Nocturnal oviposition behavior of blowflies (Diptera: Calliphoridae) in the southern hemisphere (South Africa and Australia) and its forensic implications

Abstract

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 (PMI) 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.

The uses of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) in forensic entomology

“…In good weather, an adult female can arrive at carcasses or other decomposing organic matter within a few hours of their appearance, and will usually lay a mass of 220–325 (mean ≈ 254) eggs on under-surfaces of these substrates [ 1 , 82 ] on the same day, preferentially near recently laid flies’ eggs [ 84 ], and providing that larvae of Chrysomya albiceps (Wiedemann, 1819) and Chrysomya rufifacies (Macquart, 1842) are not present [ 82 , 85 ]. Females are predominantly active during daylight, but have been shown to lay eggs at night under warm conditions [ 86 ]. Females of C. megacephala apparently prefer to walk to nocturnal oviposition sites [ 87 ].…”

Precocious natural mummification in a temperate climate (Western Cape, South Africa)

“…At the same time, exposed tissues of the carcasses would desiccate, inhibiting the carcass putrefactive activity of bacteria and fungi which require water to function and proliferate [33]. It is also known from the literature that gravid female blow flies will not oviposit on desiccated tissues due to the high susceptibility of eggs and young larvae to desiccation [6,[40][41][42]. This means that once favorable conditions for blow fly eggs and larvae resume the proportion of the resource available to them is reduced, which may negatively affect their survivability.…”

Thanatomicrobiome composition profiling as a tool for forensic investigation

“…For example, the succession of carrion insect species has been used to indicate PMI [ 44 ]. However, complex organisms are often unavailable during particular weather or season [ 45 ] and have variable developmental rates [ 46 ] and oviposition time [ 47 , 48 ], posing limitations in practices of PMI estimation. Therefore, patterns of succession of microbes have emerged as an alternative to higher organisms.…”