DNA Barcoding in forensic entomology

Forensic entomology has gained prominence in recent years, as improvements in DNA technology and molecular methods have allowed insect and other arthropod evidence to become increasingly useful in criminal and civil investigations. However, comprehensive faunal inventories are still needed, including cataloging local DNA sequences for forensically significant Diptera. 

Many kinds of insects will flock to a decomposing body, but the most common found on a corpse are flies and beetles. Flies, particularly blow flies, can find dead flesh within minutes. Their maggots do the majority of the eating and are responsible for much of a corpse's decay. Beetles, on the other hand, will typically move in once a corpse has dried out. Insects colonize a corps in successive waves, and each has its own unique life cycle. They can therefore provide information that is useful for estimating time of death (PMI - postmortem interval) and for learning about the circumstances of death.

Accurate species identification and up-to-date locality information are essential for the effective application of forensic entomology in criminal investigations, and an ever growing body of research has shown molecular data to be one of the fastest and most reliable methods of accomplishing species-level identification.

A new study from Central California describes the use of DNA Barcodes for forensic entomology and details the efforts of local researchers to build a comprehensive reference library. As part of a multi-year fly-trapping study flies from the families Calliphoridae, Sarcophagidae, and Muscidae were trapped in meat-baited traps set in a variety of locations throughout Santa Clara County. Samples were identified using morphological features and confirmed by DNA Barcoding.

Significant differences were found in fly fauna in even this relatively small geographic area, indicating the importance of microclimates in the distribution of these flies. The extensive collection of flies found in this study exceeded the previous records of fly species in this area, including finding previously undocumented species and larger-than-expected numbers of calliphorids, sarcophagids, and muscids previously assumed to be uncommon in the area. Flies collected in this study also form the basis for baseline data regarding the collection of local sarcophagid and muscid species, several of which have documented forensic significance. While morphological identifications can be made accurately with keys for the Calliphoridae and the Muscidae, current keys for the Sarcophagidae remain diffuse in the literature. However, our molecular analysis in this study supports the use of DNA sequences as a robust method of identifying cryptic fly species in the Central region of California.