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Refuge Notebook: Bloodsucking freaks

Posted: July 4, 2013 - 5:26pm  |  Updated: July 5, 2013 - 10:22am
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Michigan DEQ photo A mosquito finishes a blood meal.
Michigan DEQ photo A mosquito finishes a blood meal.

Almost overnight, the mosquitoes came out in force across the Kenai Peninsula, leading to shortages of insect repellent and general discontent during outdoor activities. The rapid onset of cold temperatures last fall followed by an insulating snow blanket created ideal overwintering conditions for hibernating mosquito species. Combined with a late, cool spring, abundant standing water conditions, and a warm uptick in temperatures, the stage was set for an extreme (and annoying) mosquito boom this summer.  

Not all species appear at the same time — Alaska has around 35 species of mosquito that emerge in order throughout the season. The first species to emerge is one of the large “snow mosquitoes” that overwinter as adults and come out of hibernation with snow still on the ground. Adults hibernate in leaf litter, under downed trees, or in other protected natural places. Other species overwinter as eggs, with adults emerging in mid- to late summer. Worldwide, there are over 3,500 species of mosquitoes, of which only a couple of hundred or so bother humans.  

A mosquito can drink up to three times its weight in blood, but don’t fret — it would take about 1.2 million bites to drain all the blood from an average human body. Only the female sucks blood, and most mosquitoes require a blood meal to develop eggs. Some autogenous species can produce eggs with no blood, and others can lay up to three broods of eggs, becoming increasing voracious for blood with each brood. They pierce the skin with a serrated proboscis and draw blood through one of two tubes, while pumping fluid containing a mild painkiller and an anti-coagulant through the second tube. Most people have minor allergic reactions to the fluid, causing the area around the bite to swell and itch. Both female and male mosquitoes also feed on plant nectar. 

Eggs are deposited in clusters in stagnant water or forest floors with spring flooding, making much of the western Kenai Peninsula a paradise for breeding. In warm weather, eggs can hatch within 2 to 3 days into larvae, which feed on organic matter and breathe oxygen from the surface. Larvae stay in this stage from 4 days to 2 weeks, although they can survive for a month in near-freezing water. They develop into pupae, which are non-feeding and partially encased in cocoons. Over several days, the pupae change into adult mosquitoes. 

Mosquitoes buzz around best in calm weather, but can function in wind speeds up to ten miles per hour. They don’t roam far — a memorable study in 1997 released 3 million radioactive mosquito adults from a single spot. After a week, no specimens were found more than 600 feet from the point of release, and after a month only one was recovered from as far away as 5,000 feet. Natural predators include bats, fish, insect species such as dragonflies and water beetles, and birds — if you keep chickens, you can watch them enthusiastically devouring mosquitoes in your yard. 

Mosquitoes seem to prefer some victims over others. They cue in on carbon dioxide, which is produced at different levels by different people. Other signals include higher body temperatures, scents and odors, alcohol (even a 12-ounce beer can apparently make you tastier), and even pregnancy, as expectant mothers exhale more carbon dioxide and tend to have higher temperatures. Some studies show certain blood types exude chemical markers that attract more bites. 

These insects are feared not only for their dreadful whine and itchy bite, but for their capacity to carry and transmit diseases such as bird flu, West Nile virus, malaria, and encephalitis. Human disease carrying capacity is thought to be low up north. Researchers from San Francisco State University are currently testing thousands of mosquitoes captured in Anchorage, Fairbanks, and Coldfoot for presence of malaria, after this disease was detected in non-migrating black-capped chickadees in Anchorage and Fairbanks in 2011 and 2012. Since these birds don’t migrate, they were been bitten by an Alaskan mosquito carrying the malaria parasite. The types of parasites that cause malaria in birds don’t infect humans, so there is currently no cause for alarm.  

After outbreaks of West Nile virus in other parts of the country, the Alaska Department of Fish and Game conducted extensive testing of birds for presence of the virus, which can be spread to humans by mosquitoes that first bite an infected bird. To date, no evidence of this virus has been found in Alaska. Fortunately, conditions are thought to be nearly impossible for this virus to exist up north because migratory birds are gone by the time major mosquito species hatch. The virus needs about 10 days to incubate in the bird before it can be spread to mosquitoes.

The best way to minimize bites is to cover up and put on repellent — wear tight weave cotton shirts and pants in khaki or neutral colors, tuck in shirts and pants, and use a head net in severe conditions. We can also take comfort in that in a few short months, our mosquito friends will be back in hibernation, having fulfilled their ecological niche of bloodsucking dominance for the summer.   

Dr. Elizabeth (Libby) Bella is an ecologist at Kenai National Wildlife Refuge. You can find more information about the Refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.

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