Insects as vectors of DNA in a forensic context

Abstract

Insects have historically been used in criminal investigations to provide information in relation to postmortem intervals (PMIs) but the field of forensic entomology is expanding. It is now recognized that insects can act as vectors of human and mammalian DNA through the consumption of biological material, with extraneous DNA able to be extracted and genotyped from all stages of the life cycle, and insect feces and regurgitant (artifacts). To date, DNA recovered from insects have been used to inform investigations into neglect and homicide, link body parts, and to identify victims of crime. It may also potentially be used to identify assailants, confirm the food source of insects to determine their relevance in PMI calculations, determine if a crime has occurred, identify scenes of crimes, and link people to locations and other individuals. However, insects which have consumed biological material may also transfer DNA by traveling to new areas, or depositing it via their artifacts, either within crime scenes or laboratories, or at locations distant to the food source. This could contaminate forensic evidence, confound investigations, and/or falsely incriminate or exclude an individual. Therefore, it is important that there is increased awareness into both the utility of insects as vectors of forensically relevant DNA, and the potential for contamination. This article is categorized under: Forensic Biology > Forensic DNA Technologies Forensic Science in Action/Crime Scene Investigation > Crime Scene Examination Forensic Biology > Interpretation of Biological Evidence Forensic Biology > Body Fluid Identification

A DNA-based method for distinction of fly artifacts from human bloodstains

“…Moreover, given that in previous study the amount of human DNA increased over a time-span of 400 days, suggesting the presence of an inhibitor affecting the extraction DNA process losing its action over time [4], a chronological factor could be implied for negative fly DNA samples collected over 60 days. To evaluate this hypothesis, studies including different sampling times of fly artifacts will be developed.…”

“…Regarding the origin of DNA, we suppose that it could derive from fly cells or free DNA in the regurgitated or defecated spots. From this point of view, the reported "bubbling" behavior of flies could represent a source of DNA enrichment by the evaporation of water and concentration of food [4]. However, the modality of exude and reingested fluid by adult flies could lead also to nucleic acid degradation and might explain the failure of COI fragment amplification in our negative samples.…”

“…The detection of human DNA is generally the primary goal in a forensic genetic investigation, and also insects and their activity can provide very useful information to reconstruct a crime scene or a suspected one. The advancement of DNA analysis technologies has extended from the field of forensic application to forensic entomology where the ability to retrieve human DNA from insects has implications in terms of both contamination and as a potential source of DNA to be typed [4].…”

“…The implications for forensic science of the human DNA typing in fly artifacts originated from different biological fluids were described and include the identification of crime scenes, victims, and assailants, as well as the possibility to link person to person or person to action [4]. Further research should be addressed to identify COI sequence of fly's DNA on artifacts produced after feeding on other biological fluids and deposited on other substrates at different sampling times from deposition, considering that artifacts might remain at crime scenes for several months.…”

“…This is the case of insect stains defined as "bloodstains resulting from insect activity" by the Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN) [3]. Fecal, regurgitant, and insect-mediated transfer stains are known as artifacts, and when spots or specks of transfer patterns produced by flies are morphologically similar to bloodstains, the reconstruction of events at crime scene can be compromised [4]. Moreover, as blowflies feed on and digest biological fluids as blood, semen, and saliva, fly artifacts could contain sufficient amounts of human biological material to generate full or partial DNA profiles of the donor [5].…”