Research article
The transfer of human DNA by Lucilia cuprina (Meigen) (Diptera: Calliphoridae)

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Abstract

Blowflies leave deposits, termed artefacts, through the processes of excretion and regurgitation. To date, little consideration has been given to the possibility of adult blowflies consuming biological material and subsequently acting as vectors of human DNA through these artefacts. In this study, Lucilia cuprina (Meigen) (Diptera: Calliphoridae) were fed either human blood or human semen ad libitum and their artefacts were analysed for human DNA content. Samples containing 1, 10, 30 and 50 artefacts were tested. Quantifiable and typeable levels of human DNA were found in samples derived from both food sources, and even in samples containing a single artefact. Semen-derived artefacts contained significantly more human DNA than artefacts produced after a blood meal. Consequently a smaller number of artefacts was required to collect sufficient DNA for genotyping. These findings are forensically important as it provides investigators with another potential source of DNA at a crime scene where a body has been moved, or an attempt has been made to clean up biological material. They also highlight how fly artefacts could potentially contaminate and compromise evidence.

Introduction

Flies leave spots that are termed ‘fly artefacts’ through the mechanisms of regurgitation and excretion [1]. These artefacts may vary greatly in colour, shape and size due to the different processes involved in their creation [2]. Spots may also be deposited by blowflies walking through liquid [1] but for the purposes of this paper ‘artefacts’ refer to faecal or regurgitation spots.

Fly artefacts can often be found at crime scenes where blood is present [1]. In some instances, it can be difficult to distinguish between these artefacts and blood spatter patterns, due to the similar morphology and high number of artefacts [1]. Consequently, it would not be unexpected for an investigator to sample fly artefacts in the mistaken belief that it is blood spatter. For this reason, it is important to know if blowflies can deposit a typeable amount of DNA as there is the potential for inadvertently collected DNA to interfere with the reconstruction of events or the evidentiary value of DNA profiles. Conversely, if fly artefacts are found to contain sufficient human DNA, they could prove to be a valuable source of DNA for investigators where a body has been moved or an offender has attempted to clean up biological material. Spitaleri et al. demonstrated it was possible to obtain an almost complete human DNA profile from a single mosquito blood meal stain, evidence which contributed to a second degree murder conviction [3]. Human DNA has also been successfully extracted and profiled at two loci from the excreta of adult human crab louse [4].

This research aims to determine if human DNA can be extracted from artefacts deposited by the forensically relevant Lucilia cuprina blowflies after they have fed on human blood or human semen, and the number of artefacts required to obtain a quantifiable and typeable amount of human DNA.

Section snippets

Fly experiments

Live blowfly pupae of L. cuprina were allowed to hatch in decontaminated, well-ventilated containers. In addition to water, the adult flies were supplied with human blood or human semen ad libitum. Biological material was stored at 4 °C until required and supplied to the flies within a week of extraction or ejaculation. Only a single source of blood and a single source of semen were used.

Once each replicate experiment had been set up, it was left for three days. This allowed time for sufficient

Blood meals

The threshold of 0.1 ng DNA to achieve full profiles was reached in 35%, 57%, 57% and 64% of samples containing 1, 10, 30 or 50 blood-derived artefacts respectively (Fig. 1). The median amount of DNA in the single-artefact group was below the detection limits of the Quantifiler™ kit. The 10, 30 and 50 groups had median DNA amounts of 0.60 ng, 0.47 ng and 0.72 ng respectively (Fig. 1). Regression analysis showed only a very weak correlation between the median amounts and the number of artefacts

Discussion

The results indicate that human DNA can be extracted from fly artefacts in sufficient quantities to provide a full profile of the donor.

The data suggest the amount of DNA in artefacts can be dependent on the meal type. Artefacts derived from semen contained significantly higher amounts of DNA than artefacts derived from blood. This is not surprising given the considerably higher content of DNA in semen when compared to blood [5]. Consequently, fewer semen artefacts are required to obtain a

Role of funding

Funding for this study was provided by La Trobe University, Australia.

Conflict of interest

None.

Acknowledgements

The author would like to thank the Institute of Environmental Science and Research (ESR), Auckland, New Zealand, and the New Zealand Police for funding and support during pilot studies. Further thanks go to Merilyn Geary of the Institute of Clinical Pathology and Medical Research, Westmead Hospital, New South Wales, Australia for supplying the blowflies.

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    Fly artefact documentation of Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae)—a forensically important blowfly species in Malaysia

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