The impact of burnt carcass on the occurrence probability of Chrysomya albiceps and Lucilia ochricornis (Diptera: Calliphoridae) in southern Rio Grande do Sul, Brazil

Abstract

We evaluated the impact of burnt carcasses on the probability of finding Chrysomya albiceps (Wiedemann, 1819) and Lucilia ochricornis (Wiedemann, 1830) (Diptera: Calliphoridae), and the time it took for them to arrive at the experimental carcasss. These species are biological indicators of the postmortem interval (PMI) in forensic scenarios. Using stillborn pig carcasses, this study analysed how different degrees of burning affect the level of attraction and colonisation by these species. Experimental models were subjected to level 2 (CG2) and 4 (CG4) burning according to the Crow-Glassman (CG) scale, ranging from fresh to skeletonization. Generalised Linear Models (GLM) with a Binomial distribution were used to evaluate the influence of decomposition time and experimental treatment on the probability of occurrence of each species. Additionally, survival analyses with the Weibull distribution were used to investigate how long it takes until the arrival of the first fly species in each experimental group. The results indicate that burning affects the probability of occurrence and colonisation time of the studied fly species. Although both species were affected by high degrees of burning, Lucilia ochricornis was more heavily affected than Chrysomya albiceps. This pattern was reflected in the time it took for the first occurrence of each fly species. In both cases, it took longer for flies to arrive at carcasses that had been more severely burnt. In the case of C. albiceps, the longest mean time until a fly was detected (Weibull, α = 79.9 h) happened in the CG4 group, followed by the CG2 group (α = 65.6 h) and the control group (α = 51.5 h). In contrast, for L. ochricornis, the longest mean first occurrence time (α = 85.4 h) was in CG2 group, followed by the Control (α = 49.1 h) and CG4 (α = 54.4 h) groups. This study emphasises the importance of considering whether or not a carcass was burnt and its degree of burning in forensic investigations, given that this variable can influence the accuracy of PMI estimation in crime scenes.