What is an Asian tiger mosquito?

The Asian tiger mosquito is an exotic species introduced to North American from Asia. Officials at the Maryland Department of Agriculture say it has become a major pest and threat to public health in the state.

Since its initial discovery in Baltimore City in 1987, officials say the tiger mosquito has extended in range to all Maryland counties except Allegany and Garrett.

Tiger mosquitoes are known to thrive in areas where there is little wetland habitat. Tiger mosquitos thrive in small pockets of standing water often created by old tires, pans under plants and steel drums.

The health threat of tiger mosquitoes ranges the gambit. They are known to transmit dog heartworm disease, eastern equine encephalitis virus, dengue fever and Japanese encephalitis. Officials with the department of agriculture say lab studies have also revealed tiger mosquitoes can carry yellow fever, West Nile virus, St. Louis encephalitis and LaCrosse encephalitis.

According to the Maryland Department of Agriculture, tiger mosquitoes collected in Maryland, New Jersey and Pennsylvania in 2001 tested positive for West Nile virus.

Control of Tiger Mosquitoes in Maryland (from the Maryland Department of Agriculture)

Control of tiger mosquitoes by conventional methods in the United States has proven to be difficult. The impact of several predators and parasites as biological control agents of larvae has been investigated. In general, these agents have been found to play a small role in regulating the number of mosquitoes but not a significant impact.

The most promising predators of tiger mosquito larvae are mosquitofish (Gambusia spp.) and cannibal mosquitoes (Toxorhynchitus spp.). Fish are very effective when stocked in cisterns, water barrels and ornamental ponds, but many of the breeding sites of tiger mosquitoes are so small and cryptic as to make the use of fish of limited value.

Cannibal mosquitoes are predaceous as larvae on a wide range of aquatic organisms, including mosquito larvae. These mosquitoes are also container breeders and would seem to be an ideal candidate species as a biocontrol agent of tiger mosquitoes. A large scale "cannibal mosquito" project was initiated in New Orleans, but had minimal success in controlling tiger mosquitoes. A smaller scale project was tried in Maryland with the same result. In New Orleans and Maryland, Toxorhynchites mosquitoes were raised in the laboratory and adults were released in areas infested with tiger mosquitoes. In theory, these mosquitoes would find containers, lay eggs, and the cannibal mosquito larvae would eat tiger mosquito larvae. A fine idea, but it did not work. In Maryland, no reproduction of Toxorhynchites in the release area could be documented. The project has been discontinued.

Tiger mosquito larvae are susceptible to the toxic spores produced by the bacteria Bacillus thuringiensis israelensis (Bti). The insect juvenile hormone mimic methoprene does not kill tiger mosquito larvae, but prevents maturation to adult mosquitoes. The problem of controlling tiger mosquitoes with Bti and methoprene is how to deliver the products to the breeding sites. Due to the large number and cryptic location of breeding sites, application of larvicides is labor intensive and beyond the resources of public agency mosquito control programs.
Control of adult tiger mosquitoes by various insecticides can be effective, providing temporary relief from biting annoyance and can reduce the risk of disease transmission. Spraying is most effective when done during early evening (one hour before to two hours after sunset) and early morning (two hours before to one hour after sunrise). Those mosquitoes killed by spraying can be replaced by newly emerged adults because of the rapid breeding cycle of the tiger mosquito. In communities infested by moderate to high populations of tiger mosquitoes, adult mosquito control spraying may be necessary once per week, or more frequently, from June through September.

The most effective method of controlling tiger mosquitoes is reducing or eliminating the containers which are the source of the problem. Draining or removal of water holding containers, even on a localized basis, will produce remarkable long-term reductions in mosquito annoyance. The list of breeding sites is extensive and includes any water holding containers, but the primary sites in residential areas include clogged rain gutters, tires, buckets, cans, bottles, boats, flower pots, bird baths, outdoor statuary, ornamental pools, plastic or canvas tarpaulins, children's toys, rain barrels, and pet food and water dishes.
It is estimated that over 100,000 residential properties in Maryland provide breeding sites for tiger mosquitoes. Public mosquito control agencies do not have the resources or the legal authority to remove and drain mosquito breeding containers over such a large area.

The elimination of the breeding containers for tiger mosquitoes is largely the responsibility of the individual to conduct

thorough and repeated efforts to remove or drain all such containers on his/her property. On an individual basis, this is not a large task. The original cleanup of containers on a residential area should take no more than a few hours and periodic maintenance to keep each yard free of breeding containers will require a minimal time investment by individual residents.

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