A warming Arctic: more mosquitoes, fewer caribou?

Global warming will boost the survival rate of mosquitoes in the Arctic, researchers have found. As a result, caribou may suffer more bloodsucking bites. And the bugs aren’t just a minor annoyance. “Insect harassment” could drive the caribou to areas with less food, ultimately compromising their ability to nurture calves.

The effects of climate change on animal survival are complicated. High temperatures can increase some organisms’ growth rate. The faster they grow, the more quickly they pass through the vulnerable juvenile stages, reach adulthood, and reproduce. But warming could also increase their predators’ metabolism and prompt them to eat more prey.

To find out how these competing effects balanced out, the researchers studied the Arctic mosquito in Greenland. The insects hatch in ponds in late spring, then develop into adults in about a month. During that initial growth period, predators called predaceous diving beetles eat many of the young mosquitoes.

The study authors logged the temperature in four ponds in 2011 and 2012. They also counted mosquitoes and beetles in pond samples and set up traps to catch adult mosquitoes as they emerged.

In the lab, the team raised mosquito larvae in chambers set at different temperatures and observed how long the insects took to develop. Similarly, the researchers put beetle larvae in chambers at various temperatures. Then the team placed the beetles in arenas with mosquito larvae and watched how many they ate.

The higher the temperature, the faster the mosquitoes developed, the team found. Larvae held at 11 degrees Celsius matured in three weeks, while those at 19 degrees took only 10 days.

The beetles ate more mosquito larvae in warmer conditions, but not enough to offset the quicker growth. So overall, warming increased the mosquitoes’ survival rate. A 2-degree increase in pond temperature would boost survival by 18 percent, the team estimates.

Arctic mosquitoes feast on the blood of caribou, and herds may be easy targets during calving. The insects could drive caribou to seek relief in more barren areas with fewer mosquitoes. With less food available, fewer calves may be born or survive to adulthood. Roberta Kwok | 17 September 2015

Source: Culler, L.E. et al. 2015. In a warmer Arctic, mosquitoes avoid increased mortality from predators by growing faster. Proceedings of the Royal Society B doi: 10.1098/rspb.2015.1549.

Image © Pim Leijen | Shutterstock