One of the major reasons insects are so successful is because they have many physiological and biochemical mechanisms that protect them against environmental stresses—especially, freezing temperatures.
Many insects, including the common house fly and the seemingly ever-present fruit fly, produce specific proteins that offer them protection when temperatures dip below freezing. Scientists have yet to piece together exactly how these proteins function but have linked the accumulation of low-molecular-weight compounds with increased cryoprotection.
ARS scientists in Laramie, Wyoming, have identified seven unique proteins that Culicoides variipennis sonorensis produces in response to cold temperatures.
This tiny biting insect, known as a "no-see-em," transmits bluetongue virus. Bluetongue disease causes about $120 million in annual losses to domestic livestock producers, mainly in lost exports to countries that do not have the disease.
"The quantity of proteins the insects produce is proportional to the severity and duration of the cold," says Richard A. Nunamaker, an entomologist at the Arthropod-borne Animal Diseases Research Laboratory in Laramie.
Scientists say that C. variipennis produces the proteins during a process called cold-hardening. This pre-conditions the insects to withstand temperatures that would ordinarily prove fatal. Culicoides usually die after a 2-hour exposure to 14° F, but if the insects are first acclimated for 1 hour at 41° F, 98 percent of the adults survive—some for as long as 3 days.
"The cold-hardening that we performed in our laboratory is similar to weather conditions in a large portion of the United States. It is possible that adult Culicoides could survive cold weather for longer than anyone thought possible," says Nunamaker.
Some winter survivors may have been infected with bluetongue virus the previous warmer season, thus providing a possible source of infection among livestock the following spring. This potential for virus overwintering poses significant problems for people who are trying to halt its transmission among U.S. livestock.
"However, interrupting cold-hardening through genetic manipulation of Culicoides may be an effective strategy to reduce the probability of bluetongue virus survival through cold weather," says Nunamaker. — By Dennis Senft, ARS.
USDA-ARS Arthropod-Borne Animal Diseases Research Laboratory, 1000 East University Avenue, Laramie, WY 82070
"Proteins Protect Insects From Cold" was published in the September 1995 issue of Agricultural Research magazine.