Photoperiodic control of development in the pitcher-plant mosquito, Wyeomyia smithii

Abstract

Wyeomyia smithii diapause in the third larval instar. Long days avert or terminate and short days promote or maintain diapause. Diapause occurs early in the third instar and may be terminated by photoperiodic stimuli without the intervention of chilling or other factors. Fifty percent termination of diapause requires about 3 long days and another [Formula: see text] days are consumed in the third instar for postdiapause development. The critical daylength is identical for both the initiation and termination of diapause, 14.75 h of light per day. But, the photoperiodic clock monitoring diapause decisions is several times as accurate during initiation as in termination, reflecting the more drastic environmental consequences of development misdirection in the fall than in the spring. This accuracy is further enhanced by a prolongation of the second instar under short-day conditions. The doubling in the duration of the second instar exhibits the same critical daylength properties as diapause determination.The third instar is divisible into four distinct developmental periods: prediapause, diapause, termination of diapause, and postdiapause. Methods for quantifying these periods are presented. Similar manipulations could be employed for other diapausing arthropods, regardless of the stage at which dormancy occurs or the cues used in its regulation.