Malathion and metformin in forensic entomotoxicology: a narrative review on impacts on necrophagous fly development and key research gaps

Forensic entomology provides critical estimates of minimum post-mortem interval (PMI) by analyzing necrophagous flies; however, substances like malathion (an organophosphorus insecticide) can disrupt insect development, compromising minimum PMI accuracy. Moreover, the disruption of blow flies’ development by metformin (a common antihyperglycemic drug) chronic exposure (lifelong) remains unknown, despite its potential to alter energy metabolism in Fall webworm moth, Hyphantria cunea (Drury, 1773) (Lepidoptera: Erebidae). Hence, this review examines the effects of malathion and metformin on necrophagous flies and identifies relevant gaps in entomotoxicological research. Malathion, frequently encountered in suicides and occupational exposures, inhibits acetylcholinesterase. This inhibition delays oviposition and extends larval development in necrophagous flies e.g. Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae). Despite these effects, the underlying biochemical and histological mechanisms for the developmental variations remain poorly understood. Nevertheless, the influence of malathion metabolites (iso-malathion and malaoxon) on the growth of necrophagous flies is inadequately studied. The co-occurrence of malathion and metformin in death cases is likely, yet research on metformin’s presence in necrophagous flies or its potential synergistic effects with malathion is notably absent. These significant knowledge gaps cloud the reliability of entomological evidence. In addition, while analytical techniques (e.g. gas chromatography-mass spectrometry) have enabled malathion detection in insect tissues, supporting cause-of-death determination, the same for metformin remains unreported. Hence, future research must prioritize elucidating the biochemical and histological mechanisms of these two compounds while developing eco-friendly analytical methods, such as those using deep eutectic solvents, to improve minimum PMI estimation and forensic integrity. • Malathion exposure delays development of forensically important necrophagous flies. • The effect of metformin on necrophagous fly development remains completely unknown. • Potential synergistic effects between malathion and metformin are entirely unstudied. • Biochemical mechanisms behind xenobiotic-induced developmental delays are unclear. • The influence of malathion’s toxic metabolites on fly growth is poorly understood. • Deep eutectic solvents are proposed for greener entomotoxicological analysis.