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Mosquitoes - "How to Decrease the Numbers"

Sanborn Weekly Journal of Woonsocket, South Dakota

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"It is that time of year when the mosquito population, especially those carrying West Nile Virus begins to take hold. One of your first modes of protection is the use of personal mosquito repellents. There are two types of chemical repellents: DEET and Per-methrin. DEET is the chemical found in most sprays. It is safe at the rate of 10 percent or less for children 2-12 and in adults for four hours of protection a single thorough coat a product containing 20 percent DEET will suffice. Permethrin is a man-made chemical that kills mosquitoes on contact by disrupting their nerve cells. It is only to be applied to clothing 2-4 hours of being worn. The product for use on clothing contains 0.5 percent permethrin. As a side note permethrin at a lower concentration (0.25 percent) is also used in insecticidal shampoos for children infested with head lice.

Adult mosquito control is not the most effective way to reduce mosquito numbers. Removing standing water and controlling larvae is the primary means of mosquito control around the home and yard. With our extremely wet summer so far, removing standing water is not an easy task. Just an inch of water in the bottom of a forgotten tin can be a hatching site for hundreds of mosquitoes. First thing to do around your house is to check on areas that may hold water. You will need to remove them, prevent them from holding water or dump and refresh the water every week. Under ideal conditions mosquitoes can go from egg to adult in less than 10 days.

If water sources cannot be drained or refreshed, consider covering small containers. Aerating the water or stocking insect-eating fish in backyard ornamental pools or nearby ponds may help. Removing weeds in and around the pond also may help cut mosquito numbers in some locations. Clearing out the vegetation opens up the water to wave action by wind. Water that is agitated by waves will reduce mosquito larval survival; they will drown since they breathe air by attaching themselves to the water's surface. Some larval control products are available that produce a thin film over the water surface. These films either prevent the larvae from breathing or reduce the surface tension of the water, causing them to drown.

The most common products available to homeowners for controlling mosquito larvae contain proteins derived from Bacillus thuringiensis subsp israelensis or Bti. These products are commonly sold as granules or pre-formed blocks that release the Bti protein when placed in water. The Bti protein is toxic only to mosquito wrigglers and the larvae of certain aquatic flies such as midges and black flies. It has no harmful effects on humans, horses, fish, tadpoles, frogs, crustaceans, snails or other non-target aquatic animals. Formulations of Bti are available that last from as little as three days to as long as 30 days. Products containing Bti are an excellent choice for stagnant water areas that cannot be drained. Larval products containing methoprene are also available. These products act as insect growth regulators and prevent the pupae or tumblers from maturing into adult mosquitoes. Both methoprene and Bti products become less effective as mosquito larvae mature. The products are ineffective against adult mosquitoes. Some product names are Mosquito Dunks, Mosquito Bits, Vectobac and Vectolex.

When treating adult mosquitoes it is typically just to decrease numbers for a short time because there is short or no residual control. This will reduce the population in the treated area but others can fly in from five or more miles away. A home barrier treatment generally is an application of a labeled insecticide onto mosquito resting areas around the yard and home with an ordinary household sprayer, hose-end sprayer, or ready-to use container equipped with a spray gun.

The most common insecticides for home use contain the active ingredients bifenthrin, cyfluthrin, deltame-thrin, lamda-cyhalothrin, or permethrin. Apply the insecticide to surfaces where mosquitoes will be resting during the day—the north or sheltered sides of board fences, wall siding, eaves and outbuildings; trees and shrubs; under decks; and in tall grass or weeds. Apply in advance of the planned activity so that the treated surfaces are completely dry before use. Spray objects and structures; just wetting the lawn with insecticide is not effective.

Other adult mosquito control are carbon dioxide - baited traps and bug lights. For more info on these two types of control and other information about mosquitoes please see your local extension office.

Copyright 2009 Sanborn Weekly Journal, Woonsocket, South Dakota. All Rights Reserved. This content, including derivations, may not be stored or distributed in any manner, disseminated, published, broadcast, rewritten or reproduced without express, written consent from SmallTownPapers, Inc.

Original Publication Date: July 23, 2009

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