An Adult Population Study of Pyrrhosoma nymphula (Sulzer): (Odonata: Coenagrionidae)

Abstract

A localized population was studied by marking and recapturing specimens during the flying season. Emergence was restricted in time and showed a diurnal rhythm with a peak period between 9.00 and 10.00 a.m. B.S.T. Unfavorable weather conditions postponed emergence until the following day. Shelter and warmth appear to be major factors influencing the choice of supports by transforming larvae. The period of mature adult flight lasted from May 30 until July 19, but an active population at the pond existed only to July 1. Insects returned to the pond as mature adults about 15 days after emergence. An avg. daily survival rate of 85% gave the best fit with recapture data for the whole flying season. This involved a daily elimination rate of about 15% and an avg. expectation of life of 6.7 days. Numbers at the pond fell rapidly after arrival of an emergence group, new arrivals tending to replace previous residents. The adult population was fairly homogeneous with respect to the age of its members. It is suggested that spp. entering the final larval instar in autumn may be expected to have a mass emergence in spring.