Illinois Natural History Survey - University of Illinois

Microbial Larvicides in Mosquito Control

The next time you are scratching a mosquito bite, it may comfort you to know that mosquitoes have their problems too. Although mosquitoes can transmit human and animal diseases in Illinois, such as St. Louis encephalitis, LaCrosse encephalitis, and canine heartworm, there are many bacteria, protozoa, and fungi that infect mosquitoes in turn. Microorganisms that infect mosquitoes and other insects are known as entomopathogens to distinguish them from vertebrate pathogens such as the influenza virus. The most widely used entomopathogens in mosquito control are commercially produced bacteria. Larvicides containing these bacteria are harmless to beneficial insects and animals, but can rapidly kill susceptible larvae, which are the immature stages of the mosquito that live in water. Until recently, all bacterial larvicides targeted against mosquitoes contained the bacteriumBacillus thuringiensis serovar israelensis, but more recently a new product containing the bacterium Bacillus sphaericus strain 2362 has become available. As mosquito species become resistant to the chemical larvicides currently available, and people become increasingly concerned about the impact of chemicals on the environment, interest in the use of bacterial larvicides as alternative control agents for mosquitoes has increased.

One of the primary activities of the Survey's Medical Entomology Program has been the investigation of methods to control mosquito larvae in used tires. Used tires pose a unique problem for mosquito control because they do an excellent job of holding water. Over 10 million used tires are discarded in Illinois each year, and a single tire can produce as many as 1,000 adult mosquitoes. One species of woodland mosquito, Aedes triseriatus, breeds in treeholes and tire piles throughout Illinois, and transmits the virus that causes the human disease LaCrosse encephalitis.

corncob.gif
Corn granules coated with bacterial larvicide.

Three other species of mosquitoes that use tires as larval habitat--Culex restuansCulex pipiens, and Culex quinquefasciatus--transmit the virus that causes St. Louis encephalitis in man. Also, waste tires serve as home for a new invader, Aedes albopictus (Asian tiger mosquito), which can also transmit several viruses to man. The Medical Entomology Program has conducted numerous studies evaluating methods to apply larvicides in an environmentally friendly manner. Thanks in part to research conducted by this program, all manufacturers have adopted corncob granules as carriers for larvicides. These granules break down rapidly in the environment, and their use provides an additional market for corn products. Currently, in collaboration with Abbott Laboratories, an Illinois-based company, we are evaluating the efficacy of a new larvicide, Vectolexreg., which contains the bacterium Bacillus sphaericus strain 2362. This past summer we evaluated this product's effectiveness in controlling mosquitoes in tires, and have also investigated its potential in urban environments. Preliminary data indicate that this product provided excellent control when applied to tires containingAedes triseriatusCulex restuans, and Culex pipiens larvae. Within the city, Bacillus sphaericus controlled Culex restuans and Culex pipienslarvae in catch basins. If our results are confirmed, this bacterium will become an alternative to the chemicals currently used to treat catch basins.

In addition to these applied studies, we are also investigating the use of a new technology, cellular fatty acid analysis, to "fingerprint" commercially produced larvicides. This research is being done in collaboration with Dr. A. Ray Smith at the UIUC College of Veterinary Medicine. These fingerprints will enable us to determine the length of time that a single treatment persists in tires, as well as evaluate the impact of microbial larvicides in sensitive wetland habitats. Recent studies conducted in the field indicate that microbial larvicides can persist for as long as one year in used tires, and in some instances, recycle in tires as well. This last point is important because it raises the possibility that a single treatment may not only last one summer but carry over into the next year.

Joel P. Siegel and Robert J. Novak, Center for Economic Entomology



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Last Modified 11/05/96



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