The effect of sex and age on survivorship of adult damselflies in the laboratory (Zygoptera: Coenagrionidae)

Longevity in the laboratory was measured for 1071 individuals of Ischnura graellsii, 75 of I. pumilio, 127 of Coenagrion scitulum and 41 of Enallagma cyathigerum. Individuals were maintained in 5 insectaries (50x50x50 cm) with numerous perching substrates, and adults of Drosophila were added as food. Results indicate that males do not live as long as females, in all spp„ although the difference was not significant for C. scitulum. Most I. graellsii adults were obtained from the offspring of 33 laboratory crosses. In this sp. a 2-way ANOVA indicated significant effects of both family and sex on longevity, and family-sex interaction occurred in the F,. It is suggested that this sex difference in longevity is mainly due to the contrasting behaviour of the 2 sexes; males spent much time in prolonged flights looking for females, and great harassment occurred between them. This activity is likely to reduce the longevity. The longevity of 3 9 phenotypes of I. graellsii was similar. Although in all spp. mortality was rather age-independent, a maximum was recorded in the age-class of 4-5 days. This could be due to the failure of some individuals to capture the Drosophila, and could explain the low recapture rate of leneral individuals in the field. Marking had no effect on mortality. This suggests that the low recapture rate, observed in many field studies the day after marking, is probably due to greater dispersal rather than to mortality. The sequence of emergence of both sexes was random in all spp., and so was the sequence of female phenotypes in I. graellsii families. Mortality and deformation during emergence affected ca 11-13% of adults. The importance of insectaries for the study of adult damsclflics is discussed.