Beetles “in red”: are the endangered flat bark beetles Cucujus cinnaberinus and C. haematodes chemically protected? (Coleoptera: Cucujidae)

Abstract

Two native species of the genus Cucujus show a wide geographic distribution in Europe, Cucujus cinnaberinus (Scopoli, 1763) and C. haematodes Erichson, 1845. Although data on the distribution and ecology of these rare and endangered species are increasing, there are few reports on their biology and behaviour, and some aspects of their feeding ecology remain problematic. Our aim was to study, for the first time, the cuticular chemical profiles of these two beetles to (i) investigate the presence of chemicals potentially involved in defence by pathogens and (ii) lay the foundation for understanding the role of their bright red colour. The analysis of the cuticular profile was performed in-vivo by solid phase microextraction coupled with gas chromatography-mass spectrometry. In the cuticular profiles of the two species we identified 24 compounds belonging to different classes of molecules, i.e. hydrocarbons, aldehydes, esters, n-alkyl morpholines, and a high number of organic acids. Qualitative differences in terms of both signal intensity and detected compounds were found between the two species. As reported in other insects, the remarkable array of avoidance substances suggests a strict relationship with the bright red colour of the adults, which probably acts as an aposematic or warning signal. European Cucujus species are probably well protected against enemies because some identified chemicals, particularly fatty acids, are related to an antipredatory strategy to fight off predators that use their sense of smell to locate their prey. Other substances found on the cuticular layer of these beetles are probably involved in an antimicrobial and antifungal function, as demonstrated in other insects living in habitats that host many pathogens.

From Phenology and Habitat Preferences to Climate Change: Importance of Citizen Science in Studying Insect Ecology in the Continental Scale with American Red Flat Bark Beetle, Cucujus clavipes, as a Model Species

“…In the literature, one can find that all stages of Cucujus clavipes are recorded under the bark of different coniferous and deciduous tree species [ 88 , 94 , 150 , 151 ] but with no details about diameter and length of dead tree. At least some of those factors, which are recognized as very important in other Cucujus species, e.g., [ 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 , 160 ], possibly can be crucial also in case of C. clavipes .…”

Niche partitioning among dead wood-dependent beetles

“…Therefore, one indication of niche partitioning is that one species mainly avoids the others even if all these species have highly similar dietary preferences 17 . Another possible explanation for the low niche partitioning among species is that the most abundant species, C. cinnaberinus , displays many signs of antipredator strategies, together with antimicrobial and antifungal functions 40 . The same adaptations could also be expected for the pyrochroids 41 – 43 .…”

Artificial Feeding and Laboratory Rearing of Endangered Saproxylic Beetles as a Tool for Insect Conservation

“…Before the experiments, the larvae were fed once a week exclusively with minced meat, considered suitable as food for laboratory rearing based on a previous study ( Bonacci et al 2018 ). A total of 120 larvae and a total of 48 emerged adults ( C. cinnaberinus = 24 and C. haematodes = 24) were used for experiments on dietary preferences.…”

“…1 ) and Fagus sylvatica L. 1753 (Magnoliopsida: Fagaceae) ( Anderson and Nilssen 1978 , Bonacci et al 2012 ). Flat bodies of larvae and adults are well adapted for the narrow subcortical environment of dead trees ( Bonacci et al 2018 ). Larvae hide under the bark and the emerged adults spend most of their life on the trunks or logs and inside bark crevices where they feed and reproduce ( Straka 2017 ).…”