Detection of pesticides in forensically important blow fly larvae

Few studies have been conducted on the effect of pesticides on postmortem interval (PMI) and the ability to detect pesticides in forensically important blow flies. The purpose of this study was two-fold: 1) to compare the delay in oviposition on pig carcasses treated with different pesticides and 2) to quantify the amount of pesticide in the larvae at each developmental stage. The pesticides were chosen because they are all readily available and come from different chemical classes: malathion, an organophosphate; carbaryl, a carbamate; and permethrin, a pyrethroid. Pig carcasses were treated with one of the three pesticides or water (control) at a concentration of 0.5% and placed in the field protected from scavengers. After initial appearance of larvae, samples were collected and separated into two sets. One set was analyzed by gas chromatography with mass spectrometry for detection of the pesticide and degradation products. The amount of pesticide present was also quantified. The second set of larvae was transferred to a non-treated food source. Subsequent samples from the carcasses and non-treated food source were analyzed and quantified at each instar stage. Controlled temperature experiments were conducted with the pesticides at the same concentration. After 24 hours of exposure to the pesticides, half of the first instars were transferred to a non-treated food source. Second and third instars from each group were analyzed and quantified. Correlations between continuous and limited exposure, variable and controlled temperature were examined.