Ex Situ Breeding and Conservation of Osmoderma Species: A Systematic Review and Evidence-Based Breeding Guidelines for Reintroduction

Hermit beetles (<i>Osmoderma</i> spp.) are protected and endangered across Europe, experiencing ongoing decline throughout most of their range. Because nearly all populations are small and isolated, <i>Osmoderma</i> genus is highly susceptible to extinction and requires active conservation measures. The primary cause of decline in the genus is habitat loss, particularly the removal of hollow trees that provide essential larval habitat. The nutritional wood mold within these hollows, on which larvae depend for 3-4 years of development, is directly linked to population survival. The aim of this study was to develop methodical ex situ breeding guidelines for reintroduction designed to eliminate environmental constraints and ecological requirement gaps. We first synthesize literature-based evidence on habitat conditions, applied methods, study durations, and key ecological insights relevant to <i>Osmoderma</i> conservation. Based on these results, we then create an ex situ breeding guideline for reintroduction, combining published data with practical breeding objectives in cases where empirical data are limited.