Date of Graduation
Eberly College of Arts and Sciences
Forensic and Investigative Science
he use of entomological specimens as a source of forensic DNA evidence has been studied since the late 20th century. Currently as it stands, to preserve both the minimum postmortem interval (mPMI) and DNA evidence within fly larvae, two standards of preservation exist. For mPMI, the use of hot water kill with near-boiling water is used to fix larvae size for accurate age estimation. For DNA evidence, the standard technique of preservation is submersion in 70% ethanol. To help reduce the number of standard preservation techniques for practitioners, this study assessed the feasibility of the hot water kill preservation technique using near-boiling water when obtaining short tandem repeat (STR) profiles from the contents of fly larvae crops (foregut). Reduction in the preservation techniques would result in the ability to collect only one set of specimens that could be used for both mPMI determination and DNA collection.
Lucilia sericata larvae were fed three different human livers, the crop tissue was removed from the larvae, and the human DNA from the crop contents was extracted. STR analysis, using standard crime laboratory procedures, was performed on the crops. Analysis of Variance (ANOVA) and Linear Regression Modeling was used to assess the variability around the means of two different preservative liquids, with five different residence times ranging from 30-300 seconds in 92-99°C water. Through the use of ANOVA, it was determined that the use of the hot water produced results that were not statistically different from the field standard using 70% ethanol as a preservation technique. The linear regression modeling found no significance in the ability to predict the proportion of alleles called in an STR profile based on the time larvae spent in the hot water kill bath. High variations in the proportions of alleles called within groups lead to weak correlation coefficients in the two linear models produced. With the ability to recover even partial STR profiles, the hot water kill technique can be utilized within forensic investigations related to cases in which a body may be missing while entomological specimen can be found or even cold cases that have already preserved fly larvae.
Studies assessing the feasibility of testing certain types of evidence like the one performed here can ultimately help practitioners by creating standard operating procedures that optimize the workflow within a laboratory.
Haas, Nicholas Alexander, "The Effects Hot Water Kill Time has on DNA Degradation and STR Profiling from Lucilia sericata (Diptera: Calliphoridae) Crop Contents" (2019). Graduate Theses, Dissertations, and Problem Reports. 7417.