The pre-colonisation period: What do we really know?

P.A. Magni; I. Dadour; D. Cook; S.C. Voss; W.F. Hung

Forensic entomology is the study of insects within a legal framework. The outstanding variable in determining an accurate post mortem interval (PMI) is the time that adult flies first lay live larvae or eggs onto a body. The predicted order of insects, typically blowflies and flesh flies that are attracted to a decomposing corpse or cadaver is pivotal to determining the PMI in forensic entomology. The predicted order is divided into primary, secondary and tertiary insects. This correlates with the process of decomposition and how it changes over time. Blowflies generally arrive after death and recent research has shown that Calliphora dubia, Calliphora varifrons and sarcophagid adults lay live larvae onto guinea pig carcasses within 1 hour of exposure. These flies are typically the primary visitors to a corpse. Very little is known about ovoviviparous blowflies, which are invariably the first blowflies to visit a corpse in south western Australia and are often the critical species in a PMI determination. New trials exposed 30 guinea pig carcasses throughout the day (0600-2000hrs) during spring and summer in bushland on each of 5 successive days. Replicate carcasses were set up randomly along a kilometre of bushland track and a carcass was removed every 0.5, 1.0, 2.0, 4.0, 8.0hrs throughout the day blowflies layed onto carcasses within 30 minutes (33% of carcasses), and on average on all carcasses within 1.5hrs of death. Eight different oviparous (e.g Lucilia sericata, Chrysomya rufifacies, Chrysomya varipes and Australophyra rostrata), and the oviviviparous fly species above deposited either eggs or live larvae onto the carcasses within 6hrs. This study highlights the previously unknown rapidity with which blowfly species are able to commence laying onto carcasses and from a large number of fly species, some of which are considered in the literature to be late colonisers of carcasses. Two repeat trials of exposure of carcasses again over 5 successive days in summer revealed 5 similar species of blowflies laid onto carcasses. This research has many ramifications for the post mortem interval estimation especially if all flies previously designated secondary and tertiary are in fact primary visitors to a corpse.

The pre-colonisation period: What do we really know?

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