About the influence of burial on the development of forensically relevant blow fly larvae

The determination of the minimum post-mortem interval (PMImin) based on the age estimation of necrophagous blowflies is an established forensic technique. Blow fly larvae are able to continue their development to the adult insect on buried corpses. However, it is not clear which factors influence their viability under these circumstances or to what extent. This was investigated in the present paper for Calliphora vicina, one of the most common blowflies in Germany. In respect to forensic casework, an explicit question was if reference values obtained by rearing blowfly larvae under laboratory conditions could be applied to individuals growing in a shallow grave. Under variable ambient temperature conditions, hatched flies exhibited a slightly lower length of the wing veins (0.2 mm) and of the tibia (0.1 mm) than the larvae which had been buried. The period of development, expressed as accumulated degree days (ADD), was 399.8 in buried larvae and 406.1 in larvae not covered with soil as control. Under constant temperature conditions no significant differences in the body length of the larvae and the average time of development (20.3 respectively 20.4 days) was observed. The results of the present study thus suggest that the data published on the development of C. vicina larvae can be used to calculate the PMI of a corpse found in a shallow grave of not more than 20 cm depth.