The effects of burning on carcass decomposition and associated insect succession in Western Australia

This study aimed to assess the effect of burning a carcass on rate of decomposition and insect succession in Western Australia. Previous research in respect to burnt remains is severely limited (three studies), not applicable to Australian conditions and hindered by low replication and infrequent sampling. This study addressed this deficit of knowledge using both higher replication and sampling frequency under conditions specific to an Australia outdoor death scenario. Ten pig carcasses (40 – 45 kg), all sacrificed by humane captive head bolt were used in a single trial during the autumn months (March – April) of Western Australia. Five pig carcasses were burnt to a Crow-Glassman Scale (CGS) level #2, while five carcasses were left unburnt as controls. Carcasses were exposed in a secure bushland research facility, 23 km south of the Perth Central Business District. The trial covered 42 experimental days, where sampling was conducted every day for the first 15 days and then every other day until Day 42. During this time, rate of decomposition and associated insect succession was assessed.

Progression through the physical decomposition stages were greatly accelerated in burnt carcasses compared to unburnt carcasses, due to the loss of dermal fluid and the leathery consolidation of skin as a result of burning. Early stages of decomposition (fresh and bloat) were almost non-existent in burnt carcasses, as four replicates had already progressed into the wet phase within the first 24 hours of sampling. The insect species identified on carcasses were ubiquitous to both treatment groups with the exception of Staphylinidae sp which occurred on a single burnt carcass but not on any of the control carcasses. While species were essentially consistent across treatment groups, differences were noted in the arrival time of late colonisers (Coleoptera) and the development of colonising insects between treatment groups. Insect assemblages were significantly different between the two treatment groups (burnt and unburnt) (PERMANOVA: F (1, 224) = 14.23, p < 0.01) during an eight day period (Day 6- Day 13) throughout the wet stage of decomposition.

Differences in the duration of decomposition stages and insect assemblages indicate that burning has an effect on both rate of decomposition and insect succession. Few studies have been conducted worldwide on the effect of burning and none in Australia. Comprehensive data pertaining to the effect of burnt carcasses on decomposition and associated insect succession are documented. The results from this study provide essential geographic specific baseline data for entomological casework in Australia and potentially worldwide.