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Fields & Applications Mass Spectrometry, Thin Layer Chromatography, Forensics

Fly in the Face of Evidence

Analysis of insect eggs on corpses at different stages of development can provide a time window for forensic experts – but it can be difficult to distinguish similar species without using expensive and often time-consuming techniques such as DNA profiling. Now, an organic chemist and forensic entomologist have teamed up to develop a quicker and cheaper method for analyzing the eggs of different blow fly species. Jennifer Rosati, Professor of Forensic Entomology in the Department of Sciences at John Jay College of Criminal Justice, New York, USA, tells us more.

How did your research begin?

Rabi Musah (Associate Professor, University of Albany, New York, USA) and I met at a forensic symposium – she presented her work on using DART-MS for the identification of psychotropic compounds in plant material, while I presented my work on understanding blow fly behavior and its importance in post-mortem interval (PMI) estimations. She approached me to offer her chemical expertise to my study system and suggested that DART could also be useful in forensic entomology. From there we began to forge our relationship and are in the process of incorporating the use of DART-MS in many aspects of forensic entomology.

Could you tell us a little more about your method?

Freshly laid eggs were collected from multiple necrophagous fly species, including representatives from the blow fly family (Calliphoridae), specifically Calliphora vicina, Lucilia sericata, L. coeruleiviridis, and Phormia regina species as well as the Phoridae and Sarcophagidae families. We analyzed the eggs by DART-HRMS, determining that species-specific differences are correlated to the amino acid profiles of the insects. The presence of these free amino acids in the egg samples was also confirmed through the use of MALDI-SpiralTOF-HRMS, as well as thin-layer chromatography.

What impact will this discovery have on forensics?

Current practices in the field of forensic entomology involve many hours devoted to insect rearing and species identification, which can be difficult, particularly during the immature stages of development. In fact, very few identifications are carried out on egg or larval samples. This technique could offer quick and rapid identification for all life stages, as well as verification for adult identifications. Our published findings are really just the tip of the iceberg when it comes to using DART-MS in the field of forensic entomology. This technique could easily be utilized in many other forensic fields, from forensic toxicology to fingerprint analysis. Our next step is validating this technique for other forensically relevant insect species and also looking at its use in entomotoxicology.

Has this technique been used in a real life setting?

I recently took on a case where a large egg mass was collected and preserved from human remains, which is typically unusable evidence. Though I have already reared the larvae that were also collected from the remains, I plan to use this technique to verify my adult identifications and to also determine the species composition of the egg mass. A forensic entomologist is frequently questioned on the stand regarding their ability to carry out species identification correctly. By utilizing this technique, I’ll provide independent validation of my species identification – which will remove any subjectivity in my analysis and allow me to reliably incorporate the proper developmental data into my colonization estimate. To be able to employ this research technique immediately into an applied forensic setting is very exciting.

The Science and Nothing But the Science, with Craig O’Connor
One Piece of the Puzzle, with Kacey Cliburn
Fly in the Face of Evidence, with Jennifer Rosati
Battling the Backlog, with Sarah Lum and Charlie Clark

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  1. JE Giffen et al., “Species identification of necrophagous insect eggs based on amino acid profile differences revealed by direct analysis in real time-high resolution mass spectrometry”, Anal Chem, (2017). Available at: bit.ly/2uMuvhz. Accessed July 11, 2017.
About the Author
Jennifer Rosati

Jennifer Rosati is Professor of Forensic Entomology in the Department of Sciences at John Jay College of Criminal Justice, New York, USA.

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