Succession Pattern of Insects of Forensic Importance on Pig (Sus scrofa Linnaeus) Carrion in Lagos and Kaduna States of Nigeria

Abstract

Succession patterns of insects on pig carrions at Ojo, Lagos (South-western) and Samaru, Zaria (North-central) Nigeria were monitored during the rainy and dry seasons of 2011-2013. Ambient, maggot mass, and soil temperatures, precipitation and relative humidity were measured. A total of 118 species belonging to 12 Orders and 49 Families were identified, out of which 25 species were common to both regions. Decomposition occurred in five stages. The earliest arrivals on the carcasses were the dipterans and hymenopterans followed closely by the coleopterans. Chrysomya chloropyga (Wiedemann) and Musca domestica (Linnaeus) were the most abundant necrophagous insects attracted to pig carrions on the 1st day of exposure; these flies aggregated around the carrions at both locations. Adult Sarcophaga exuberans (Pandelle) were collected during the fresh and bloated stages of decomposition although they arrived late. Most predominant coleopterans collected during the bloated stages were Necrobia rufipes (De Geer) and Dermestes maculatus (De Geer) at both regions. Camponotus perrisi (Forel) and Camponotus sericeus (Fabricius) were the most predominant predators during the early stages of decomposition at Ojo while Pheidole liengmei (Forel) was more predominant at Samaru during the same stage. The decay stages (active and advanced) attracted more coleopterans of the families Histeridae, Melyridae and Stapylinidae with Melyris abdominalis (Fabricius) being the most predominant at Samaru and N. rufipes at Ojo. Skeletonization stage of decomposition were not devoid of insects with dipteran species such as M. domestica was observed during the wet seasons in Ojo and coleopterans which included Alphitobius laevigatus (Fabricius), Sphaerocoris annulus (Fabricius) and N. rufipes and hymenopterans such as Myrmicaria striata (Stitz), P. liengmei and Messor galla (Mayr) were collected in Samaru. Atherigona occidentalis (Deeming), Asphidomorpha cincta (Fabricius), Sarcophaga inzi (Curran) and Saprinus pennsylvanicus (Paykull) were found exclusively at Ojo while Chrysomya regalis (Robineau-Desvoidy), Isomyia evanida (Villeneuve), M. abdominalis and Tricyclea perpendicularis (Villeneuve) were found only at Samaru. Jaccard similarity index showed similarity in the succession pattern of insect species at Ojo and Samaru during the rainy (0.79± 0.006) and dry (0.78±.0.005) seasons. Taxa diversity increased from the fresh stage to decay stages and thereafter declined during the dry stages. Species diversity was higher during wet seasons (121) than in the dry seasons (90). Temperatures varied between seasons, and relative humidity was significantly (P < 0.05) higher at Ojo than at Samaru. Some of the species occurring exclusively in seasons and regions may be important to characterize between location and seasons.