in the same cup. Left on their own, or with too many southern house mosquito larvae present, the Asian bush mosquitoes died.
The scientists observed that the cups containing only the Asian bush mosquito larvae grew yellow and cloudy with the presence of a population of flagellates – single-celled organisms with whip-like tails – which they suspect was responsible for killing the larvae. They postulate that, in the cups where both mosquito species were present, the southern house mosquito larvae saved the Asian bush mosquito larvae from the flagellate, perhaps by eating the microorganisms – but they also point out that they were a benevolent presence only in small numbers. If the southern house mosquitoes made up more than 50 percent of the mosquito population, they appeared to out-compete the Asian bush mosquitoes, whose survival plummeted. At least in cups in a lab, the presence of just the right number of one species of mosquito allowed another species of mosquito to survive.
These findings suggest that mosquitoes that are able to survive in polluted habitats may, in some cases, change those habitats to the extent that other species can move in, too; the researchers write, “if mosquitoes are capable of increasing the geographic range . . . of other mosquitoes, this could result in the establishment of new diseases or increased transmission efficiency of existing ones, with devastating impacts on native wildlife and humans alike.”
Mosquito larvae are influenced by the conditions in their immediate surroundings, including the species of their neighbors – and those dynamics have important implications for their eventual fate as adults, buzzing in our ears.