Notes on biometric variability in invasive species: the case of Psacothea hilaris hilaris

Species morphometric variability is the result of the combined effect of genes and environment. This is emphasized in insects, especially in ones that rely on discrete food resources, such as xylophagous insects. Psacothea hilaris hilaris (Pascoe) (Coleoptera Cerambycidae Lamiinae), an exotic beetle already established in Italy, is used as a model species for the study. The findings presented in this research increase knowledge of morphological and colourimetric traits in P. h. hilaris and support the hypothesis that environmental cues can impact certain important morphometric features of exotic insects. Principal component analysis (PCA) and Bayesian’s posterior probability applied to the dimensions of specimens collected over a four-year period showed that some morphological parameters changed significantly over the years. According to PCA the most meaningful morphometric variables were body length, elytral length, and antenna-to-body length ratio. One of the most significant results is the variability of the antenna-to-body length ratio over the period of the study. In cerambycids longer antennae allow for better detection of host tree, oviposition site, and favour mating strategies. Consequently variability in this physical trait can influence the ability of the species to adapt to a new habitat.