Cold hardiness of some adult mosquitoes in central Alberta

Abstract

Temperatures were recorded continuously in overwintering sites of female Anopheles earlei Vargas, Culex territans Walker, and Culiseta alaskaensis (Ludlow) near George Lake (53°57′N, 114°06′W). Daily mean and absolute minimum temperatures in winter (November–March) 1972–75 were −6 and −31 °C in three rock piles, −6 and −21 °C in a log pile, −2 and −7 °C in a mammal burrow, and −10 and −42 °C in the open air. Live An. earlei and Cx. territans from rock piles in winter had mean supercooling points of −23.6 and −26.1 °C respectively. Freezing to determine supercooling points was fatal to all mosquitoes tested. Culex territans females collected in fall (September–October) had a mean supercooling point of −20.1 °C and an LT50 (median lethal time) of 138 days at −5 °C. Female Cs. inornata (Williston) were not found in winter; those collected in fall had a mean supercooling point of −11.3 °C and LT50 of 20 days at −5 °C. Supercooling points of Cs. inornata females laboratory reared at 20 °C were lowered after 1 or 10 days at 10 °C, but not at 2 °C, and not affected by blood or meconium in the midgut. Laboratory-reared, diapausing Cs. alaskaensis females had a mean supercooling point of −12.9 °C and an LT50 of 30 days at −5 °C. Nondiapausing Cs. inornata females had a mean supercooling point of −14.4 °C but their LT50 was only 9.3 days at −5 °C.