Experimental effects of paracetamol overdose on the development of forensic insects.

In forensic entomology, postmortem interval (PMI) estimation relies on the age, development, and succession patterns of insects on decomposing remains; however, the presence of drugs in the body can disrupt insect development and compromise the accuracy of these estimates. Paracetamol, a commonly used over-the-counter drug in Southern Africa, is often implicated in both intentional and accidental overdose cases. This study investigates the effects of paracetamol on insect development using spiked pig carcasses as experimental models to simulate human overdose. Three pigs received paracetamol at ascending doses 75 mg/kg (toxic), 150 mg/kg (lethal), and 300 mg/kg (double lethal), and the fourth pig served as an untreated control. The experimental carcasses were placed in separate metal cages in a natural outdoor environment during the autumn season, and insect samples were collected daily over a 32-day period. Observations and morphological measurements of the length, width, and weight were recorded for selected dipteran and coleopteran species of forensic value. Results showed that Chrysomya putoria and Chrysomya megacephala exhibited an increased larval length, width, and weight at double lethal doses. Lucilia sericata showed significant reductions in weight at all paracetamol doses (p = 0.012, 0.001 and 0.001) in comparison to the control, while Chrysomya albiceps and Thanatophilus micans were not affected by the drug. Furthermore, results showed that the mortality rates of newly emerged Ch. putoria, Ch. megacephala, Ch. albiceps and L. sericata were higher in paracetamol-treated groups compared to those observed from the control group, with the rates of 22.2% at the toxic dose, 35.0% at the lethal dose, 45.0% at the double lethal dose, and 11.1% in the control group. Morphological abnormalities were observed in newly emerged adults of Ch. putoria and L. sericata that showed progressive wing deformities at the toxic and lethal doses and discoloration at the double lethal dose. Ch. albiceps exhibited no observable deformities across all doses. These findings show that paracetamol disrupts critical developmental processes in certain species in a dose-dependent manner, highlighting the need to study its effects on other forensically important insects. Moreover, these findings contribute towards enhancing PMI precision and advancing forensic entomotoxicology in the region by generating local baseline data for KwaZulu Natal province, South Africa.