Aggressive New Species Can Survive Harsh Midwestern Winters
WASHINGTON (AP) _ An aggressive new mosquito species imported into the United States from Asia can survive harsh Midwestern winters, an indication the disease-carryi ng insect also may establish itself in northern states, scientists said Thursday.
Researchers at the University of Notre Dame and the federal Centers for Disease Control said the Asian tiger mosquito can lay eggs that are hardy enough to survive winters in northern Indiana and Ohio.
North American strains of the mosquito, called Aedes albopictus, appear to be the types found in the more temperate parts of Asia rather than tropical areas. While cold kills adults and larvae, the insects sustain themselves in an area by leaving eggs that hatch in the spring, scientists said.
Because these are the strains that can survive the harsh winters of northern Japan and China, it is possible they can reach as far north as Minnesota and Michigan, researchers said.
The tiger mosquito, which prefers humans to other hosts as sources of blood, is so named because of the distinct black and white stripes on its legs and a white stripe down the top of the middle section of the insect.
In a report to be published in the May 29 issue of the journal Science, scientists said tiger mosquito eggs survived to hatch after wintering in controlled locations as far north as South Bend, Ind.
Drs. William Hawley and George Craig Jr., of Notre Dame, said all of the eggs from tropical strains of Aedes mosquitos died during the winter tests. However, of the five North American and two Japanese strains tested, in no case was mortality due to subfreezing temperatures greater than 22 percent.
″North American Aedes albopictus, therefore, have a degree of cold- hardiness similar to temperate zone Asian strains of this species,″ wrote the researchers, including Paul Reiter of the CDC and Notre Dame graduate students Robert Copeland and Charles Pumpuni.
″Our results imply that this northward expansion is not a transient phenomenon, but the beginning of the permanent establishment of Aedes albopictus at these latitudes,″ they continued.
Hawley said in a telephone interview that the mosquito has been found in at least 12 states so far: Texas, Louisiana, Florida, Illinois, Indiana, Tennessee, Georgia, Alabama, Mississippi, Missouri, Kentucky and Ohio.
″There is a good possibility they are up through the mid-Atlantic states as far as Virginia and the District of Columbia, but we don’t know because no one has looked for them there yet,″ Hawley said.
The insects concern scientists and health officials because they are potential carriers of viral diseases. In Asia, they carry dengue fever, a sometimes fatal disease that causes painful bone joint inflammation, and other diseases.
Hawley said dengue occurs in the United States, noting an outbreak in south Texas last year, and could become more common if it has a good insect carrier.
Laboratory tests also indicate the tiger mosquito might be a good carrier of different types of encephalitis, including the California and LaCross varieties, he said. Encephalitis causes inflammation of the brain, which can result in retardation or death.
While most mosquito-transmitted disease agents are spread from stinging different individuals, some viruses also are transferred from a mosquito to her eggs. Hawley said this raises the possibility of mosquito eggs imported from overseas bringing viruses not normally found in this country.
Researchers believe the tiger mosquito, first identified in Houston in 1985, arrived in used car tires imported from the Orient for recapping. Moisture in the tires made them ideal breeding grounds for mosquitos to lay eggs.
In 1985, 2.8 million used tires came to the U.S. from Asian countries infected with the mosquito, according to the CDC.
″Although the horse is out of the barn, so to speak, and the Aedes albopictus is established in this country, there is no reason to give up on trying to control the importation of tires,″ Hawley said. ″New strains, perhaps carrying disease, still could come in to make the situation worse.″