The effect of morphine on the development rate of flies (Diptera: Calliphoridae, Sarcophagidae) reared on rabbit carcasses containing this drug and its implications to postmortem interval estimates

Abstract

Insects can prove to be a valuable tool in the estimation of PMI in the investigation of homicides, suicides, and other unattended human deaths, in the absence of tissues and body fluids. Aim: The current study aimed to determine morphine concentration in the second, third feeding, third post-feeding instars, and puparial skin of four forensically important flies; Lucilia sericata (Meigen), Chrysomya albiceps (Wiedemann), Chrysomya megacephala (Fabricius) (Calliphoridae), and Sarcophaga argyrostoma (Robineau-Desvoidy) (Sarcophagidae) and to evaluate its effect on the rate and pattern of development of these flies. Materials and methods: Three female domestic rabbits, Oryctolagus cuniculus (L.) each weighing 2.5 kg received dosages of 7.5, 15, and 30 mg of morphine over a 3-h period via left ear artery perfusion. For each trial, one other rabbit, weighing 2.5 kg, was used as a control. Morphine was detected in larval instars and puparial skin using ready to use RIA kit. Results: All blood and tissue samples obtained from the rabbits receiving dosages of morphine were positive for the drug. Morphine concentrations for rabbit R2 were 1.2 to 2.6 times greater than those for rabbit R1, and concentrations for rabbit R3 were 1.4 to 3.1 times greater than those for rabbit R2. For each rabbit, morphine concentration in second, third feeding and third post-feeding instars, and puparial skin for all four species, were less than those detected in the tissues. The highest levels of morphine were recorded in the feeding third instars of Chr. megacephala R3 colony, whereas the lowest level of this drug was detected in the feeding third instars of S. argyrostoma R1 colony. Estimations of larval age for L. sericata, Chr. albiceps, Chr. megacephala and S. argyrostoma based on mean length can be significantly in error if presence of morphine in the tissues is not considered. This error can be as great as 24, 27, 6 and 21 h respectively. Conclusion: In cases of badly decomposed and/or skeletonized remains, analyses of collected carrion-feeding insects, may provide the most accurate qualitative sources of toxicological information.