Oviposition site selection by Coenagrion mercuriale (Odonata: Coenagrionidae)

Abstract

The aim of the study was to determine oviposition site selection in the endangered damselfly Coenagrion mercuriale in its UK stronghold and to determine hatching success of eggs. This was achieved by watching the behaviour of marked pairs from the onset of copulation to the end of oviposition and recording the number and duration of oviposition attempts and the plants oviposited in during the pairing. Pairs were either freely observed along a stream or placed in pre-placed cages within the stream. Stems into which oviposition had been observed were collected after four weeks and the fate of deposited eggs was determined. Pairs typically oviposited in several stems during multiple oviposition bouts, but usually in just one plant species. Mean total duration of oviposition behaviour was 671 s but ranged from 244 to 1,471 s. Mean number of eggs laid was 91 and ranged from 23 to 337. The female submerged completely in 15% of ovipositions. Mean egg deposition rate was 14 eggs per min but there was considerable variation. There was a significant positive relationship between total duration of oviposition in a stem and number of eggs laid in that stem. None of the habitat variables measured was a good predictor of duration of oviposition or number of eggs laid. Mean mortality of eggs was 14% at the time of collection and there was asynchronous development. Hypericum elodes was used significantly more than expected from its frequency in the environment and Eleocharis palustris, Molinia caerulea and Myrica gale significantly less.

Keywords: Odonata, dragonfly, Coenagrion mercuriale, egg hatching success, habitat selection, oviposition site

Issue section: Article