INTRODUCTION

Leather et al. (1993) asked the pertinent question ‘What is overwintering?’ They answered themselves by quoting Mansingh (1971) who defines insect hibernation as ‘a physiological condition of growth retardation or arrest, primarily designed to overcome lower than optimum temperatures during winter or summer’. Mansingh (1971) subclassified insect hibernation into different categories depending on the insect's response to winter conditions. The three different categories are quiescence, oligopause and diapause representing, in sequence, increasingly highly evolved systems of dormancy. The common green lacewing (Chrysoperla carnea) s. lat. can be considered to enter diapause. After Leather et al. (1993) this is characterised by (1) a definite preparatory phase usually initiated by a temperature independent factor such as photoperiod; (2) absence of feeding by the insect during winter; and (3) the return of favourable conditions does not result in immediate termination of diapause – a complex series of events such as accumulation of heat units is required first.

Common green lacewings diapause in large clusters of adult insects. Observed overwintering sites include unheated parts of buildings, barns, the underside of tree bark, and leaf litter (Canard & Principi, 1984), with the choice of site partly determined by sibling species (Thierry et al., 1994). Normally, due to a combination of fluctuating temperature and predation, winter mortality is high (Sengonca & Frings, 1987). However lacewings will colonise artificial overwintering chambers especially designed for the purpose and in these overwinter survival can approach 100% (Sengonca & Henze, 1992).