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Mosquitoes spread a number of equine diseases including West Nile virus and the eastern and western strains of equine encephalomyelitis. In an effort to protect their horses from these biting insects, owners have used management steps such as applying insect sprays or wipes, eliminating standing water where mosquitoes breed, and bringing horses into barns where electric fans stir the air to discourage flying insects. Large areas around houses and barns were sometimes sprayed with chemicals that repelled mosquitoes. No control measures were completely effective, and most required a continuously repeated effort throughout the warmer months.

Through collaborative research conducted at the University of Kentucky, a biological control method to reduce Asian tiger mosquito populations has been developed. The effort was spearheaded by Stephen Dobson, a professor of medical and veterinary entomology. Jimmy Mains, a former graduate student, assisted in the project and has now received both his doctorate and a National Institutes of Health grant to conduct field trials of the control method.

The Asian tiger mosquito carries West Nile virus, several encephalitis strains, and other diseases that can affect horses, dogs, and humans. This control measure uses non-biting male mosquitoes that are released across a property to mate with and sterilize females by infecting them with Wolbachia bacteria. This naturally occurring microbe infects numerous insect species, affecting and often disrupting normal reproduction. (Using Wolbachia for mosquito control is not a new concept, but targeting the Asian tiger mosquito, a recently introduced species with a rapidly growing population, is a novel application.) This mosquito breeds well in water-filled containers frequently found near houses and barns. Bird baths, flower pots, gutters, and tire ruts often contain enough water to allow larvae to develop and hatch.

Dobson breeds mosquitoes in the laboratory. After removing the females, the team releases the infected males across a property. As the males mate with wild females, they transmit the bacteria, interrupting the production of viable eggs. This eliminates the need for chemicals that may affect other insects, some of which are desirable in gardens and ornamental plantings.

If the technique proves effective in lowering mosquito populations around barns and pastures, this could be a breakthrough in decreasing the spread of several neurologic diseases that affect horses and humans.

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