Impact of bifenthrin and clothianidin on blow fly (Diptera: Calliphoridae) oviposition patterns under laboratory and field conditions

Blow flies (Diptera: Calliphoridae) can detect decomposing remains and begin colonizing the resource through oviposition soon after. The estimated time between colonization and insect evidence collection is referred to as the time of colonization (TOC). Forensic entomologists use the TOC to help estimate the minimum postmortem interval (mPMI), or the time between death and the discovery of remains. The presence of insecticides can influence blow fly behaviors, including oviposition. This study aimed to investigate how different concentrations of two insecticides, bifenthrin and clothianidin, affected blow fly oviposition both under laboratory and field conditions. In the laboratory experiments, Lucilia sericata (Meigen) and Phormia regina (Meigen) blow flies were exposed to beef liver treated with varying concentrations of bifenthrin or clothianidin. In the field, stillborn pig carcasses were treated with the same concentrations and time to oviposition was assessed and oviposition site preference observed. Insecticides have the potential to deter insect activity. Therefore, we hypothesized that insecticide exposure would result in delayed oviposition, altered site preferences, and increased mortality due to their modes of action. Statistical analyses indicated that the insecticides had no significant effects on the time to oviposition in the laboratory experiments, although species- and insecticide-specific effects were observed. Clothianidin, however, significantly affected mortality rates in both species. During field trials, bifenthrin significantly delayed oviposition, while clothianidin inhibited oviposition at the high concentration. These findings offer valuable insights for improving entomological evidence analysis in criminal investigations where insecticide exposure is suspected.