Studies on Variation in Texas Blow Flies (Diptera: Calliphoridae)

Blow flies (Diptera: Calliphoridae) are the primary invertebrate consumers of carrion. Due to their close association with decomposition throughout their lifecycle, immature Calliphoridae collected from remains can be used to predict the time of colonization (TOC) and infer the postmortem interval (PMI). Although entomological evidence and scientific expert testimony are admissible in a court of law the accuracy and precision of insect age estimates is unknown. This dissertation research addresses different approaches for improving insect age estimates. A survey of calliphorids stored in state museums revealed a total of 21 forensically important species had been collected in Texas; their temporal and spatial distributions were documented. Survey data shows that Cochliomyia macellaria (Fabricius) and Phormia regina Robineau-Desvoidy are widespread, and that invasive Chrysomya species are present across the state. The survey also identified the need for local development data for forensically relevant Calliphora coloradensis Hough and Calliphora livida Hall. To quantify the variation associated with the pre-appearance interval (PAI) of C. macellaria, an ecological model was developed. Results indicate that PAI is a potential important source of error and that an ecological model is one way to evaluate its impact. This model can be re-parameterized with any development data set, PAI function, temperature regime, or assumption of interest to estimate insect age and quantify uncertainty that arises from specific prediction systems. A C. macellaria development data set was tested in outdoor conditions to assess its accuracy in predicting age. Results show length, weight, and stage predictions with the development data set were generally accurate but imprecise for individuals past the second instar. This validation allows forensic entomologists to quantify expected accuracy derived from insect age estimates when using this development data. Forty-five candidate genes were selected for gene expression analysis in the third instar and pupal stages of L. sericata. Results show that 10 of the genes are promising markers that when used in combinations may be useful for distinguishing age within stage. These results support the use of gene expression to break lengthier stages into smaller temporal pieces, which improves the precision of insect age estimates