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 anti-predatory 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.
Highlights
The flat bark beetles of the genus Cucujus are an example of extreme adaptation to the under-bark microhabitat
Their extremely flat bodies allow them to crawl through the thin space that opens between the xylem and phloem of decaying dead trees
The beetle was thought to be extinct in Italy after 1960, in the last decade it has been found in Piedmont and on the Alburni mountains in the Campania Region, by Biscaccianti et al (2009), and, after 49 years of absence, in the Sila National Park in Calabria (Mazzei et al 2011)
Summary
The flat bark beetles of the genus Cucujus are an example of extreme adaptation to the under-bark microhabitat. Their extremely flat bodies allow them to crawl through the thin space that opens between the xylem and phloem of decaying dead trees. The European species C. cinnaberinus (Scopoli, 1763) is strictly protected and enclosed in Annexes II and IV of the EU Habitats Directive 92/43, with the aim of maintaining existing populations. It has been classified as “near threatened” in Europe by the International Union for Conservation of Nature (IUCN) organisation and “vulnerable” in Italy (Carpaneto et al 2015). In Southern Italy, they provide a simple and Cuticular profiles in adults Cucujus cinnaberinus and C. haematodes 129 useful tool for periodic diversity monitoring in forest nature reserve networks (Mazzei et al 2018)
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