Induction of diapause in female mosquitoes, Culiseta inornata by a decrease in daylength

Abstract

Female Culiseta inornata that had been transferred from 16 hours daylength at 20°C (16 hr, 20°C) to 12 hr, 10°C shortly after ecdysis to the fourth larval instar, or shortly after larval-pupal ecdysis, developed their ovarian follicles to a size and stage characteristic of diapause. Females reared and maintained at constant 16 hr, 20°C or at 12 hr, 10°C, or transferred shortly after pupal-adult ecdysis, developed significantly larger follicles characteristic of gonoactivity. In a second experiment, females were reared at 16 hr, 20°C until larval-pupal ecdysis, then transferred to a 16 hr or 12 hr daylength at 10, 15, or 20°C. At 14 to 15 days after adult emergence, follicles of the females at 12 hr daylength were as small as those of diapausing females, and signiticantly smaller ( P < 0.01) than those of females at 16 hr daylength. The proportion of females 7 to 8 days after emergence that fed on a man, and the proportion of blood-fed females that matured eggs, increased both with daylength and with temperature, the lowest rates being seen in females at 12 hr, 10°C (20% fed and none matured eggs) and the highest in females at 16 hr, 15°C (72% fed and 96% matured eggs). The proportions of blood-feds at 12 hr, 15°C and at 12 hr, 20°C that matured eggs were higher than predicted from their follicle development. Four of 191 females over 12 days after emergence in the two experiments (2.1%) were autogenous.