Thermal polymorphism, usually represented by thermal melanism (darker coloration in cooler habitats), is a well-known phenomenon in animals. In Cetoniinae, several species in captivity tend to become darker after several generations of breeding, which is probably caused by a lower temperature than is typical for their native habitats. Pachnoda iskuulka is a beetle species occurring in Somaliland. This species is easy to breed in captivity, and it is colorful and variable in the proportions of yellow, red, and black coloration. We kept this species from the first instar larva to the adult stage at three different temperatures. Elytra and pronotum of the adults were photographed, and proportions of the three main colors were measured. The proportion of black coloration significantly increased with size and decreased with temperature, while the proportion of yellow color increased. This species is certainly thermally polymorphic, which can be an adaptation for activation even at lower temperatures. The possible mimicry with beetles of the genus Hycleus is discussed. It is the first confirmation of thermal polymorphism in Cetoniinae and one of a few in Coleoptera.

• Keywords
• beetle breeding, color ratio, coloration, habitat, mimicry, polymorphism,
• Publication type
• Journal Article MeSH

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.

• MeSH
• Biological Evolution * MeSH
• Coleoptera anatomy & histology   growth & development   MeSH
• Larva growth & development   physiology   MeSH
• Sex Characteristics * MeSH
• Body Size physiology   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH