Earlier spring melt usually means earlier emergence of Arctic mosquitoes, as foes of the biting insects know well.
Now a study from Dartmouth College that combined field observations in Greenland with controlled experiments has quantified the expected rate at which mosquitoes development will accelerate as Arctic temperatures increase.
For every 1-degree Celsius increase in temperature, the Greenlandic mosquitoes need 10 percent less time to emerge as adults, concluded the study in the Proceedings of the Royal Society B: Biological Sciences.
Faster development into adults means greater probability of survival through the larval stage, and the study found that a temperature increase of 2 degrees Celsius increased survival probability by 53 percent. A 5-degree Celsius increase in temperature boosted survival probability by 160 percent, according to the study.
Earlier melt helped the Greenlandic mosquitoes thrive, even though it also brings more predation from a local beetle that eats mosquito larvae, among other things. Those beetles hatch out early as well, meaning that early maturation of mosquitoes is good for them, said lead author Lauren Culler, an Arctic postdoctoral fellow at Dartmouth.
"They are hatching out right in time to have extremely abundant food," she said.
The increase in predation by beetles, however, is far outweighed by the effects of quicker maturation of mosquitoes, leaving mosquitoes with much higher survival rates in warmer temperatures, she said.
For caribou, which have been declining dramatically in Greenland, faster mosquito development can be bad news. The caribou calving season depends on degree of daylight, not temperature, so it's fixed at a certain time of the year -- the beginning of June in the study area of Greenland. That means if mosquitoes emerge as adults at the same time, newborn calves and less-mobile adult caribou will be subjected to bigger clouds of biting insects, Culler said.
"If the mosquitoes are coming out right around that time, it's when the herd is the most vulnerable," she said.
With the Arctic warming at about twice the rate of the rest of the world, faster emergence of mosquitoes is likely to be the trend into the future, though there will be year-to-year variability, Culler said.
Field work for the study was done in the summers of 2011 and 2012 in western Greenland, between the town of Kangerlussuaq and the edge of the Greenlandic ice sheet. Those two Greenlandic summers -- one cold and one warm -- provided illustrative material, Culler said.
The ponds where she and her colleagues worked melted two weeks earlier in 2012 than in 2011, and the average mosquito hatch dates were similarly affected -- June 1 in 2012, versus June 15 in 2011, according to the study.
The quick emergence of adult mosquitoes in 2012 was obvious to locals in Kangerlussauq, Culler said.
"It's a very short time that the mosquitoes are out, and it's the talk of the town when the mosquitoes are out early," she said.
Those mosquitoes live for only about six weeks, Culler said. So there could come a time when, if there is sufficient warming, mosquitoes would emerge as adults well before the caribou calving season, she said.
"It's not all like a gloom and doom story for the caribou and a positive story for the mosquitoes," she said.
The study is one of the few that has examined Arctic mosquitoes and their ecological role in a changing climate, Culler said. Most mosquito research has focused on the tropics, where the insects carry deadly diseases.
Additional Arctic mosquito research has been underway in Alaska at the Toolik Field Station, the Arctic research camp operated by the Institute of Arctic Biology at the University of Alaska Fairbanks. There, Ashley Asmus, a graduate research assistant at the University of Texas at Arlington, has been studying diversity of insect populations, including mosquitoes.