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Auburn, Aug. 17---Fall is the peak season for yellow jackets in Alabama. Many people are already encountering and even experiencing painful stings from these wasps during outdoor activities.

Yellow jackets are black-and-yellow social wasps. Hornets and yellow jackets are the most common wasp groups, says Dr. Xing Ping Hu, an entomologist with the Alabama Cooperative Extension System. Hornets usually construct exposed nests in the branches of trees and shrubs or on recessed structures. They also may construct nests in cavities.

Most of the yellow jacket species are ground nesting. However, some nest in buildings or in tree cavities and structural voids.

Yellow jackets begin new colonies by mated overwintered females who become foundress queens. The new nests, which are usually constructed in May, may contain a dozen developmental cells. By fall, annual nests typically contain 300 to 120,000 developmental cells, depending on the species and environmental conditions.

However, in south Alabama large perennial colonies have been maintained by some species and are ruled by multiple queens, tended by thousands of workers and contain millions of cells, says Dr. Hu.

The most useful tool for managing yellow jackets is arguably, a dust applicator, Hu says. Hand dusters and air dusters are the more common applicators. These should be operated by a pest control professional who wears protective garments.

Dr. Hu says the advantage of using a dust formulation is that the dust can be carried by air deep into cavities and voids of wasp nests. The dust particles remain on the concealed surfaces, awaiting contact with foraging yellow jackets, which, in turn, contaminate other nest mates.

Using wettable powder insecticides in surface-treating yellow jacket nests can accelerate the colony-elimination process. This permits sameday nest removal, says Hu.

"If aerosol and mist insecticides, such as pyrethirins and other botanical extracts, are used, they should be applied to nest cavities after dark when nest members are contained within the treatment zone," says Hu.

Although it is necessary to close off multiple entry points of wasps from structural voids to the living and work species, homeowners should never caulk close an exterior entrance to an active yellow jacket nest in a structure. This action only alarms the trapped wasps and causes them to seek out alternative escape routes to the outdoors.

Remember, all female and worker wasps and bees can sting repeatedly, except for honeybees, says Hu. With occasional stings comes the likelihood of increased sensitivity to venom. Also, remember to be cautious of small areas bare of vegetation, because they could be ground nests of yellow jackets. People should exercise care and wear protective clothing when treating wasps.