Odour and colour similarity in two species of gregarious carabid beetles (Coleoptera) from the Crati Valley, southern Italy: A case of Müllerian mimicry?

Bombardier beetles of the genus Brachinus (Carabidae) are disagreeable prey because they discharge irritating quinones. Brachinus beetles live in aggregations and display warning colours. Like Brachinus beetles, Anchomenus dorsalis beetles produce methylsalicylate, and present a similar colour pattern. Anchomenus dorsalis beetles are usually found within Brachinus aggregations. Our aim was to investigate the similarity of cuticular chemical profiles of these two species to test the hypothesis of interspecific chemical mimicry. We investigated the cuticular composition of A. dorsalis, B. sclopeta, and Poecilus cupreus. Poecilus cupreas, a non-aposematic carabid commonly found in Brachinus spp and Anchonemus dorsalis aggregations, was used as a control. The cuticular profiles of the three species include 48 different hydrocarbons. The cuticular hydrocarbon profiles of the three species of carabids were different, but individuals of Brachinus were chemically more similar to those of Anchomenus than to those of Poecilus; in turn, individuals of Poecilus were more similar to Anchomenus than to Brachinus. We suggest that A. dorsalis is possibly mimicking the cuticular profile of B. sclopeta as an effective antipredator strategy. Brachinus sclopeta may benefit from a reduction of individual predation risk due to an increased number of aggregated preys (dilution effect), while A. dorsalis may increase the benefit both from the dilution effect and from the greater chemical defense of B. sclopeta.