POST MORTEM INSECT SUCCESSION AND DEVELOPMENT PATTERNS ON DECOMPOSING PIG (Sus domesticus L) CARRION IN ELDORET AND MARIGAT, KENYA

Abstract

The death of human provides a decomposing media in the carcass/carrion which act as reservoir for rapidly changing habitat and food source for microorganisms and arthropods. The pattern of micro/macro-organisms succession on the decomposing carrion could be used as surrogate for determining important foresensic information. This method has not been used in Kenya in medicolegal/forensic investigations. This study determined post mortem insect succession and development patterns on decomposing pig (Sus domestica L) carrion in Eldoret and Marigat in Kenya. Decomposition followed all the stages (Fresh F for < 1 day, bloat B for 1-2 days, decay D for 3-8 day, advanced decay AD for 9 to 23 days, and and dry DR for 18 to 36 days). Stages F and B, were concomitant and for both carcasses but the rate of decay at stage AD was higher in Marigat than in Eldoret. Internal temperature at Marigat was significantly (P < 0.05) higher than that of Eldoret at all developmental stages, where it initially increased with progression of decay. Insect succession, species richness and abundance was high in Eldoret than Marigat. Insects including Lepidoptera that fed on carrion exudates, Hymenopterans as parasitoids, predatory Dermaptera were observed on the carcass upto advanced decay, while Diptera occurred at the fresh stage and bloat stage and lasted until the advanced decay with coleopterans colonizing the carrion late at decay stage and staying longer until the dry stage, most Hemiptera colonized at the fresh stage and stayed throughout the decay period without any significant change in their abundance. The succession pattern was similar in Eldoret and Marigat but they differed in their residence time. In terms of insect lifecycle: Diptera and Hemiptera laid eggs in fresh or bloat stage while coleopteran laid eggs at decay stage. The eggs hatched and developed to first and second larval instars during decay and progressed to third instars in advanced decay stage and the adult insects emmerged before the onset of the dry stage. However, only coleopterans with enzyme chitinase completed their life cycle in the dry stage. Also, the abundance of insect at bloat, decay due to fluidy status of the carrion, dry stages and advanced decay were positively associated with ambient temperature, soil temperature, relative humidity and wind speed that affects insects landing time for biological activities. Meanwhile, at each stage of decay, the combination of environmental factors that influenced the insect fauna was species specific. The study estbalsih that even in proximate geographic areas, the decomposition and insect succession are affected by the environmental variables.