Succession patterns of sarcosaprophagous insects on pig carcasses in different months in Yangtze River Delta, China

Abstract

The Yangtze River Delta is one of the most economically developed regions in China, and many cases in the area require an estimation of the postmortem interval each year. This article reports forensic entomological research conducted in this region in different months. A total of 18 domestic pigs were used to study carcass decomposition, species composition, development events, and succession patterns of insects in different months from 2015 to 2021. A total of 53 arthropod species were identified, of which 38, 40, 41, and 25 were observed in April, June, September, and November, respectively. We demonstrated that insects vary in number and species from month to month, and the same species vary in number among the different months. Larvae of Calliphoridae mainly drove the decomposition of carcasses, and the decomposition rate of carcasses varied over the months. Particularly, the decomposition rate was highest in June and September, slower in April, and slowest in November. The predominant species on the carcasses also varied from month to month; Calliphora grahami Aldrich, Chrysomya pinguis (Walker), Lucilia sericata (Meigen) (Diptera: Calliphoridae), and Hydrotaea spinigera Stein (Diptera: Muscidae) were most predominant in April; Chrysomya megacephala (F.) and Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae) were most predominant in June and September; and Ca. grahami was most predominant in November. In addition, the seven dominant insect species displayed four developmental events, which could be used to determine minimum postmortem interval, including adult arrival (T1), larvae wandering (T2), pupation (T3), and eclosion (T4) time on the carcasses. Insect succession patterns on carcasses also varied across months. For example, Ch. megacephala appeared later in the composition stages and was not numerically dominant in April but appeared earlier and was dominant in June and September. The results of this study guide the use of insect evidence in different months in the Yangtze River Delta region of China for estimating the postmortem interval of carcasses.