ELSEVIER PII: S0006-3207(97)00006-2 Biological Conservation 82 (1997) 61~56 © 1997 Published by Elsevier Science Ltd All rights reserved. Printed in Great Britain 0006-3207/97 $17.00 + 0.00 THE EFFECTS OF FLOODING ON THE SURVIVAL AND BEHAVIOUR OF OVERWINTERING LARGE HEATH BUTTERFLY Coenonympha tullia LARVAE J. Joy & A. S. Pullin Department of Biological Sciences, Keele University, Staffordshire ST5 5BG, UK (Received 13 May 1996; accepted 21 November 1996) Abstract The rehabilitation of raised mires commonly requires water levels to be raised in order to reinstate Sphagnum- based raised mire vegetation over peatland areas which have previously been extensively worked by commercial peat cutters. Coenonympha tullia larvae living on cotton- sedge tussocks Eriophorum vaginatum in the base of peat cuttings will be inundated by the rising water levels under such management regimes. The submergence of overwin- tering C. tullia larvae was found to have a marked impact on their long term survival. The numbers of larvae that survived to resume feeding the following spring was lower for all submergence times (3 to 108 days) compared with controls; no larvae survived a submergence period of 108 days. Total submergence had two effects. First, it caused an immediate increase in mortality after 7 days (with larval death occurring under water) and second, a longer term increase in mortality over the next few months. Behavioural tests suggested that C. tullia larvae usually respond to the raising of water levels by trying to climb out of the water. Results suggest that, on sites where the conservation of C. tullia is important, water levels should not be raised so high as to totally submerge E. vaginatum foodplants containing C. tullia larvae until E. vaginatum has spread sufficiently on the higher peat surface to pro- vide a replacement habitat. © 1997 Published by Elsevier Science Ltd Keywords: lepidoptera, larvae, submergence, peatland restoration. INTRODUCTION The large heath butterfly Coenonympha tullia is an inhabitant of wet bogs and mosses. It has a widespread but local distribution in northern Europe with numer- ous local extinctions in northern England, Wales and Correspondence to: Dr A. S. Pullin, School of Biological Sci- ences, The University of Birmingham, Edgbaston, Birming- ham, BI5 2TT, UK. 61 Ireland occurring due to the reclamation of bog for agricultural purposes, for forestry or for road building (Thomas, 1989; Emmet & Heath, 1990). The flight per- iod is usually from late June until August although some colonies at high altitudes do emerge later (Thomas & Lewington, 1991). Eggs hatch around 14 days after they are laid and larvae then feed on the tips of cotton- sedge Eriophorum vaginatum until September. Third instar C. tullia larvae have always been thought to hibernate deep within the tussocks of their foodplant where it is assumed that they can withstand long periods of flooding (Melling, 1987; Emmet & Heath, 1990; Thomas & Lewington, 1991). The Fenn's and Whixall Mosses complex in Shrop- shire and Clwyd is a particularly important site for C. tullia as the butterfly is on the southernmost edge of its English range and occurs as subspecies davus. An unu- sual variant has frequently been recorded here (Russ- wurrn, 1978; Joy, 1991), which is usually referred to as ab. cockaynei. As the management programme currently being carried out here by English Nature and the Countryside Council for Wales is one of the first attempts in this country to restore raised mire vegeta- tion on a site which has been extensively drained by commercial peat cutters, it may well be that, in future, its management is held up as a national example of how other similar sites should be managed. The drain blocking programme has resulted in many C. tullia breeding areas being subjected to winter flooding for long periods of time. This has raised concerns that these high water levels might be having a deleterious effect on the C. tullia population. Flooding is already known to influence the survival rates of several wetland insects including the large copper butterfly Lycaena dispar (Purefoy, 1929; Duffey, 1968, 1977; Tinning, 1975; Pullin et al., 1995; Webb, 1995), the larch sawfly Pristi- phora erichsonii (Lejeune, 1947; Lejeune & Filuk, 1947; Lejeune et al., 1955) and the rare caddisfly Hagenella clathrata (Berry et al., 1996). In this study, experiments were carried out to assess (1) the impact of flooding on overwintering C. tullia larvae in terms of their long term survival and (2) their behavioural responses to flooding.