Perhaps it’s because scientists – who will travel to the remotest of remote regions, braving the most bruising conditions to unravel almost any mystery – aren’t too keen on facing Culler’s chosen subject of research: the mosquito.
These aren’t your typical skeeters. The bloodsuckers of the far north are infamous for swarms so enormous as to blot out the sky in a Hitchcockian wave of horror. The really scary thing is that scientists know little about the ecology of these insects, even as climate change reorganizes ecosystems in the Arctic, which is warming twice as fast as any place on the planet.
“There is not really a lot of Arctic mosquito research going on, which I found to be really surprising,” explains Culler, a postdoctoral researcher at Dartmouth’s Institute of Arctic Studies at the Dickey Center. Most of what is known about their natural history came from studies between the 1950s and 1970s. “It was a little bit challenging to get my research started, because I didn’t have much to go off of.”
Culler and her co-authors on a paper published in the journal Proceedings of the Royal Society B: Biological Sciences made headlines around the world in September when they announced that the population of Aedes nigripes, one of only two mosquito species in Greenland, responded quite warmly to warmer temperatures. The research was supported, in part, by a National Science Foundation (NSF) grant funding field opportunities for graduate students.
They reported that the probability of mosquito larvae surviving to adulthood could increase by more than 50 percent if average Arctic temperatures rise by two degrees Celsius, a projection based on field observations and lab experiments. Bump up the thermostat by five degrees Celsius, and the odds jump by 160 percent, despite a predicted uptick in predation by beetles as well. The Arctic has already experienced at least two degrees Celsius of warming since the 1960s, according to the National Oceanic and Atmospheric Administration (NOAA).
Mosquitoes are more than just maddening pests that bedevil humans. While squadrons of females hunt mammals for blood meals as part of their reproductive cycle, benign males of the species help pollinate plants. Mosquitoes are also as much prey as predator, feeding other insects, fish and birds.
“I was interested in the mosquitoes because they are a very big part of the ecosystem in the tundra, and I don’t think we have a full appreciation of the role they play,” Culler says.
Home to 34 known species of mosquitoes, Alaska is legendary for its summertime swarms. Derek Sikes, entomologist and Curator of Insects at the University of Alaska Museum in Fairbanks, says that military bases in the state are monitoring mosquitoes for disease, but no one is doing any focused ecological work on them as far as he knows. (Incidentally, while Alaskan mosquitoes are vectors for some wildlife diseases, none carry human diseases like malaria. Ditto for the Greenland species.)
Sikes notes that mosquitoes aren’t the only bugs in the Arctic whose populations spike violently. In 2006, for instance, yellow jacket numbers increased tenfold in Alaska.
“We don’t really know what drives these outbreaks because each species has a different niche,” Sikes says. “Mosquitoes like a moist spring and summer because their eggs hatch in water, and the larvae are aquatic. Areas of Alaska with permafrost are often fairly wet because the water can’t drain into the soil, and this provides a perfect breeding ground for mosquitoes.”
Robbie Score doesn’t necessarily care what causes the swarms. She just hates the little buggers.
“I keep every inch of myself covered, no matter how warm it is out,” says Score, who has supported Arctic research for nearly a decade as a member of Polar Field Services, currently as the IT & Special Projects manager.
Her coping strategy: “If I am not wearing a head net, then I wave my arms in front of my face a lot. You have to keep moving, [and] pray for a slight breeze.”
On a trip outside the small town of Kangerlussuaq (Kanger) in western Greenland, Score recalls visiting a lake with a research team in a very boggy area. “The mosquitoes were horrendous. The constant sound of the ‘zzzzzzzzzzzz’ was mind numbing. I looked at my companion, and she was totally black from being covered with skeeters.”
It may not get any better.
Culler says temperature measurements and other data since the 1970s show that the long-term trend is not just about higher temperatures; the melt season is shifting earlier by two days per decade. While there is much variability from year to year – for example, ponds near Kanger thawed two weeks earlier in 2012 compared to 2011 – the prediction is that the Arctic and its biological systems are slowly but surely being reshaped.
One stark example of that can be found on an unrelated project, also supported by NSF, involving a team of researchers examining the effects of warming on the Alaskan tundra ecosystem. Specifically, scientists are studying how vegetation changes across the tundra and long-term seasonal changes affect how migratory songbirds find food and shelter. In addition, team members like Ashley Asmus, a graduate student at the University of Texas Arlington, are looking at the effects of increased shrubbery over tussock-tundra on the arthropod food web – including mosquitoes.
“At the moment, we don’t know much about how mosquito populations respond to shrub abundance,” says Asmus, who employs a huge reverse leaf blower to collect bugs from the tundra like a housekeeper vacuuming crumbs off the carpet.
“We do know that total plant-dwelling and flying insect biomass … tends to be greater in shrub habitats compared to tussock-tundra,” she explains. “This makes sense, because shrub habitats have greater plant biomass, and so should support more insect biomass. What is unknown is how much of the difference in insect biomass comes from an uptick in mosquito population size versus the many other insect groups that knock around the tundra, like houseflies, plant-eating bugs, spiders and wasps.”
The five-year-long project – led by Natalie Boelman at Lamont-Doherty Earth & Environmental Institute at Columbia University, Laura Gough at Towson University and John Wingfield at University of California-Davis – monitored four sites between 2010 and 2014. One undergraduate team member is counting and weighing mosquitoes from samples collected during that time.
“My speculation is that an increase in the habitat structure in shrubs – think about all those sticks and leaves – may provide shelter to mosquito populations during cold or windy weather. So, we expect to find less up-and-down variability in their population size within summer seasons in shrub habitats,” Asmus says.
Meanwhile, Culler is moving on to the next set of questions regarding mosquito ecology in a warmer and greener Greenland. For example, while the swarms appear large, sources of blood meals for females are relatively scarce due to the low density of mammals like the caribou; successful feeding by a female vastly improves reproductive success. (The September paper did note that caribou can expect more misery in a warmer world, as mosquitoes emerge earlier during calving season to harass juveniles.)
“We’re really curious as to how many of these mosquitoes actually get a blood meal,” Culler says.
She is currently examining adult specimens to learn more about reproduction and egg laying to understand mosquito population dynamics. The next phase of that research would involve establishing a series of long-term monitoring sites to track population variation throughout the year and from year to year.
Such stations basically consist of a fan, net and CO2 tank – carbon dioxide is an irresistible perfume for female mosquitoes – that emit short bursts of the gas to bait and capture the insects. The units are small, portable and easy to use, according to Culler.
Asmus tested a different device designed by Culler last year in Alaska, though an unusually dry summer spoiled the experiment. The emergence trap is basically a hula-hoop that sits on top of the water, with a dome-shaped net on top of the hoop. As mosquitoes turn from pupa in the water to adults in the air, they are trapped in the net.
Asmus sees the units as an unbiased method to sample the mosquito population. Her question: Are the summer swarms indicative of a massive population – one estimate claims upwards of 17 trillion mosquitoes in one summer – or a matter of perception by human bait … er, observers.
“My insect vacuum sampler once captured the equivalent of over 400 mosquitoes in a cubic meter of airspace, but that airspace was next to me,” Asmus notes. “We need a better way of sampling mosquito populations in an unbiased way, if we want to figure out the ecological accounting of this system – how much biomass, and where it all goes.”
In collaboration with European colleagues, Culler hopes to recruit public assistance if she can secure funding for a large-scale monitoring project.
“Our grand vision is to have this be a citizen-science project,” she says. “It’s extremely awesome data, and it’s something anyone can do.”
In the meantime, Culler will continue to face the bloodthirsty swarms to advance science.
“I’m really excited to be working on Arctic mosquitoes, and I would love to have some collaborators working in other parts of the Arctic so we can get a bigger picture idea of what’s going on,” she says. “I think it’s super interesting and important and very timely. I’m just going to keep working on it for now, and think I’ll eventually find some folks who want to join me.”--Peter Rejcek