Investigations Toward Development of a Technique for Rapid Identification of Forensically Relevant Necrophagous Beetle Species for Postmortem Interval Determination

Entomological evidence can be used to estimate postmortem interval (PMI) in death investigations. Carrion insects facilitate the estimation of PMI through consideration of the well-known correlation between the timing of their colonization of remains, the timing of their species-specific life cycles, and the stage of the decomposition of the remains. The accuracy of the prediction is contingent upon correct identification of the species of the retrieved insect evidence. Conventional methods for identification of the insects require that an experienced entomologist rear the immature insects, such as the larval stages, to maturity so that species determination can be made based on the gross morphological features of the adults. This must be done because the larvae are visually similar in appearance and therefore their species identity determination is challenging. Other approaches that aim to identify the visually similar immature life stages of insects, like DNA-typing, are expensive, time-consuming, and limited by the lack of a full, comprehensive database of insect genome profiles against which comparisons can be made. Yet, beetles are particularly important for remains that have progressed to more advanced decay stages, where PMI estimates can be quite difficult to make. Proposed herein is the development of a species identification approach for carrion beetles that enhances their utility in forensic investigations for the assessment of postmortem interval. It leverages the finding that some insects have been shown to exhibit species-specific chemical profiles which when processed by machine learning tools, can accurately predict species identity in the absence of any other information (such as DNA profiles). Thus, creation of a database of the chemical signatures of beetle species provides a mechanism by which chemical profiles of unknowns can be screened in order to rapidly acquire species information that can be used to estimate PMI in difficult cases. Chemical profiles will be rapidly determined using direct analysis in real time – high-resolution mass spectrometry (DART-HRMS) for beetles from the Silphidae family, as these are arguably some of the most important necrophagous insects that are widely distributed on the North American continent. The confirmed identity of the beetle species, coupled with existing life cycle pattern data, will enable more rapid and reliable estimation of the postmortem interval. Practitioners will be able to screen the DART-HRMS profiles of retrieved larval evidence sample unknowns against the database to rapidly identify species so that entomological keys can be efficiently used to assess PMI. CA/NCF