Two genes located in the insulin signalling pathway of mosquitoes helps them survive the acute cold in winter, researchers have revealed.
They study led by David Denlinger, senior author and professor of entomology at Ohio State University examined Culex pipiens, a common mosquito in the United States and the species that carries the West Nile virus in North America.
The shorter days of autumn trigger certain species of mosquitoes into diapause, a hibernation-like state of arrested development that allows them to survive through the winter.
Denlinger said that the study has shown that a hormonal response is behind the mosquito's ability to store up extra fat and halt reproductive activity in preparation for its months-long dormancy.
The team identified several genes in this mosquito that function within the insulin signalling pathway, the mechanism necessary to trigger diapause.
However, they focused on two genes that appear to have the most power in regulating the insect's transition into a dormant state.
The two genes were insulin receptor that binds to insulin to initiate its action, and a gene known as FOXO, or forkhead transcription factor, which is typically suppressed in the presence of insulin.
"This winter survival is an absolutely critical phase. Most insects cannot survive through the winter unless they go into a dormant state," said Denlinger.
"Right now, we're focused on the mechanism at the physiological and molecular level. But it does have that kind of potential for application in the future," he added.
In this species, only females survive the winter. Males and females mate before the onset of winter. Females refuse to take a blood meal, and instead feed only on sugar. Their ovaries stop working, so their eggs will not mature. And they accumulate plenty of fat to sustain them over the winter.
Denlinger's lab is examining these species of mosquito in two different artificial day-length environments to either impose a dormancy cycle or to prevent their shift to diapause. Some are reared under short-day conditions, with 12 hours of light and 12 hours of darkness, and others are reared with long days 15 hours of light and nine hours of darkness.
When the mosquitoes living under long daylight conditions were prepared to deposit mature eggs, the scientists disrupt the insulin receptor gene from completing its function that halted reproductive activity and forced them to enter a state resembling diapause.
For further analysis the scientists disrupted FOXO gene function in mosquitoes already in a dormant state. Within four days, these mosquitoes stopped retaining accumulated fat, killing more than 80 percent of them within three weeks
"These are very different organisms with a very different evolutionary history - yet they're using this common pathway of insulin signaling to regulate their dormancy.
So an important aspect of this is the suggestion that this might be a common pathway used by lots of organisms to regulate their dormancy period," Denlinger said.
The research appears online this week in the Proceedings of the National Academy of Sciences.