Fall Decay Deceleration in Northern Latitudes: Merely a Matter of Cold?

The decomposition of cadavers and large vertebrate carcasses is the result of complex processes primarily influenced by ambient temperatures. Thus, low temperatures can alter decomposition by curtailing tissue autolysis and bacterial decomposition, and by limiting insect activity contributing to necromass removal. In this study, we tested whether carcass decomposition rate is modulated not only directly by temperature and insect occurrence, but also indirectly by the mediation of interactions among insects by ambient temperature. To test this, a comparative analysis of the decomposition of domestic pig carcasses in summer and fall was conducted in Atlantic Canada. The results indicated that carcass decomposition standardized to account for seasonal differences was significantly decelerated in the fall as opposed to the summer during the later decomposition stages and was sometimes incomplete. Moreover, the arrival, presence, and departure of insects from carcasses during ecological succession differed between summer and fall. Necrodes surinamensis (Fabricius) (Coleoptera: Silphidae) and Creophilus maxillosus (Linnaeus) (Coleoptera: Staphylinidae) maintained higher abundances late during succession in the fall than in the summer and their abundance was related to a decline in decomposition rates, probably because these species feed on dipteran larvae promoting necromass removal. These results demonstrate the variability in response to environmental parameters of insects of forensic importance and support the idea that slowed decomposition in the fall may be exacerbated by changes in interspecific interactions among insects. Furthermore, these results suggest that successional studies of insects carried out in the summer have little forensic utility for cadavers found in cold weather conditions.

Small Bait Traps May Not Accurately Reflect the Composition of Necrophagous Diptera Associated to Remains.

Small bait traps are beginning to emerge in forensic entomology as a new approach to sample early-colonizing necrophagous Diptera species while reducing the investment in time and energy in obtaining information. To test the hypothesis conveyed by the literature that these traps can be a substitute for whole carcasses, we simultaneously documented the Diptera assemblages visiting and colonizing domestic pig carcasses and small traps baited with pork liver. Results indicated that Diptera species occurrence and assemblage composition in the small bait traps and on the carcasses differed, while they were similar when comparing only the pig carcasses. These results are in agreement with the literature that examined insect colonization of other decaying substrates. Although small bait traps can be useful tools to document the communities of necrophagous Diptera in a given area, we stress that caution must be exercised when extending the data obtained by these traps to courtroom proceedings.

Is Forensic Entomology Lost in Space?

Spatial and scale effects have barely been considered in forensic entomology, despite their pervasive influence on most of the parameters affecting the development of insect larval stages and the progression of insect succession on cadavers. Here, we used smoothing/interpolation techniques and semivariograms to document the spatial dynamics of sarcosaprophageous Calliphoridae, an important forensic taxon, in the Greater Moncton area in New Brunswick, Canada. Results indicated that the spatial dynamics of Calliphoridae differed between species, some species showing strong patterns of regional aggregation while others did not. Multivariate spatial correlations indicated that interspecific relationships in space varied widely, ranging from local and large-scale aggregation to spatial anticorrelation between species. Overall, this study suggested that even within a restricted timescale, the spatial dynamics of Calliphoridae can operate at many scales, manifest in different patterns, and be attributed to multiple different causes. We stress that forensic entomology has much to benefit from the use of spatial analysis because many important forensic questions, both at the fundamental and practical levels, require a spatial solution.