LARVAL SURVIVAL IN POPULATIONS OF THE LARGE COPPER BUTTERFLY LYCAENA DISPAR BATAVUS

Lycaena dispar is recorded as an early case of extinction and subseque nt re-introduction in the UK. However, repeated establishment attempts have not resulted in self-sustaining populations, including tho:je ha ving taken place at Woodwalton Fen (Cambridgeshire, UK). Earlier studi es at Woodwalton Fen showed that the highest mortalities occurred betw een the egg stage and resumption of larval feeding in spring. This stu dy was designed; firstly, to investigate factors causing field mortali ty during different larval stages: secondly, to compare survival on Ru mex hydrolapathum foodplants in different habitat situations; and thir dly, to compare survival in a natural population (Weerribben, The Neth erlands) with the introduced Woodwalton Fen population. Experiments em ployed exclusion cages in order to examine the relative roles of verte brate and invertebrate natural enemies, and survival on foodplants in open fen and waterside situations was compared. Results suggest invert ebrate predation to be the dominant mortality factor acting upon pre-d iapause larvae. Over the winter diapause natural enemies do not have a significant role. However during both these stages losses still occur that are unaccounted for. Extensive winter flooding appears to increa se overwintering losses. Vertebrate predators cause significant mortal ity of post-diapause larvae. No significant difference was found betwe en larval survival on open fen versus water side plants. Comparison of introduced and native populations reveal that overwintering survival was significantly higher in the latter; potential reasons for this: di fference are discussed.