ARS | Publication request: A molecular key for the identification of blow flies in southeastern Nebraska

Submitted to: Journal of Forensic Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2011
Publication Date: N/A

Interpretive Summary: When you watch the popular television series “CSI: Crime Scene Investigation” do you ever wonder how some of the ‘facts’ are gathered? Time of death and place of death (Was the body moved?), very important parts of an investigation, can be determined, in part, by the insects in and on a corpse. Blow flies are among the first ‘colonizers’; it is very difficult to confidently identify early stages of these flies. We used eight species of blow flies common in southeastern Nebraska, along with five other species of flies and one non-fly for comparison, to determine if molecular genetic techniques could be used to give additional, accurate forensic information. The technique of polymerase chain reaction – restriction fragment length polymorphism (PCR-RFLP) was used to compare the genetic ‘profiles’ of all 14 species. A portion of the mitochondrial DNA (a ‘rugged’ part of the total genetic information in living organisms) was amplified with PCR and then 10 common restriction enzymes were used to ‘cut’ the amplified DNA (RFLP). We found that a simple molecular taxonomic key, comprising just two restriction enzymes, produced patterns that enabled the differentiation of all species used in the study. The equipment for this technique is available in many crime investigation laboratories and therefore could be adapted to provide further information, as necessary, to solve crimes.

Technical Abstract: The identification of blow flies (Calliphoridae) (typically the first colonizers of cadavers) is difficult, especially in the earlier instars because of their small size, similarity and simplicity in external morphology. We consider how taxonomic keys based on molecular genetic data facilitate accurate identification and complement species identification, enhancing the applicability and utility of molecular diagnostics in forensic entomology. We examined the utility of a molecular taxonomic key, based on the mitochondrial Cytochrome Oxidase I (COI) region, to differentiate nine species of calliphorids commonly found in southeastern Nebraska. Restriction fragment length polymorphisms among species were investigated with ten common, inexpensive, restriction enzymes. A PCR amplicon of approximately 1500 bp spanning the mitochondrial COI gene was selected for analysis by PCR-RFLP. We found that a simple molecular taxonomic key, comprising just two restriction enzymes, produced patterns that enabled the differentiation of all species used in the study.