The month of May in metropolitan Washington set records and near records as one of the driest Mays on record. However, with the return of showers in the past week, natural vessels like tree holes and containers including water-filled wheelbarrows provide perfect conditions breeding mosquitoes. Legions of mosquito larvae, called wrigglers, are hatching from eggs deposited by the females.
Wheelbarrows and pails filled with water are breeding sites for thousands of mosquitoes.
Wrigglers are beautiful swimmers and feed by filtering small particles from the water with a set of mouth brushes reminiscent of Groucho Mark’s mustachio. They breathe through a snorkel-like tube on their rear end that pierces the water’s surface. Mosquito wrigglers shed their skin or molt between the four larval stages before turning into a tumbler, the pupal stage of the mosquito. Within just a day or two, the pupal skin splits open along the midline and the adult mosquito rises wraithlike from the shell. After the wings have expanded and hardened the mosquito flies to find a meal. During the first several days of adulthood, both males and females feed on carbohydrate rich food such as plant nectar or aphid honeydew. These sweets remain the source of food for the entire life of the male mosquito. The female feeds intermittently on natural sugars, but between bouts of sugar-snacking she has a blood lust. Female mosquitoes use animal blood as the source of protein to produce eggs. After mating and taking a blood meal, eggs develop within the abdomen of the female. The pregnant mosquito lays her brood in a water-filled container such as a tire, pail, or bird bath. Some, like the ferocious Asian tiger, Aedes albopictus, lay eggs near the water line. When the vessel fills with rainwater, eggs hatch and larval development begins. Others, such as the Northern house mosquito, Culex pipiens, lay eggs in rafts that float on the surface of the water. Each raft can contain more than 150 eggs.
Many species of mosquitoes prefer to feed at dusk and you can avoid being bitten by staying indoors in the evening. Unlike many of our native mosquitoes, the exotic Asian tiger is a daytime biter, adding new hours of itching, scratching, and swatting to summer days in the garden. Mosquitoes are more than just a nuisance and several species carry important diseases such as West Nile Virus.
Protect yourself from aggressive biters by wearing light-weight, long-sleeved shirts and pants when working outdoors. Certain brands of clothing are pretreated with mosquito repellents such as permethrin. I have worn these in tropical rainforests where mosquitoes were ferocious and received nary a bite. Many topical insect repellents can be applied to exposed skin before you go outdoors. Some will provide many hours of protection, while others provide virtually none. Some repellents should not be applied to children and you should always help kids apply repellents. Do not apply repellents containing DEET under clothing. For safety, be sure to read and follow the directions on the label of the repellent before you apply it to people or clothing. Many traps are also available to capture and kill mosquitoes. Some rely on a light source to attract the blood seekers. Although many types of moths, crane flies, and beetles are attracted to light, mosquitoes, unfortunately, do not use light to find their meals and are not readily attracted to light traps. One study demonstrated that less than 1% of the insects attracted to light traps were biting flies such as mosquitoes. This study estimated that light traps kill billions of harmless and beneficial insects each year. Actually, mosquitoes are attracted to odors emanating from the host. As we move about the earth, we release many odors including carbon dioxide and lactic acid used by hungry mosquitoes to find us. Some mosquito traps release carbon dioxide and will catch many mosquitoes. Much work remains before we fully understand how well these traps reduce bite rates or control mosquito populations in an area. To reduce the chances of mosquitoes breeding around your home, eliminate standing water by cleaning your gutters, dumping your bird bath twice a week, and getting rid of water filled containers such as cans, wheelbarrows, and other containers. If you have an aquatic water garden or standing water on your property that has no fish in it and is breeding mosquitoes, you can use a product containing the naturally occurring soil microbe known as Bacillus thuringiensis isrealensis a.k.a Bti. Bti comes formulated in doughnut-shaped tablets that can be placed in water to kill mosquito larvae. Battalions of biters are about to make their presence known. Get ready to protect yourself.
References
We thank Desiree Adib, Eric Noll, and Allison Girvin for providing the impetus for this Bug of the Week. To learn more about the mosquitoes and how to defeat them, please visit the following web sites:
http://www.agnr.umd.edu/users/charlesmg/mosquito/insect_menace1.html
http://www.cdc.gov/ncidod/dvbid/westnile/index.htm