Global warming is particularly noticeable in the polar latitudes of the earth. In the Arctic, average temperatures have risen twice as fast in the last hundred years as in the rest of the world. As a result, the permafrost thaws in many places and ice and snow covers disappear faster in the spring. Lauren Culler from Dartmouth College in Hanover and her colleagues have now investigated the implications of this for a rather annoying Arctic resident: the arctic mosquito Aedes nigripes. It occurs in the tundra areas of Greenland, but also in Scandinavia, North America and Siberia. When ice melts there in late spring, meltwater pools become breeding grounds for these mosquitoes. For three to four weeks, their larvae live in the water, then pupate and hatch between the end of May and mid-June as a full-grown mosquito. How many of them survive their larvae depends, among other things, on their most important predator, the water bug Colymbetes dolabratus. Once hatched, the female mosquitoes now go in search of a blood meal, in order to then be able to lay eggs again.
Too fast for their enemies
In order to find out how climate change is influencing this development, the researchers sampled four pools of meltwater and their surroundings in the early summer of 2011 and 2012 near the Greenland town of Kangerlussuaq. They collected and counted every two to four days mosquito larvae, pupae and adults, as well as water beetles. It showed that the warmer spring temperatures in 2012 had a direct impact on the mosquito population: the adult mosquitoes hatched two weeks earlier than in the colder spring of 2011. Because some of the larvae had already disappeared from the water until the first water beetles were active, The number of mosquitoes that survived their larvae also increased. "About 20 percent of the mosquitoes had already completed their development until the beetles hatched, " the researchers report. This more than offset the higher activity of the beetles in the following weeks.
In additional laboratory experiments and a population model developed from this, the researchers were able to narrow down the effect of the climate on the mosquitoes. As it turned out, there is an almost linear relationship between larval development time and water temperature: "For every one degree Celsius increase, development accelerated ten percent, " Culler and her colleagues report. "This shortens the time the mosquitoes spend in their larvae stage, which is endangered by the water beetles." The population model showed how strongly this had an effect: According to this, a warming of only two degrees could survive 53 percent more mosquitoes than before. The temperatures in the Arctic ponds even rise by five degrees, then hatch even 160 percent more mosquitoes. This means for all warm-blooded inhabitants of the Tundren: The mosquito season not only starts earlier, it is also always more violent.
But this has consequences especially for larger animals such as caribou and reindeer that live in the Arctic tundra. Because they are in the rather barren landscape one of the main blood suppliers for the hungry mosquito. "The increased mosquito incidence, combined with a northward migration of additional bloodsuckers, will have negative consequences for the health and reproduction of the caribou, " predicts Culler. Because if the mosquitoes hatch sooner in the future, then they go just then hunting for a blood meal when the caribou calves are born. "At these times, the caribou are particularly vulnerable, " explains Culler. "Because there are then especially many weak young animals and the herds are less mobile." Instead of moving into areas with fewer mosquitoes, they stay on site and are stung accordingly more frequently. The same applies to the reindeer herds in the north of Scandinavia and Russia, which are an important source of income for the human inhabitants of the tundra. display
- Lauren Culler (Dartmouth College, Hanover) et al., Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098 / rspb.2015.1549