The change in human DNA content over time in the artefacts of the blowfly Lucilia cuprina (Meigen) (Diptera: Calliphoridae)

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Abstract

Adult blowflies can act as vectors of human DNA by depositing faecal or regurgitation spots (termed artefacts) after feeding on meals of human biological fluid. Given the number of backlog cases in many forensic laboratories, it is important to know the maximum time period any human DNA within a fly artefact can remain unextracted before the DNA degrades to unusable levels. The present study aimed to determine whether or not the human DNA content in fly artefacts deposited by the blowfly Lucilia cuprina changed over time, and also to provide a timeframe for forensic biologists in which the extraction of human DNA from fly artefacts should be attempted. Both the blood and semen data showed that the amount of human DNA that could be extracted increased over the first 400 days, but had decreased to one-month levels by 750 days. The saliva data showed no changes over the 60-day time period in the amount of human DNA that could be extracted.

Introduction

Adult blowflies can act as vectors of human DNA by depositing faecal or regurgitation spots after feeding on meals of blood, semen [1] or saliva [unpublished data]. These spots – termed ‘fly artefacts’ – can contain sufficient amounts of human biological material to generate full or partial DNA profiles of the material donor [1]. Consequently, there is the potential for fly artefacts to contaminate genuine DNA evidence or be deliberately targeted as a source of DNA.

In situations where artefacts have been deliberately targeted by crime scene personnel, consideration must be given to how long the human DNA contained within remains typeable. Given the number of backlog cases in many forensic laboratories, it is important to know the maximum time period any human DNA in fly artefacts can remain unextracted before the DNA degrades to unusable levels. This is particularly crucial if the artefacts are the only potential source of DNA available.

This research aims to determine whether the human DNA content in fly artefacts deposited by the forensically significant blowfly Lucilia cuprina changes over time, and to provide a timeframe to forensic biologists in which the extraction of human DNA from fly artefacts should be attempted.

Section snippets

Materials and methods

L. cuprina were fed either human blood, semen or saliva ad libitum and left for 48 h. Cotton swabs were used to collect groups of 50 fly artefacts and stored at 25 °C until required. The human DNA component from the groups of 50 blood- or semen-derived artefacts was extracted and quantified after 3, 10, 30, 60 and 750 days (series one) or 3, 10, 30, 60, 250 and 400 days (series two). Fly artefacts derived from saliva were analysed for human DNA content after 3, 10, 30 and 60 days.

DNA extraction

Blood meals

Blood-derived fly artefacts did not exhibit a significant change in the amount of human DNA extracted over the series one time period (750 days). However, the data indicated a trend whereby the amount of human DNA extracted increased over the first 60 days, but had decreased to approximately 30-day levels by 750 days (Fig. 1). These changes were close to significant (P = 0.055, Kruskal–Wallis test) with the difference between 10 days and 60 days being the most. There was no significant change in

Discussion

The results indicate that human DNA can be extracted from fly artefacts derived from blood and semen for a period of at least two years after deposition, and from saliva for two months. It was interesting to note that the amount of human DNA that can be extracted from blood- and semen-derived artefacts increased over the first two months, with the increases being significant for semen-derived artefacts. It is possible that a component of the artefacts is interfering with the extraction process

Conflict of interest

None.

References (2)

Cited by (8)

  • Immunoassay detection of fly artifacts produced by several species of necrophagous flies following feeding on human blood

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    Fly stains are morphologically very similar in terms of shape, color and size to impact (i.e., forward, back, and mist-like spatter), projected, sneezed, and expirated bloodstains [4], and cannot be reliably distinguished using presumptive or confirmatory tests available for identification of human blood [8,9]. Molecular methods, namely those relying on DNA analysis, are also not effective at providing separation of insect from human stains since DNA profiles can be obtained of an individual from blood consumed by flies [10–12]. Techniques relying on morphological attributes of artifacts and alternate lighting have been reported to be useful in differentiating fly artifacts from human bloodstains [3,4,8,13], but all have limitations that prevent each from being consistently reliable for use in crime scene investigations.

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