Annual variation in arrival and departure times of carrion insects at carcasses: implications for succession studies in forensic entomology

Abstract

A succession of insect species associate with decaying bodies, and because of the relatively predictable arrival and departure times of many species, this process is routinely used to estimate minimum post-mortem interval. Corpse fauna are compared with baseline data on succession rates, which are usually taken from decomposing animal carcasses. Baseline data are traditionally collected over a single year only; however, annual differences in weather patterns and insect population parameters probably alter succession rates. Surprisingly, this potential source of error has not previously been examined. Therefore, a two-year succession experiment was performed to investigate annual variation in succession rates. Sets of five still-born piglet carcasses were placed in a forest each season of both years. Six insects that occur year-round were selected: adults of Aleochara brachialis Jekel, Anotylus spp., Creophilus erythrocephalus Fabricius (Staphylinidae: Coleoptera), Ptomaphila lacrymosa Schreibers (Silphidae: Coleoptera), Pseudonemadus spp. (Leiodidae: Coleoptera), and larvae of Calliphora spp. (Calliphoridae: Diptera). Arrival and departure weeks to and from carcasses were measured in each season of both years. Two-way ANOVAs revealed significant season and year interactions on the arrival weeks of Anotylus spp., C. erythrocephalus, and Pseudonemadus spp., and significant differences in seasonal and yearly arrival times for A. brachialis, and P. lacrymosa. For larvae of Calliphora spp., there was a significant seasonal effect on arrival times. A significant interaction between season and year affected the departure weeks of all taxa. These results show that error in the estimates of minimum post-mortem interval can result if baseline succession data are collected only over one year.