Ecological studies of Ischnura elegans (Vander Linden) (Zygoptera: Coenagrionidae). I. Age groups, emergence patterns and numbers

Imaginal populations of the damselfly Ischnura elegans were studied by means of capture-recapture methods in Cheshire and Pembrokeshire, U.K., from 1965-1970. Age grouping of both males and females was accomplished by noting characteristic colour changes associated with the ageing process. There is some indication that the distribution of immature imagines in the colonies at Dunham, Cheshire, was partly determined by the available vegetation shelter from wind. Acorus seems to afford greater protection than Juncus. By noting the age group composition of the colonies and studying the population estimates it was found that I. elegans had bimodal emergence curves with peaks in June and July/August. The population sizes at the Dunham Ponds bore a direct relationship to the size of the pond. The total estimated season’s sizes for Ponds 1 and 2 (1965) and Pond 3 (1966) were about 2000, 4700 and 450 respectively. The sexes were about equally represented in these estimates. The populations in June 1970 at Ponds 1 and 3 were between three and five times larger than for the corresponding months in 1965 (Pond 1) and 1966 (Pond 3). It was found that I. elegans is active under a wide range of weather conditions, only winds in excess of 20 knots, heavy rain, and a day temperature of less than 15°C (especially in combination) completely suppress flight.