Reproduced from Wing Beats of the AMCA, the official publication of the Florida Mosquito Control Association. Please use the following citation when referring to this article:
Walker, N. 1992. The eastern treehole mosquito, Aedes triseriatus. Wing Beats, Vol. 3(2):17.
(Note: See also Morphological Comparisons of Aedes/Ochlerotatus species.)
DR. NED WALKER
Aedes triseriatus is not the mosquito that you slap in the evening, or the one that has Joe Public on the phone all summer long with complaint calls. It just isn't all that abundant in most places in its range. Aedes triseriatus never drew much attention until it was found to be the vector of La Crosse encephalitis virus. La Crosse encephalitis is primarily a problem of children in the upper Midwest and east. Symptoms can range from a mild flu-like illness to seizures and coma. Ohio leads the nation in number of cases, followed by Wisconsin, Minnesota, Illinois and Indiana. Outside this "LaCrosse encephalitis crescent," cases occur in Texas, North Carolina, Michigan, Missouri, Iowa, West Virginia and New York.
Aedes triseriatus occurs from Florida, north to Ontario and Quebec, and west to the Dakotas and Texas. From north to south, the species experiences quite a range of temperatures and conditions, and it has successfully adapted to local requirements.
The tarsi and proboscis are uniformly dark. Silvery scales cover the sides of the thorax and are the most diagnostic characteristic. The abdominal segments are dark and unbanded.
Even though the accepted common name for "Tris" is the eastern treehole mosquito, it also breeds in tires, mainly in shaded locations. It can be found in a single water-filled tire behind the garage or in a tire dump with thousands of tires. In scrap tire yards, adults reach incredibly high numbers, as many as 60,000 females per acre in mid-summer. Aedes triseriatus has become an important urban mosquito because of its association with scrap tires.
In addition to the Asian tiger and yellow fever mosquitoes, Tris larvae occur with a variety of Culex and Anopheles mosquitoes. One mosquito, Toxorhynchites, which preys upon Tris larvae can be a major factor regulating the population dynamics of Tris in treeholes and tires.
One of the most interesting aspects of Tris' biology is its diapause and hibernation during the winter. Eggs are laid singly on the side of natural and man-made containers. In the north, Tris overwinters as eggs. Beginning in mid-August, eggs "sense" that daylight is getting shorter. The eggs then switch into diapause and will not hatch even if flooded. Diapause prevents eggs from hatching when larvae will not have enough warm weather to complete their development. The eggs hatch in the spring when temperatures rise and rains draw up water levels. In the south, both eggs and larvae overwinter.
The amount of food available in containers greatly influences the production of Tris larvae. If plentiful, larvae survive crowded conditions and withstand competition for food from other mosquitoes. In treeholes, food is deposited and mosquito waste products are flushed out with rainfall that flows over the trunk of the tree. In tires, the major food source is decomposing leaves.
Flight and Migration
The flight range of adults is rather short and often ranges only a few hundred yards from the treehole or tire pile where they are produced.
Few mosquito species feed rodents. These mammals are us too jittery and quick to sit still for that. But Aedes triseriatus, even though it bites a wide variety of mammals, including humans and sometimes birds, particularly likes chipmunks squirrels. These woodland rodents are active during the day when Aedes triseriatus is seeking hosts in the woods. Chipmunks and squirrels become infected with LaCrosse and can infect other mosquitoes that feed on them. Tris females can also pass the virus on through the eggs to the next generation thus providing an overwintering mechanism the for virus. Male Tris infected by the transovarial route can, in turn, infect females with the virus during mating, a kind of "mosquito venereal disease."
Dr. Walker is an Assistant Professor of Entomology at Michigan State University, East Lansing