Hungry Mosquitoes Looking for Unwary Hosts After June Rains

By Nathan Riggs, Extension Agent – IPM, Texas Cooperative Extension


Photo: Drees-TAMU Entomology

July 2004 is beginning in a similar pattern to July 2003, except that we are one week removed from heavy rainfall across the area. While the benefits of the rainfall are numerous, let us not forget that the local insect fauna such as fire ants and mosquitoes are enjoying the moisture as well.

Mosquito life cycle

Photo: Illinois Dept of Public Health

One can’t think of rain without thinking of the hoards of blood thirsty mosquitoes that appear a few days after. Mosquitoes lay their eggs in watery tree holes, puddles, containers, tires and any other site that could hold water for 7 to 10 days. The eggs hatch into larvae that feed on algae and other microscopic plants. After 2 to 3 days, the wigglers develop into a pupal stage that wiggles as well. In another 2 to 3 days, an adult mosquito emerges; ready to take on the world. Adult male mosquitoes feed on nectar from plants and do not feed on blood. The females feed on blood from animals, people and birds. At this time in San Antonio, we are in a prime active period for emerging mosquitoes.

There are 57 species of mosquitoes that call Bexar County home, but one of the most common around homes is the Asian Tiger Mosquito (Aedes albopictus). This species is an aggressive biter and likes to harbor in ground cover, shrubbery and in flowerbeds. With all of this in mind, there’s still the hotbed question, “What can I do to control mosquitoes around my home?” Adult mosquitoes can fly up to two or three miles from their breeding sites, so controlling adults in the lawn may not last longer than a couple of days. However, treating the places they hide during the day will provide relief. Adult mosquitoes need high humidity and locations with ivy, groundcover, shrubbery or hedges fit the bill. There are a wide variety of non-mix products that can be attached to a water hose and sprayed on these locations.

Mosquito larvae

Mosquito larvae naturally hang upside down from thesurface of any appropriate water source. Photo: University of Rhode Island

Overall, products containing permethrin, malathion or pyrethrins are the best bets for controlling adult mosquitoes in vegetation. Mosquitoes develop in standing water from tires, unused swimming pools, water gardens, flower pot saucers, pet dishes, tree holes, puddles, clogged rain gutters and other standing water sources. Refresh your pet’s water dish at least every other day with clean water. Be sure to dump out standing water where possible and use a larvacide such as “Mosquito Dunks” or “Mosquito Bits” to control wigglers in water gardens, ponds, ditches and other areas. They are non-toxic to fish or animals that would live in or drink the water. Dunks will control wigglers for up to 30 days and Bits will work for 14 days. Either of these products are available at nurseries, feed stores, hardware stores and large retailers such as Home Depot or Lowe’s. Some nurseries are beginning to carry liquid versions of these products for spraying in areas where water stands.

With the ever-present threat of West Nile virus now entrenched in San Antonio, using mosquito repellants will provide a measure of relief against mosquito attacks and reduce the chances of virus infection from bites while outdoors. In a study published by the New England Journal of Medicine, the DEET-containing repellant “Deep Woods Off!” provided 301 minutes of continuous protection before wearing off while Sawyer Controlled Release, another DEET-containing product, provided 234 minutes of repellency. A popular non-DEET repellant, Avon’s Skin-So-Soft Plus, provided just 23 minutes of relief before bites occurred. There are newer repellants on the market that contain cedar oil and other aromatic plant oils. These should provide at least a few minutes’ worth of relief, but none have been tested by The Journal.

Some callers to the Extension office have asked about the carbon dioxide mosquito trapping devices. Here’s the skinny on these: they WILL catch mosquitoes of the conditions are good. Good conditions are relatively still air and a location that is habited by dense vegetation and high humidity: a perfect place for adult mosquitoes. A back yard with lots of shrubbery and ground cover combined with shade will fit this description. Having said all of this, the success rates of these devices are running about 50-50. Some of the machines contain a special lure chemical called octenol that is more attractive to certain species of mosquitoes, implying a much better chance of catching more of the little vampires. One thing to remember, though: the Asian Tiger Mosquito is not attracted by octenol and therefore would be less attracted to the device than without the lure.

The most important factors for reducing the potential for mosquito bites are dumping out standing water where possible, wearing repellants when outdoors at dawn or dusk and treating areas where adult mosquitoes harbor during the day. Following these suggestions will make your outdoor experiences more enjoyable and will reduce your chances of being a mosquito blood donor!

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