Effect of carcass model on maggot distribution and thermal generation of two forensically important blowfly species, Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart)

摘要

At feeding stage, blowfly larvae (Diptera: Calliphoridae) form aggregation to facilitate the breakdown of a human body after death. The aggregation structure of blowfly larvae could probably be different depending on fly species and food size. In forensic investigations, corpse size does not only affect the internal temperature after death, but it could also potentially influence the distribution, aggregation temperature, and species of flies that inhabit a corpse. However, there is no reference available to explain how these factors could affect maggot distribution pattern and thermal generation. The best way to answer this is by accessing blowfly aggregation on multiple forensic entomology animal models of different sizes. Thus, this research is a preliminary assessment to determine maggot aggregation structure and its thermal generation in three carcass species which are commonly used as a surrogate for human corpses in Malaysia. Frequency of Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart) aggregations at a different location in carcass was determined. Aggregation temperature, depth, perimeter, area, and volume of tightly packed aggregations were measured. These variables were compared to ambient temperature and relative humidity. Correlation analysis was performed to access any relationship between each variable. Aggregation temperature was found strongly correlated to carcass temperature (r = 0.65, p  0.05), moderately correlated to carcass ground temperature (r = 0.57, p  0.05), and weakly correlated to aggregation depth (r = 0.21, p  0.05), relative humidity (r = 0.06, p = 0.35), and ambient temperature (r = 0.01, p = 0.89). The rate of carcass loss was significantly influenced by carcass model (p  0.05). The frequency of Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae) aggregation was more in rat carcasses, while for rabbits and macaques, Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) was more frequent. Aggregations of Chrysomya rufifacies were frequently observed located below carcasses while Chrysomya megacephala were observed mostly in the mouth and genitalia. Chrysomya rufifacies aggregations have produced higher temperature compared to Chrysomya megacephala. Carcass model was proven to be a critical  factor in larval aggregation distribution and temperature. Therefore, this preliminary study has pointed out the necessity of proper selection of animal model for forensic entomology study. Food source characteristics, particularly body size, could play a significant factor in larval aggregation distribution and thermal generation, therefore making this factor important when making postmortem interval (PMI) estimation based on larval growth.