Variation in contact chemical cues may mediate differential predator response in the colour polymorphic tortoise beetle, Chelymorpha alternans

Differential predation on species with intraspecific colour variation has been explored in various systems and is often implicated as the driving force behind colour polymorphism maintenance. Here, investigation done on whether predation contributes to the maintenance of extensive colour variation in the Neotropical tortoise beetle, Chelymorpha alternans (Chrysomelidae). Recorded predation rates on different colour pattern phenotypes by three common, generalist invertebrate predators, and identified potential chemical signals of unpalatability. Predaceious mantids (Orthoptera, Mantidae) consumed no beetles, regardless of phenotype, whereas the giant orb-weaving spider (Trichonephila clavipes; Araneidae) consumed all three beetle phenotypes. The carton-nest ant, Azteca chartifex (Formicidae), displayed differential predation; the rufipennis phenotype of C. alternans was sometimes consumed, the metallic phenotype was never consumed, and the veraguensis phenotype was consumed in the first three encounters and subsequently discarded, suggesting a learned avoidance behaviour. Using gas chromatography–mass spectrometry, it was determined that cuticular hydrocarbon profiles were similar between the metallic and militaris-a phenotypes. The rufipennis phenotype showed pronounced differences and displayed the greatest among-individual variation in elytral cuticular profiles. Between-phenotype variation in chemical cues, and differences in how predators receive those cues, may mediate predator response, and play a role in maintaining colour variation in this species.