Timing of eclosion affects diapause development, fat body consumption and longevity in Osmia lignaria, a univoltine, adult-wintering solitary bee

Most Insects from temperate areas enter diapause ahead of winter Species diapausing in a feeding stage and accumulating metabolic reserves during permissive pre-wintering conditions are expected to enter diapause shortly before the onset of winter In contrast species diapausing in a non-feeding stage are expected to lower their metabolism as soon as possible to avoid excessive consumption of metabolic reserves The solitary bee Osmia lignaria winters as a non-feeding adult within its cocoon but previous studies show important weight losses and increased winter mortality in populations pre-wintered for extended periods We measured respiration rates to assess diapause initiation and maintenance during pre-wintering and tested whether timing of adult eclosion affected fitness by measuring fat body depletion winter mortality and post-winter longevity We worked with different cohorts of a population reared under natural conditions and manipulated pre-wintering duration in a population reared under artificial conditions In agreement with our expectation O lignaria lower their metabolic rates within a few days of adult eclosion but nonetheless suffer strong weight loss during pre-wintering Early developing individuals suffer greater weight loss and fat body depletion and have short post-winter longevity Although we found no differences in winter mortality among treatments our results indicate that Increased mortality may occur in years with late winter arrivals We discuss fundamental ecophysiological differences between adult and prepupal diapause within the Megachilidae and hypothesize that species wintering as adults will be more negatively affected by a situation of extended summers under a scenario of global warming Published by Elsevier Ltd