Abstract:  In order to solve the difficulty of the determination of postmortem interval （PMI） in criminal cases,  18 pig carcasses were placed in outdoor environment in different seasons to observe and select the critical entomological index in accurately estimating of PMI. The results showed that these indexes, including T1 (larvae begin to appear), T2 (larvae begin to crawl away), T3 (most of the larvae have crawled away), T4 (larvae begin to pupate), T5 (most larvae have pupated), T6 (pupae begin eclosion) and T7 (the end of eclosion), could be used as accurate PMI indicators for their high sensitivity and stability. The carcasses decayed very quickly in spring, summer and autumn, and it took 202±23 h, 202±18 h, 277±20 h for test carcasses to decay from fresh to skeleton in these seasons, respectively. In winter it took a longer time of 1 297±63 h to decay from fesh to skeleton. About 47 insect species were found on carcasses. Most of the necrophagous insects could be found all the year, and there was no marked difference in species composition among the four seasons. The predominant species were very apparent. The fly larvae included mainly Chrysomya megacephala, Achoetandrus rufifacies and Hydrotaea (Ophyra) spinigera. The necrophagous insects could only breed one generation on carcasses before the carcasses become into skeleton in most of the time. Based on these results, critical time points for PMI estimation could be determined.

Key words: Forensic entomology, body decomposition, insect succession, postmortem interval estimation, time points