Featured Article: Medley, K. A., K.M. Westby, and D.G. Jenkins. 2019. Rapid local adaptation to northern winters in the invasive Asian tiger mosquito Aedes albopictus: A moving target. Journal of Applied Ecology 56:2518-2527.
Imagine it’s January and you decide to go for a walk: There is snow outside, the ground is frozen, the air is balmy, geese are flying overhead, and some insect is suddenly humming around your head. It’s a mosquito. What gives?
In many regions witnessing a mosquito in winter is common. In Louisiana, mosquito season generally ends in November and starts in February. At more northern latitudes, such as New England or the upper Midwest, mosquitoes are seemingly absent for several months. But occasionally one will surprise you in the dead of a northern winter. “How can this be? Where did it come from?” you ask. As you probably expect, many mosquitoes die off when temperatures get too cold outside. But many of them don’t. It depends on the species.
Most mosquito species in Louisiana and along the Gulf Coast survive winter as eggs. Females will find a pool of water where they will lay their eggs in late fall. The adults will eventually die-off when temperatures dip below 50° F (10° C) for an extended period or if there is a freeze. The eggs enter a period known as ‘diapause’ in which their development is temporarily delayed. In early spring, the temperatures will warm enough for the eggs to continue their development, hatch, and release a new generation of mosquitoes. The species that transmits the Zika virus (Aedes aegypti) uses this overwintering strategy.
Mosquitoes swarming during summer fieldwork in Louisiana bottomlands. Video by author.
At higher latitudes, most mosquito species hibernate during winter. Like many mammals, they seek out protective coverings and hollow hiding spots to hunker down during the cold winter months. Sometimes they hibernate in your house if they get lucky enough to find a way inside. Mosquitoes are most active at temperatures above 80°F (27° C) and when it cools off, they begin to slow down. Their cold-blooded bodies become dormant below 50° F (10° C). But on warm winter days individuals sometimes emerge temporarily – this is where our lone January mosquito friend comes in. They will go back into cover when it gets cold again. In the springtime they finally leave hibernation to begin feeding and to start a new generation.
More Mosquitoes are Coming
Depending on where you live, more mosquitoes have already arrived. The tiger mosquito (Aedes albopictus) is native to Southeast Asia but was introduced to North America in the 1980s where it became invasive. Within three decades this species has expanded northward from the Gulf of Mexico, invading areas with climate unlike that of its native range in Asia. A recent study examined the impressive expansion of the tiger mosquito by comparing winter survival of populations from the center of its North American range to populations at the northern edge of its range (Medley et al. 2019). The researchers measured survival of the species’ eggs because tiger mosquitoes overwinter in egg-form. Scientists collected eggs from tiger mosquitoes in Alabama, South Carolina, and Georgia (core populations), and eggs from Ohio, Pennsylvania, and Illinois (northern edge populations). They found that the eggs from populations on the northern edge of the species’ range survived northern winters better than eggs from populations at the core of the range. Their results demonstrated the rapid adaptation of tiger mosquitoes to colder climates. The results also suggested tiger mosquitoes will continue to expand their range even farther north. Their ability to adapt within a few decades (Sherpa et al. 2019), combined with a warming climate, could lead to an increase in disease risk (Medley et al. 2019).
Focusing on mosquito control on the edge of the species’ range is one recommended method to curb their rapid expansion in the United States (Medley et al. 2019). Continuing to support research and study of these species will help scientists better understand how mosquitoes will affect us in the coming decades.
So, get used to seeing more of our mosquito neighbors in winters. They are planning on being here a while, with more of their relatives on the way.
Medley, K. A., K.M. Westby, and D.G. Jenkins. 2019. Rapid local adaptation to northern winters in the invasive Asian tiger mosquito Aedes albopictus: A moving target. Journal of Applied Ecology 56:2518-2527.
Sherpa. S., M.G.B. Blum, and L. Despres. 2019. Cold adaptation in the Asian tiger mosquito’s native range precedes its invasion success in temperate regions. Evolution 73(9):1793-1808.