Nocturnal oviposition behavior of blowflies (Diptera: Calliphoridae) in the southern hemisphere (South Africa and Australia) and its forensic implications
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Published research has offered contradictory evidence of the occurrence of nocturnal oviposition by carrion-breeding blowflies, a behavior that can affect the interpretation of forensic estimates of a minimum post mortem interval (minPMI) by up to 12 hours, depending on latitude and season. The majority of published studies are from the northern hemisphere. Field experiments were conducted in South Africa and Australia that extend observations to species of the southern hemisphere. Various vertebrate carrion was exposed at night in summer under different lunar phases and/or artificial lighting, and in woodland and pasture areas. Three laboratory experiments were also conducted. No nocturnal oviposition occurred outdoors in Berry, Australia, but Lucilia cuprina, Lucilia sericata and Chrysomya megacephala laid eggs outdoors at night in Grahamstown and Durban, South Africa. In laboratory experiments L. sericata, L. cuprina, Chrysomya chloropyga and Chrysomya putoria laid eggs and Calliphora augur deposited larvae under nocturnal conditions. Chrysomya albiceps and C. chloropyga laid eggs in darkness with increasing likelihood as ambient temperature increased. This study shows that nocturnal ovi/larviposition by carrion-breeding blowflies is possible in both South Africa and Australia. The forensic issue is therefore not whether nocturnal oviposition occurs, but rather whether the conditions of a particular case are more or less conducive to it. Circadian rhythms and physiological thresholds (particularly temperature and humidity) appear to act individually and in conjunction to stimulate or inhibit nocturnal laying. The significance of carcass size, freezing and handling of carcasses and comprehensive quantification for experimental design is discussed, and recommendations are made for future laboratory and case scene experiments.
KeywordsBlowflies Flesh flies Forensic entomology Circadian rhythms Minimum post mortem interval
The authors thank the following for technical and field assistance: Kendall Crous, Natasha Govender, Unathi-Nkosi Heshula, Tembisa Jordan, Million Kota, Nolindile Sali, Philip Weyl and Zonwabele Zenani (South Africa) and Colin Cortie, Aidan Johnson, Gae and John Lessard, Kelly Meiklejohn, Erin Marshall, Elizabeth Neale and Leigh Nelson (Australia). The authors are also grateful to John Keulder and Emil von Maltitz for the loan of light meters and Mark Benecke for providing literature.
Compliance with ethical standards
This research was funded by the National Research Foundation (NRF) of South Africa and William Waddell Trust Fund funded D.N. Mazungula. Any opinion, findings and conclusions or recommendations expressed in this material are those of the authors and the NRF does not accept any liability in that regard.
Conflict of Interest
All authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All South African species used in this study are neither CITES-listed species nor endangered species according to regional Red Lists or South Africa’s Threaten or Protected Species (ToPS) legislation. As such no special sampling permission is necessary for taking samples in South Africa.
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