nature

Mosquito moves
Patricia Sullivan

It is only the female mosquitoes that bite because as egg-bearers they are in search of the nutrition that blood provides
It is only the female mosquitoes that bite because as egg-bearers they are in search of the nutrition that blood provides

TO mosquitoes, some of us are smorgasbords, and others are as tasty as cardboard. As the mosquito season begins in earnest, thereís no escaping.

Virtually, any place on Earth where the sunís long, warm rays coincide with the smallest bit of moisture, you will find some of the 3,700 species. Every time a new species bites you, your immune system goes into overdrive, often creating a big, angry welt; bites from more familiar mosquito species are smaller.

Just as not everyone attracts mosquitoes, not everyone who is bitten is bothered by the result. "Some individuals are more sensitive to bites, so they notice them more," said Jonathan F. Day, a professor at the Florida Medical Entomology Laboratory in Vero Beach, Fla. "Some people produce more cues than others. They give off more carbon dioxide. Anyone who is really active or has a naturally high metabolism. Itís more than carbon dioxide, though, or mosquitoes would waste a lot of time chasing cars."

Mosquitoes start their lives as eggs deposited in or near water, even in tiny pools that collect in the bottoms of planters or drainage pipes. A mother can lay up to 300 eggs at a time. The eggs hatch into a larvae, and after a few weeks, they turn into pupae. Within days, those pupae become adults, and if you walk into their path, you are their first meal. They usually live only a few weeks, so their interest in mammal blood is intense. Mosquitoes find you by searching, the same way a bird dog hunts birds, Day said. Only the females bite, because, as egg-bearers, they are in search of the added nutrition that blood provides. As they zero in on their victim, sight comes into play. The best targets are people in motion, those who provide a large dark target against a light background, and those who provide meals close to the ground, where low wind and high humidity favours insects.

When she lands, she probes for a capillary, then inserts her very thin and sharp proboscis through the skin. She injects you with saliva, which numbs your skin and stops your blood from clotting. Then she drinks for one to three minutes. Itís the salivaproteins, not the bite, that irritate human skin and causes the itchy bump we call a mosquito bite.

The most common native mosquitoes, those in the Culex and Anopheles genera, feed mostly after dusk, when itís easier to bite birds and mammals as theyíre settling down to sleep. The Culex and Anopheles mosquitoes also are most likely the bugs you hear buzzing near your ear as you lay in bed on hot summer nights. They spend their days in the shade of bushes, grasses or leaf litter, near the twin food sources of moisture and micro-organisms, and hidden from predators.

But the predominant mosquito is Aedes albopictus, or the Asian tiger mosquito. This black-and-white striped critter doesnít wait for dusk, as the other self-respecting skeeters do, but feeds all day long. All you have to do to trigger its wrath is stroll by the ivy or azaleas during the daylight hours and zing. Ouch. The Asian tiger targets the lower leg, between the knee and ankle, and scientists call it an aggressive daytime biter.

The latest dread disease carried by the Asian tiger mosquito is chikungunya, which a Centres for Disease Control and Prevention online fact sheet notes is usually not fatal and "has been cited as the cause of numerous human epidemics in many areas of Africa and Asia and most recently in limited areas of Europe." It "can cause a debilitating illness, most often characterised by fever, headache, fatigue, nausea, vomiting, muscle pain, rash, and joint pain." Mosquitoes transmit disease to 700 million humans every year.

So what good are mosquitoes? They do have a niche in the natural world. Their larvae and pupae are attractive food for fish and other aquatic insects, and the adults provide a tasty meal for birds, bats, spiders and dragonflies. The mosquitoes themselves feed on bacteria and algae from rocks, plants and water, as well as on birds, pets and humans.

Prevention comes in three versions: Rid the environment of the mosquitoes, block the insects from finding skin or repel them from the skin they do find.

Mosquito control districts try to eliminate the largest nesting areas for mosquitoes and aim to eliminate them when theyíre still larvae and stationary. On an individual level, most people know to drain standing water on their property every week, as the smallest bit of undrained rainwater can provide a lovely maternity ward for mosquito eggs.

ó By arrangement with LAT/WP





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