Two major factors that influence the development of calliphorids are biogeoclimatic factors and presence of toxic substance. In geographical regions with defined seasons such as summer, spring, autumn and winter in a year, the growth rate of insects has been found to be influenced by sunlit and the shaded habitats as well as the difference in seasons, largely due to the differences in ambient temperature. Moreover, rain in general, inhibits adult activity and prolongs the development of Calliphorids. In the context of Malaysia being different in its yearly seasons as well as annual rainfall, review of the literature does not reveal research on the development of calliphorids as influenced by less rainy and rainy seasons or heavy and/or incessant rain that are commonplace in this country.
In addition, studies have shown that the development of Calliphorids can be influenced by drugs and poisons. It has been reported that opiates and amphetamines accelerate the development of both Lucilia sericata (Calliphoridae) and Parasarcophaga ruficornis (Sarcophagidae). On the other hand, no difference was observed in the development of Parasarcophaga ruficornis larvae reared on tissues that contained therapeutic drugs (amitriptyline and phencyclidine) when compared with that in controls. In a case of suicide using malathion, Gunatilake and Goff (1989), stressed on the importance of considering the possible effect of the ingested malathion on the development of C. megacephala and C. rufifacies. In a laboratory-controlled study, the larval stages of C. megacephala reared on dissected liver tissues obtained from the malathion-exposed rats, were observed to be longer when compared with that in control (Abd-Rashid et al., 2008). In this context, it is pertinent to quote that any factors mitigating insect development have the potential of affecting subsequent insect-based estimates of postmortem interval. However, review of the literature does not indicate data relating to the influence of the different concentrations of ingested malathion in a whole decomposing carcass on initial oviposition and development of calliphorids under field conditions. On the other hand, it has been found that there has been an apparent increase in the incidence of drug related death and in many of such cases the bodies are not recovered for a substantial period of time. In the context of poison related death in Malaysia, it is seen that malathion is more prevalent. Thus, it was found pertinent to study the influence of ingested quantities of malathion in decomposing carcasses on calliphorids development.
Our results (Mahat et al., 2009) reveal that rain, depending on its intensity, delayed initial oviposition by 1-2 days and prolonged the pupation period by 1-3 days. The presence of the different concentrations of malathion in the carcasses delayed initial oviposition by 1-3 days and prolonged the pupation period by 2-3 days. Presence of rain and malathion cumulatively prolonged pupation period that extended to a maximum of 8 days. The novel finding of this research is that, temperature apart, rainfall of about 9.0 mm or more a day during the period of pupation that rendered the soil wet consistently prolonged the period of pupation. It was found that the maximum of such prolonged period of pupation attributable to the influence of rain was eight days, while the maximum period of pupation in the absence of rain in sunlit habitat was only three days. Pertinently, Greenberg and Kunich (2002) recognized that larvae failed to pupariate when kept in constant contact with water and cautioned that overlooking the fact that rain-soaked soil delays development would lead to inaccurate estimation of time of death. The prolongation of period of pupation attributable to rainfall during the period of pupation is a unique finding that needs to be considered while estimating PMI whenever pupae are found in crime situations with similar weather conditions.
The full text article of our study published in the Forensic Science International is accessible via ScienceDirect database (subscription is required).
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