Bedford County Conservation District

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West Nile Virus

Mosquito Biology and West Nile Virus

Mosquitoes have a life cycle with four major stages, egg: larva, pupa, and adult. Often called complete metamorphosis, similar to moths and butterflies, only the adult stage, as a blood-feeding female, is capable of transmitting disease. Larval and pupal stages are aquatic, and different species use different water habitats. Some mosquitoes are found in relatively clean waters of permanent wetlands or bogs but the greatest numbers of nuisance and disease-carrying types are found associated with stagnant waters, floodwaters, and habitats created by man. The larval stage feeds and grows, passing through four stages or instars of increasing size , molting into a new skin with each. After the 4th instar, the larva enters a transformative stage as a non-feeding pupa from which will emerge the flying adult. Adult mosquitoes of both sexes feed upon flower nectar with their long proboscis mouthparts. Only the female takes a blood meal, after mating, requiring the extra nutrition to complete the reproductive cycle and lay eggs.

There are more than 50 species of mosquito in Pennsylvania and not all are implicated in spreading West Nile virus or any other diseases. The West Nile virus, like other encephalitis viruses such as Eastern Equine encephalitis (EEE) and St. Louis encephalitis (SLE), uses two hosts through its life cycle, a mosquito and a bird. This is the 'normal' transmission cycle for these viruses. Disease oubreaks can occur when infected female mosquitoes shift from birds to humans or horses for their blood meal.

 

Protecting Youself

Reducing your risk of contracting an illness due to West Nile Virus begins with eliminating mosquito-production habitat around your home. Stagnant water standing in even the smallest container can provide a home for mosquito larvae. Water that stands in ditches or in low spots after a rain, particularly if grass clippings or other organic debris are included, can be attractive to the Culex species that most often carry WNV. Old tires should be recycled or stored under cover where rain and snow cannot enter. Toys, tin cans, buckets, wheelbarrows, flowerpots, bird baths, and kiddie pools are all items frequently found in yards, often holding water, and capable of breeding mosquitoes. Another breeding site often overlooked are clogged rainspouts. Clean these and make sure that water is draining properly. Sites that cannot be dumped or drained, such as ornamental ponds or low lying areas of lawn, can be treated with over-the-counter products containing Bti, a biological control containing a naturally-occurring bacteria that kills mosquito larvae but is not harmful to people, pets, fish, or plants.

For protection against mosquitoes already flying and biting, window screens and screen doors protect us inside our homes. When outside, wear long pants and long sleeves and use insect repellant according to directions (products containing DEET have been found most effective). While the Culex mosquitoes most often found infected with WNV are most actively seeking blood meals after dusk and before dawn, many other species will bite during daytime hours when their habitats, such as wooded areas of floodplains along streams, are invaded. Avoiding the times and places where mosquitoes are most likely to be encountered should be part of our personal protection strategy against biting mosquitoes.

Reporting Mosquito Complaints

Problems with mosquities in your neighborhood should be reported to the DEP West Nile Virus Program by calling Jennifer Stough at 814-705-4970. Further information on mosquitoes and West Nile Virus can be found at the links below.

Link to PA DEP WNV page.

Link to Center for Disease Control WNV page