Date of Award

1-1-2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Chemistry

Content Description

1 online resource (xxvii, 306 pages) : color illustrations.

Dissertation/Thesis Chair

Rabi A Musah

Committee Members

Jennifer Y Rosati, Paul Toscano, Ting Wang

Keywords

Ambient ionization mass spectrometry, Calliphoridae, Forensic Entomology, Necrophagous insets, Species identification, Mass spectrometry, Blowflies, Forensic entomology, Carrion insects, Decomposition (Chemistry), Biodegradation, Biodegradation, Environmental, biodeterioration

Subject Categories

Chemistry

Abstract

Forensic entomology is the study of insects that colonize human/animal wounds and remains and their development for use in legal contexts. It has numerous facets and applications including: estimation of time since death; investigation of neglect/abuse of children and the elderly; and determination of the presence of toxins and drugs as a potential cause of death. In order for the discovered insects to be of forensic utility, accurate species identification is crucial. Current methodologies for species determination rely on the knowledge and expertise of an entomologist; exhaustive taxonomic keys; and access to adequate equipment and facilities; resources which are often not available during the course of most medico-legal investigations. Additionally, the lack of statistical certainty associated with conventional means for identifying recovered evidence is problematic, especially when considering that the entomological samples may be admitted as evidence during criminal proceedings. Molecular methods are often costly and time-intensive. Additionally, the molecules responsible for the attraction of necrophagous insects to wounds, corpses and carrion are not well characterized, and the identities of most of these compounds remain unknown. This knowledge gap exists in part because of: (1) the difficulties associated with teasing apart the correlations between decomposition stage, the molecules characteristic of that stage, and the insects that are attracted at a given stage; (2) the impact of external factors such as temperature, geography, climate, as well as manner of death etc., on decomposition; and (3) the challenge of detecting and identifying the subset of molecules, out of a mix of hundreds or even thousands that may be present, that influence fly behavior.By utilizing the ambient ionization source direct analysis in real-time (DART) with time-of-flight high-resolution mass spectrometry (HRMS), it is possible to generate unique species-specific chemical fingerprint profiles for entomological evidence that is analyzed directly in the vii form in which it is collected at crime scenes. The spectra are acquired rapidly, which enables the generation of the thousands of replicates required to perform the chemometric processing that can in turn provide species identification predictions with a defined level of accuracy. Presented here are the results of the analysis of six species of blow flies during each of their four distinct developmental stages by DART-HRMS. This yielded chemical fingerprint profiles that were unique for each species and developmental stage. The collected data were then used as the basis for proof-of-concept multivariate statistical analysis models that were between 84 and 100% accurate for predicting the correct species identity, depending on the life stage analyzed. Additionally, similar mass spectrometric techniques performed in tandem with solid phase microextraction, were used to collect and characterize the profile of volatile chemicals that are emitted from carrion surrogates and necrophagous insects over short periods of time. The headspace volatiles emitted from the eggs of two species of blow flies, which are proposed to be a source of conspecific and heterospecific insect attraction, were analyzed for the first time using this system. The observed chemical profiles revealed a number of interesting trends: the signatures generated for each species were unique, and covered a wide range of chemical classes including alcohols, aldehydes, amines, ketones and sulfur-containing molecules; further, several compounds that are often reported to be associated with the process of mammalian decomposition were identified to be emitted from the eggs. These compounds, as well as others identified from the headspace of recently slaughtered chicken livers, were offered to captive blow flies in order to begin identifying potential attraction cues. Several chemicals, including ethanol, crotonic acid and 2-hydroxy-γ-butyrolactone, were shown to elicit a number of attraction behaviors and even resulted in oviposition (egg laying).

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