An Aedes albopictus female mosquito feeds on a human blood meal. Photo by James Gathany, Centers for Disease Control and Prevention. Image source: Science News
A mosquito may not attack you with the same ferocity of a bear, but the mosquito attack is far more likely to occur.
Further drawing parallels to bears, mosquitos use a form of hibernation to survive cold winters.
Rather than burrowing into the earth and huddling for warmth in an vampiric mass of disease-bearing horror, mosquitos have evolved to lay cold-resistant eggs that lie unseen until conditions become ripe for hatching, growing and feasting.
Diapause, the insect equivalent of hibernation, can occur at any point in a mosquito’s life cycle, depending on the species in question and is, to a degree, actively controlled by the mosquito. Understanding how well diapause eggs actually perform during winter – and therefore how to estimate the risk posed by disease-carrying invasive mosquitos moving north – has remained a mystery until now.
Dr. Kim Medley, a biologist at Washington University in St. Louis, collected the eggs and larvae of the invasive Asian tiger mosquito (Aedes albopictus) in US cities across its range. Over the course of a labor-intensive field experiment, she and her colleagues discovered that mosquitos at the northern edge of their range laid far more diapause eggs than their southern kin and that these eggs survived winter far better than their southern counterparts. Her results were published recently in the Journal of Applied Ecology.
Medley’s results mean that the Asian tiger mosquito, which is known to carry Zika, chikungunya and dengue, may be seeding its northward expansion with what amounts to biological time bombs and in so doing, evading the control efforts currently used to limit the growth of mosquito populations.
Mosquitos at the northern limits of their ranges have been found to live in small, fragmented populations with low genetic diversity. Essentially, these “satellite populations” can survive their environment, but are not particularly well adapted to it.
This is good for mosquito control efforts, since different mosquito species are vulnerable to different tactics and low genetic diversity provides a smaller toolkit for adaptation.
Medley’s results, however, indicate that eggs hibernating in diapause can lead to a very sudden population shift, in which warming climatic conditions lead to a surge in mosquitos that are fairly well adapted to their surroundings. Which are also your surroundings.
In light of her findings, Medley suggests that control efforts shift from targeting satellite populations to a focus on preventing the circulation of mosquitos into locations along the edges of their range and to aim removal efforts at areas surrounding local populations.
Such efforts are not small and will require large‐scale collaboration among control agencies and research institutions, and should begin in the northern US range to better control Aedes albopictus mosquito populations in the face of rapid adaptation.
How rapid? It’s hard to be precise, but it only took the Asian tiger mosquito one year to spread from Houston to St. Louis, so heads up, Canada.