Regulation of damseifly populations: the effects of larval density on larval urvival, development rate and size in the field

SUMMARY. 1. The popuhttion density of Coenagrion pttella larvae was monitored in five populations, and of Ischntira elegans in two populations, between October 1982 and May 1983. 2. There was no measurable mortality of larvae over winter and no larval growth until April. Larvae in high density populations were smaller than those in low density populations and were more likely to have a semi‐ voltine life history. 3. The population density of C. ptiella was also monitored (more frequently) in two populations with differenl initial densities between July and November 1983. In the high density population there was a constant rate of larval mortality, while in the low density population there was no detectable larval mortality, indicating that larval mortality may be density dependent. Larvae in the high density population were again smaller, and more likely to be semi‐voitine, than those in the low density population. 4. The role of density dependent larval growth, development and mortality in the regulation of damseifly populations is discussed.