Pre-winter larval activity and feeding behavior of Erebia aethiops and E. cassioides in Austrian Alps

Abstract

Freshly hatched larvae represent critical but little studied phase in insect development. In butterflies inhabiting seasonally harsh environments, such as mountains of temperate regions, the larvae have only short time available for feeding before entering diapause. In the species rich genus Erebia, post-diapause larvae activate and feed exclusively in evening and late night hours, whereas the diurnal schedule and modifying effects of weather of pre-diapause larvae are practically unknown. Using captive observation with a transplant between alpine (2000 m) and mountain (800 m) altitudes, we studied larval activity of two species, alpine Erebia cassioides and lower-altitude E. aethiops, in Austrian Alps.Both species activated and fed both during day time and after the sunset, contrasting with the situation in post-diapause larvae. Both activity and feeding were strongly and species-specifically affected by temperature, cloudiness and humidity. Additionally, the loweraltitude E. aethiops, but not the alpine E. cassioides, restricted activity and feeding in the alpine altitude, indicating that some factors particular for alpine environments, possibly increased UV load or reduced air pressure, may limit the ability of this mountain species to develop above its vertical distribution limit.