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Testing the Range Limits of the Asian Tiger Mosquito
HEALTH, FITNESS, & SKEETERS
Overwintering and Collection Sites for Mosquitoes in This Study
Overwintering sites and sample locations for experimental populations. Range-core locations in white, range-edge locations in red, and field overwintering sites indicated by red box. A climate-based distribution model (sensu Medley 2010) indicates the predicted range for Ae. albopictus at the time of this study, where darker shading indicates a higher probability of occurrence. Journal of Applied Ecology, Washington University in St. Louis.
Testing the Range Limits of the Asian Tiger Mosquito
Mosquitoes push northern limits with time-capsule eggs to survive winters,
Washington University in St. Louis, August 21, 2019.
MAIN POINTS
Asian Tiger
"When the Asian tiger mosquito (Aedes albopictus) arrived in the United States in the 1980s, it took the invasive blood-sucker only one year to spread from Houston to St. Louis."
Tiger Tricks
"...the mosquitoes at the northern limit of their current range are successfully using time-capsule-like eggs to survive conditions that are colder than those in its native territory."
Time Capsule
"Mosquitoes respond to the shortening days signaling winter's onset by laying diapause eggs -- literally, delayed development eggs. These special eggs contain a fertilized embryo that's in a state of almost-hibernation and has a very slow metabolism. The result is almost like a mosquito time capsule."
"This disease vector has evolved rapidly to adapt to the United States. The fact that this has occurred at a range limit may suggest that there is potential for the species to continue to creep farther northward."
Threats
Aedes albopictus is "...a "competent vector" of numerous pathogens that are relevant to humans, including Zika, chikungunya and dengue viruses."
Egg Test
"...collected live mosquito eggs and larvae from cities near the center of the habitat they've invaded (Huntsville, Ala.; Macon, Ga.; Beaufort, S.C.) and also from the approximate northern edge of their U.S. range (Peoria, Ill.; Columbus, Ohio; and Harrisburg, Pa.)"
"Then it was time to get cold. The researchers exposed the mosquitoes to shortened periods of light to signal the onset of winter. They collected the diapause eggs that the mosquitoes produced, then dispatched batches of eggs to endure real winters in four different locations: in field sites at the northern edge and core of their current range; in a climate-controlled laboratory site that represented the "optimal" winter conditions in the mosquitoes' home territory in Japan; and in a far-north site in Wisconsin, clearly outside of the mosquitoes' current established range."
Results
"After that real winter passed, the researchers brought the eggs back into the lab and hatched them out."
"We counted all of the eggs to see how many survived the winter in all of these locations," Medley said. "What we learned was that the northern mosquitoes' diapause eggs survived northern winters significantly better than the southern mosquitoes' eggs did."
"Nobody survived that Wisconsin winter."
But…
"Based on theory, we expect that populations at range limits will be small, they will be fragmented and that they will be low in genetic diversity It's thought that these populations will not have the demographic and genetic robustness to adapt, so they remain at this state of maladaptation."
"That may not be the case with this species."
The Bottom Line
These pernacious mosquitoes will continue spreading North as the seasons continue getting warmer and warmer, as Summer gets longer, as Winter warms and shrinks down and away into more of a tropical, "wet season," than a North American Winter.
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