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WSU/Pend Oreille Extension introduced the Sense of Place series in 1999, with a focus on local landscape and natural history of Pend Oreille County, Washington. A partnership with the Kalispel Tribe of Indians Natural Resources Department has allowed us to expand this program through EPA funding to include more classes, a newsletter and this website.

A Natural History of the Mosquito


by Carol Mack

Poke at the water surface of a puddle or small pool in late spring, and it is likely that dozens of small (.2 to .5 inch) stick-like creatures will wriggle violently downward at the disturbance. These aptly named "wrigglers" are the larval stage of mosquitoes. They feed on microscopic plants and animals or organic debris in the water, filtered through brushes that surround their mouths. Larvae of most species breathe through gills at the end of the abdomen, generally resting at the water surface where they can get oxygenrich air.

Look into the water again, and you may also see some mosquito young with a much larger head, looking rather like an animated comma. These have advanced to the pupa stage and are very active, earning themselves the name "tumblers." Where wrigglers and tumblers are present, you may even be able to see eggs rafts floating on the surface-collectively they may be the size of a grain of rice. Watch long enough, and a tumbler may rise to the surface, split open, and a fully formed adult will crawl out and flyaway. For common Culex species, the entire cycle takes 8 - 10 days. You can distinguish the males by their feathery antennas-but they are not the ones to worry about. These gentle, harmless insects while away their days sipping plant nectar-helpfully pollinating some flowers in the process-and searching out females. Yes folks, it's the females that are the bad actors here. Once they have mated, they require a high protein meal before they can lay eggs. While the males are playing in the posies, the ladies are out for blood.

But how does she find you in the first place? For such little critters, the factors involved are amazingly complex (and not fully understood). Visual, thermal and olfactory stimuli all playa part. Daytime feeders may clue in visually on movement, and dark clothing probably plays a factor here in helping announce your presence. Olfactory stimuli become more important as a mosquito nears its host. Carbon dioxide is detected by mosquitoes up to 36 meters away, and lactic acid also plays a key role--antenna receptors are especially sensitive to it. But humans release up to 400 compounds trom the body as by-products of metabolism, and another 100 or so in their breath. "Whole host" odors turn out to be more attractive than a mix of carbon dioxide and lactic acid alone. It is not your imagination that some people attract greater numbers of mosquitoes than others, and that many lucky people prove to be especially unattractive. Different body chemistries at work. .. Men generally attract more bites than women, adults more than children, and attractiveness decreases as you age, according to various pieces of research. At a close range, sweat, heat and humidity draw the bugs in. Perfumed shampoos and lotions may contribute. Different species may show strong preferences for biting different parts of the body, perhaps related to local skin temperature. (There truly are "ankle-biter" species, in case you were wondering.)

West Nile Virus first appeared in the United States in 1999 on the East Coast, and put mosquitoes in the spotlight. Pend Oreille County made the news last fall with the first documented case in Washington State--a dead raven found near Newport. Most human infections of the disease are mild, but approximately 1 in 150 result in encephalitis, with advanced age being the most significant risk factor. Horses are very vulnerable to the disease--a vaccine is available and recommended.

Primarily though, West Nile Virus is a disease of birds, carried trom bird to bird by mosquitoes and mortality is very high for some bird species. Occasionally, a mosquito may follow a bird-blood meal with another meal of blood trom human or horse, and that is when there is a possibility for transmission of the virus out of the bird cycle. Washington State has 53 species of mosquitoes, in six genera. Of these, less than ten species are likely to serve as "bridge" vectors of West Nile Virus-feeding on both birds and mammals. These suspect species (see table) vary in their preferred aquatic habitats, their biting habits, and how far they will travel trom the body of water where they hatched.

Any serious attempt to reduce mosquito numbers needs to target mosquitoes at the source--the bodies of water where larval stages occur. Swatting, spraying, zapping or trapping adults only creates a vacuum that is filled by new biters almost instantly. In an area like Pend Oreille County where standing water is abundant and people relatively few and far between, effective treatment of all water bodies is somewhere between impossible and unaffordable. However, some of the culprits most likely to spread the disease to humans are the ones that lay eggs in temporary pools of water like the one you were poking earlier. Vigilance in finding these small puddles and draining them or changing the water weekly will go a long way in reducing biters near your house. (More detailed information on mosquito control is available from Cooperative Extension at 447-2401.)

How about repellents-do they actually work? The answer is a qualified yes. In fact, this is a highly researched area, and we have literature available at the Extension office that compares different formulations and concentrations from DEET, to citronella, to Skin-So-Soft for both effectiveness and lasting power. DEET (N,N-Diethyl-3Methylbenzamide) wins out for staying power and is the gold standard of repellents, used for over 40 years. The general advice is that you do not need high concentrations for it to be effective. Don't use concentrations over 10% for children, apply conservatively, and always read and follow label instructions carefully, whatever your age. Another insecticide/repellent, permethrin is very effective sprayed on clothing (not skin!) and will maintain potency for at least two weeks, and through severallaunderings. My favorite bit of repellent research describes an Alaska field trial, where a combination of permethrintreated clothing and skin-applied repellent (polymer-based 35% DEET) was compared to an unfortunate control group with no protection. The DEET/permethrin combination provided more than 99.9% protection (1 bite/hour) over 8 an eight-hour period, even under intense biting conditions, while the unprotected persons received an average of 1,188 bites per hour. (Do they pay these researchers enough?)

For more information on West Nile Virus and mosquitoes, stop by the Extension office (318 W. Scott, Newport), attend one of the free evening forums, or check the WSU Cooperative Extension West Nile Virus website: http://www.wnv.wsu.edu

Potential West Nile Virus Mosquito Vectors

Culex pipiens, Culex tarsalis: Evening and night biters, proliferate in any fresh water such as ditches, irrigated areas, marshes and catch basins, especially in artificial containers. widespread throughout Washington.

Aedes vexans: Floodwater mosquitos present in large numbers along the columbia and other rivers. bite day and night (especially at dusk), and may fly up to 20 miles.

Aedes cinerus: an anklebiter, frequently found in woodland and open meadow ponds and cattail swamps. Aggressive during the day, it does not travel far from its larval habitat.

Anopheles punctipennis: Aggressive day and dusk biters, stays near habitat--usually pools of fresh water near creeks and rivers, but may be found in artificial containers.

Coquilletidia preturbans: fierce biters, mostly in evenings. may be attracted to lights. Larva attach to stalks of aquatic vegitation and do not need to rise to the surface to breather, making control difficult.

Ochlerotatus canadensis: Found in woodland pols, a serious pest in shaded areas near breeding sites. One of the first to emerge in the spring, with adults living several months.

Culiseta inornata: cold water breeder up to 6000 foot elevations, does not like hot weather. usually feeds on livestock

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