COLD HARDINESS OF TREE-HOLE MOSQUITOS IN THE GREAT-LAKES REGION OF THE UNITED-STATES

Among species that overwinter as larvae, fall-collected individuals were freeze tolerant, whereas all summer-collected larvae were killed by freezing. Cold hardiness varied among species and among larval stages within species. The order of diminishing cold tolerance was Orthopodmyia alba, Anopheles barberi and O. signifera. Some O. alba larvae survived freezing at -25°C, the lowest temperature reported to be survived by an aquatic animal in ice. Prolonged (up to 16 days) and multiple (4) exposures to -15°C had no effect on survival of O. alba 3rd instar larvae, but increased mortality of 2nd instars of O. alba and A. barberi. Species were more tolerant of cold when frozen in rot-hole water in which they are commonly found in nature than in "pan' water in which they rarely occur. Both photoperiodically induced dormancy and prefreezing exposure to low temperature were necessary for establishment of cold hardiness in laboratory-reared A. barberi. Eggs of Aedes triseriatus and Aedes hendersoni were more cold hardy than larvae of Orthopodomyia and Anopheles. Neither preconditioning to cold nor dormancy was necessary for survival at -15°C for 24 h. Females that had survived temperatures to -25°C as eggs showed no impairment of reproductive capability. -from Authors