Species composition of blow flies (Diptera: Calliphoridae) colonizing pig carcasses exposed to bifenthrin‐ and clothianidin‐containing products

In forensic entomology, species identification is essential for determining the time of colonization (TOC)-the point at which insects first arrive and begin oviposition on remains. The TOC serves as a proxy for estimating a minimum postmortem interval (minPMI). This study examined factors associated with colonization (e.g., number of individuals, species present and adult emergence rates) of small pig carcasses (Sus scrofa L.). A total of 24 carcasses were placed in an open field and treated with low, medium or high concentrations of either bifenthrin- or clothianidin-containing products. In the bifenthrin trial, a negative correlation was observed between insecticide concentration and the number of flies reared, with abundance decreasing as concentration increased; however, this effect was not statistically significant (p = 0.11). In contrast, clothianidin exposure significantly influenced blow fly abundance (p = 0.05), with no colonization occurring at the highest clothianidin concentration. Analysis of adult fly emergence rates showed no significant effect from bifenthrin (p = 0.79) or clothianidin (p = 0.63). The species reared differed between trials. During the bifenthrin experiment, four blow fly species were identified-Phormia regina (Meigen), Lucilia illustris (Meigen), Lucilia coeruleiviridis (Macquart) and Lucilia sericata (Meigen). In contrast, only L. sericata and L. coeruleiviridis were recovered from the clothianidin trial. Additionally, dead Onthophagus hecate (Panzer) beetles (Scarabaeidae) and L. coeruleiviridis adults were observed on or near carcasses exposed to the highest clothianidin concentration. These findings contribute to the understanding of insecticide effects on the blow fly species colonizing remains. Furthermore, it holds forensic significance in cases where insecticide exposure, whether accidental or intentional, is suspected and could influence minPMI estimations during legal investigations.