Spatial and temporal variation in carrion blow fly communities: Applications to forensic entomology



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Texas Tech University


Seasonal and regional carrion decomposition studies were conducted in three geographic regions in Texas. Seasonal studies were replicated during the spring, summer and winter, for three consecutive years. Regional studies were replicated in one season (summer) for three consecutive years.

Domestic pig carcasses (N=3) were placed 200m apart in each of the three study sites. Carcasses were monitored during the decay process to document spatial and temporal variation in decay patterns and in the composition of the associated blow fly communities.

Distinct patterns of decomposition and distinct blow fly communities were correlated with season and these patterns were similar among geographic regions. However, the abundance of certain blow fly species did vary significantly by year.

During pilot studies, Cochliomyia macellaria (F.) were the most abundant flies at all three sites. Thus, this species was the emphasis of two major sections of the dissertation: (1) an investigation of variation in wing morphology among populations across years, and (2) mitochondrial DNA variation among populations of C. macellaria.

In the morphological study of C macellaria, 25 characters were measured from the right wing of each specimen in order to investigate intraspecific variation. Multivariate statistical analyses were performed, and significant variation was found among populations and across years.

In the molecular study of C. macellaria, the entire cytochrome oxidase subunit II (COII) gene was sequenced (693bp) for each individual in order to investigate intraspecific variation. Regional variation was documented among the three geographic locations. DNA sequences generated in this study are deposited in GenBank.

Results from this dissertation are discussed in terms of their application to forensic entomology. Entomological evidence collected from crime scenes can assist criminal investigations in numerous ways. Community succession and insect developmental timing can be used to establish a postmortem interval (PMI or time since death). Geographic distributions can be used to determine whether human remains have been relocated following death.

This work is the first replicated decomposition study in the state of Texas and contributes significantly to a growing national database in forensic entomology. It is the only fully replicated study, in any US state, to extend across three consecutive years. In addition, this dissertation is the first study to apply both molecular and multivariate statistical techniques to forensic entomology, in an effort to enhance the detection of postmortem relocation of human remains.



Blowflies -- Texas -- Evolution, Forensic entomology, Postmortem changes, Blowflies -- Texas -- Genetics, Indicators (Biology)