The required day number and timely induction of diapause in geographic strains of the mosquito Aedes atropalpus

Abstract

Diapause is triggered in A. atropalpus from 14°N lat when 9 or more short-day photoperiod cycles occur during the photosensitive 4th instar and pupa. Temperatures of 22°C and higher cause part or all of this population to complete the photosensitive period in less than 9 days thereby avoiding diapause. In contrast, 4 short-day cycles during the photosensitive period are sufficient to trigger diapause in A. atropalpus from 45°N lat. This population experiences the 4 required days at temperatures as high as 28°C. A strain from an intermediate location of 34°N lat must “see” 7 short days during the photosensitive stages for induction of diapause. This requirement is met at temperatures of 24°C and less. These results suggest that southern strains of A. atropalpus have evolved a means of avoiding short-day induced diapause if temperatures are high and other requirements for growth are available. A correlation between critical daylength for induction of diapause and geographic origin has been shown for several insect species. The evolution of a requirement for different numbers of diel cycles during the photosensitive period is another means of modifying the diapause response in populations from different latitudes and geographic areas.