Sexual size dimorphism (SSD) is widespread among animals, but its developmental mechanisms are not fully undestood. We investigated the proximate causes of SSD in three male-larger and one monomorphic scarab beetles using detailed monitoring of growth in individual instars. Apart from the finding that SSD in all three male-larger species started to develop already in the first larval instar, we generally found a high variability in SSD formation among the species as well as among instars. Overall, sexual differences in developmental time, average growth rate, as well as in the shape of the growth trajectory seem to be the mechanisms responsible for SSD ontogeny in scarab beetles. In the third instar, when the larvae attain most of their mass, the males had a similar or even lower instantaneous growth rate than females and SSD largely developed as a consequence of a longer period of rapid growth in males even in cases when the sexes did not differ in the total duration of this instar. Our results demonstrate that a detailed approach, examining not only the average growth rate and developmental time, but also the shape of the growth trajectory, is necessary to elucidate the complex development of SSD.

Immature stages of I. pulverulenta (Olivier, 1789) (Coleoptera: Scarabaeidae: Cetoniinae: Incini) are described for the first time, and those of I. bonpalandi (Gyllenhal, 1827) and I. clathrata sommeri Westwood, 1845 are redescribed. A key to the third instar of Incini is presented, notes on Inca larval characters in the phylogenetic context of Cetoniinae and on scarab pupal morphology are also given.

Terrestrial snail shells can be considered partial resources for insects, and as such, the expansion of numerous snail species to anthropogenic habitats makes them increasingly available. Here, we address for the first time a complete profile of insects that use empty terrestrial snail shells during the winter period in Central Europe. The specialisation for shells made by certain snail species was uncommon; however, a number of species showed significant preferences for certain shell types. We found that the presence of empty snail shells in anthropogenic habitats drives the presence of many empty snail shell adopters in these habitats. Nevertheless, the increased availability of snail shells proved to be insufficient for a transition of all the species of snail shell adopters from natural to anthropogenic habitats. The avoidance of anthropogenic habitats among snail shell adopters was particularly distinct in species that use them only as a winter retreat but which require additional feeding and breeding resources, such as the true bugs. The availability of snail shells is thus a pre‐requisite of the presence of specialised snail shell adopters but is not necessarily sufficient to establish their presence in the respective habitat.

No abstract