Predicting the visitation of carcasses by carrion-related insects under different rates of degree-day accumulation

Common assumptions in forensic entomology are that insects visit and colonize carcasses following a predictable sequence, and that this succession varies among seasons. However, currently available evidence for insect succession on decomposing bodies is essentially descriptive and, to our knowledge, the fine-scale predictability of insect succession with respect to seasons has never been confirmed statistically. In this study, we test these assumptions through the sampling of carrion-related insects attracted to pig carcasses. The study was carried out during the summer and fall of 2006 in rural fields of New Brunswick, Canada. Of the five species of carrion-related insects with high enough occurrence on carcasses to allow modelling, three showed predictable occurrence with respect to degree-day accumulation and seasonal effects. This demonstrates that the occurrence probability of some carrion-related insects on carcasses can be estimated from meteorological records even across seasons with different rates of degree-day accumulation. As opposed to the prevailing idea that adult insects are not reliable for post-mortem interval estimation, the adults of some species exhibited a specific pattern of visitation that could be determined and used in forensic investigations. It is stressed, however, that the statistical predictability of species occurrence must be assessed before any species is considered as a post-mortem interval indicator.