Wednesday, March 31, 2010

Mosquitoes or Midges?

Large numbers of non-biting midge flies (Family Chironomidae) are being reported this time of year. These midges can be easily confused with mosquitoes, since these midges are small, between ⅛- ½ inches in length. However midges lack scales on their wings and do not have a piercing mouthpart, like mosquitoes. Adult midges are humpbacked, are brown, black, or gray in color, and male midges have very feathery antennae. Sometimes in urban environments, where structures are built next to lakes, rivers, stagnant ditches and ponds, adult midges can emerge in extremely large numbers. These swarms tend to occur just after sunset, as the adults become active and fly towards outdoor lights. Adults are attracted to lights and may accumulate in large numbers on window screen, around porch and street lights. Swarms of adults may be so dense that they interfere with outdoor activities and can stain walls and other surfaces when they rest. They can also enter into structures through small cracks or deep piles of dead midges can accumulate underneath outdoor lights.

Chironomid midge eggs are laid on the surface of the water, and then the eggs sink to the bottom and hatch. The larvae burrow into the mud and construct small tubes to live in. The organic matter in the water and in the mud serves as food for the developing larvae. Some larvae are known as "bloodworms" due to the presence of hemoglobin in the blood that allows the larvae to breathe in low oxygen conditions in the mud. Larvae transform into pupae while still in their tubes and then the pupae swim to the surface where the adult emerges. Adults mate in swarms soon after emerging. The males swarm at dusk and mating occurs after females enter the swarm. The adults only live for a few days since they do not feed.

Some Control Options

Some Non-Chemical Control Options:

1) Fertilizer run-off from residential lawns and garden, golf courses and agricultural fields are sometimes responsible for the development of larger populations of midges; so the proper use of fertilizers can avoid excess run-off into lakes, ponds and streams.
2) Locating the source of breeding is advised so all areas of standing water should be eliminated. Midges may fly as far as a quarter of a mile from the breeding site such as a drainage ditch, standing water, lake or pond.
3) High intensity white light has been found to be highly attractive to adult midges so by keeping blinds closed and porch lights off will help to reduce the number of adults attracted to these outdoor lights.

Some Chemical Control Options:

Bacillus thuringiensis var. israelensis (Bti), is registered for use against chironomid midge larvae. Also insect growth regulators such as methoprene can be used to control midge larvae. In addition, applications of residual insecticides such as those containing permethrin can be applied to porches, carports, under the eaves of structures to control adult midges.

Photo of a midge, Family Chironomidae. Photo by Marilyn Sallee, Master Gardener Entomology Specialist, Tarrant County.