Density-dependent changes in sex ratio in Colias lesbia (Lepidoptera: Pieridae)

Abstract.

• 1 The changes in sex ratio of a population of Colias lesbia were studied for four consecutive years.
• 2 A constant sex ratio was found in the samples taken in the 34 days following the last harvest of the alfalfa.
• 3 For the samples taken 35 or more days after the harvest the sex ratio decreases as the total number of adults caught increases.
• 4 The indirect evidence collected suggests that differences in emigration tendencies between sexes play a major role in determining the sex ratio in this species.