Mosquitoes on the Thawing Tundra

Mosquitoes may not be the first thing most people associate with Greenland, but as arctic temperatures rise we may start hearing more about these pesky critters. Dr. Lauren Culler uses these mosquitoes and the snow-melt ponds they breed in as a fascinating study system to investigate changes in mosquito life cycles within a rapidly changing environment

When considering arctic animals impacted by climate change, mosquitoes may not be the first that come to mind. However, Dr. Lauren Culler from Dartmouth’s Institute of Arctic Studies presented a clear case for why we may want to pay more attention to these northern pests. Lauren conducts her research in Greenland, where there is a single species of mosquito, Aedes nigripes. They breed in shallow wetlands formed by snowmelt on the tundra. The mosquitoes are well-adapted to their unusual breeding sites, and emerge in vast numbers (Figure 1), voraciously attacking both humans and caribou in their quest for blood meals. Because average winter temperatures in Greenland have increased by 4°C (7.2°F) in the last 40 years, Lauren wanted to investigate the impact that this rise in temperature has on the mosquitoes. And, as a result, what impact a change in the mosquito’s lifecycle might have on the people and caribou they torment. Perhaps expectedly, the answer is quite complicated.

As with most insects, mosquito larvae develop faster in warmer temperatures. Interestingly, Lauren noticed the temporary wetlands contained predaceous diving beetle larvae in addition to the mosquitoes. Lauren raised the question: if the beetle larvae develop faster as well, how might the interaction between the two organisms change in rising temperatures, and what would this do to the mosquito populations? She measured mosquito survival to adulthood at different temperatures. At higher temperatures, mosquitoes experienced higher daily mortality rates due to increased predation pressure. However, they also spent fewer days exposed to predators because of their faster development. Taken together, warming had a net positive effect on mosquito survival to the adult stage.

Figure 1. 1,900 adult mosquitoes collected in 12 hours in one of Lauren’s traps. Photo Credit: Lauren Culler

Figure 2. A mosquito flies above a Greenland pond. Photo Credit: Lauren Culler

Lauren was interested in studying the system from more than just the larval mosquito life stage. As immature mosquitoes survive to adulthood, they look for a blood meal and then for habitats to lay their eggs and continue the cycle (Figure 2). However, blood meals are variable across the landscape and the quality of some wetlands may be better than others. Lauren found that the mosquitoes emerging near to a caribou herd, which provided accessible blood meals for mosquitoes, lay more eggs, but the survival of those eggs into the next generation of adults is determined by the quality and availability of the immature habitat. In a warming Arctic, wetlands may dry up faster, before mosquitoes have completed their development to the adult stage.

The third part of the research Lauren presented uses a long-term dataset to test for the environmental drivers of mosquito emergence (Figure 3) and changes in relative abundances. Analysis of weekly monitoring during growing seasons since the 1990s has shown that mosquitoes are emerging around 4 days earlier per decade. This result led Lauren to think about what environmental factors drive this early emergence. The first factor is the date of first pond melt. Even when ponds melt early the water temperature is still low which could delay the larval development. However, the more important factor is the temperature. The higher temperature will directly affect mosquito development and lead to earlier emergence. To know what was driving relative abundance, Lauren also tested how snow depth, temperature and spring freeze-thaw events impact the relative abundance of mosquitos collected in window traps. The results showed that temperature and spring freeze-thaw events both had negative correlation to abundance while snow depth showed positive correlation to abundance. The temperature showed a negative result, which surprised Lauren because her empirical work suggested that warming would lead to larger mosquito populations. The reason why temperature showed a negative result needs to be studied further.

Lauren’s research studied how environmental changes affect mosquitos’ immature survival, adult reproduction and the population dynamic change in Greenland. The rapid increase in temperature and more days above freezing than before resulted in faster mosquito development and earlier emergence, however, the mechanisms behind these trends are uncertain and need to be investigated in future study. Lauren is also interested in further investigating the caribou aspect of her study system, as they serve a major role in the local economies but experience a lower reproductive rate when harassed by mosquitoes. She hopes her research can help the Greenland residents plan their futures in a rapidly changing climate.

Figure 3. A mosquito emergence trap on a tundra wetland. Photo Credit: Lauren Culler

Becca Wilson is a PhD candidate in the Lamp Lab. She studies the spatial distribution and societal impacts of nuisance black flies in western Maryland.

Mengyao Chen is a PhD student in Dr. Leslie Pick’s Lab. Her research focuses on segmentation genes in Brown Marmorated Stink Bug (BMSB, Halyomorpha halys) and Firebrat (Thermobia domestica)