Freezing susceptibility and freezing tolerance in Palaearctic Cetoniidae (Coleoptera)

Insects have evolved various adaptations that allow them to survive adverse seasons. In terms of cold-hardiness, they may classically be divided into freezing-susceptible versus freezing-tolerant species. But this concept of two alternative cold-hardiness strategies is now amendable, and to better u nderstand these adaptive mechanisms, it is of interest to study freezing re sistance in taxonomically related insect species, i.e., belonging to the sa me family or to a group of closely related organisms sharing similar resour ces. Freezing susceptibility and freezing tolerance have previously been re corded in the larvae of species in the same guild of the family Cetoniidae, which mainly colonise wood mould in hollow trees. We compared freezing har diness in five species of Cetoniidae, three species in the subfamily Trichi inae, Gnorimus nobilis (Linne), Trichius fasciatus (Linne), and Osmoderma e remita (Scopoli), and two species in the subfamily Cetoniinae, Cetonia aura ta (Linne) and Cetonischema aeruginosa (Drury). Our results mainly show tha t two contrasting mechanisms are used during winter by third-instar larvae: those of the Trichiinae (apart from O. eremita) are probably characterized by year-round freezing susceptibility, and those of O. eremita and the are probably distinguished by seasonal freezing susceptibility (summer) and se asonal freezing tolerance Cetoniinae are probably distinguished by seasonal freezing susceptibility (summer) and seasonal freezing tolerance (winter). We question the current taxonomic position of the genus Osmoderma. Morphol ogical, ecological, and behavioural arguments may be put forward to support the transfer of O. eremita from the Trichiinae to the Cetoniinae, and we s tress that ecophysiological arguments, often neglected in this kind of taxo nomic revision, must also be taken into account.