The nocturnal oviposition behaviour of blowflies (Diptera: Calliphoridae) in Central Europe and its forensic implications.

Numerous factors may cause delayed colonisation of a corpse by blowflies, leading to a discrepancy between the entomologically determined post-mortem interval (PMI) and the time of death. Blowflies, for example, are considered to be inactive at night, however, published observations are contradictory. In the present study, several field experiments and one type of indoor experiment were conducted in summer of 2004 and 2005 in order to investigate the nocturnal ovipositional behaviour of blowflies. In the field, two types of bait, dead hedgehogs and fresh beef liver, were placed at night in different urban and rural locations in Frankfurt and in Munich, Germany. For the indoor-experiments beef liver was placed in small plastic boxes containing caged Lucilia sericata females in the evening and left overnight. At night, no ovipositon was observed in the field (n=51, T=10-24 degrees C). Nocturnal oviposition in complete darkness occurred in the plastic boxes in two of six cases (T=25 degrees C). Considering the behavioural and physiological characteristics of flies we suggest that nocturnal oviposition of blowflies appears to be unlikely under natural conditions in Central Europe but may occur under certain circumstances, such as unusual high nightly temperatures and the presence of gravid flies with an appropriate arousal threshold.