The effect of substrates and time of deposition on molecular analysis of fly artifacts

The activity of animals and insects at the crime scene can provide useful elements to reconstruct the dynamics of the event. Any insect that interacts with wet body fluids can produce artifacts which can be confused with uman bloodstains. Considering that flies are the early colonizers of the crime scene and first players of the process of contamination, the problem is to distinguish stains produced by fly regurgitation or fecal elimination on a crime scene. Actually, fly artifacts are morphologically very similar to impact, projected, sneezed, and expirated bloodstains and cannot be reliably distinguished using presumptive or confirmatory tests for identification of human blood. Several techniques have been proposed to differentiate insect-derived artifacts based on morphological approaches and immunological assay. Recently, a DNA-based method by the analysis of the cytochrome c oxidase subunit I (COI) gene has been designed for the distinction of fly artifacts from human bloodstains on spots characterized by different morphological features and deposited by fly on a glass surface. Here, we present a study to assess the feasibility of the molecular analysis of fly artifacts deposited on different substrates as glass, paper, plexiglass and cotton and to evaluate the COI amplification success at different time intervals up to two years after fly artifacts deposition. Our results showed that the deposition time seems do not affect the detection of fly artifacts DNA, while a substrate interference was demonstrated.