The Impact of Soil Type and Cohort Size on Pupation Depths for the Forensically Important Blow Fly, Phormia regina (Diptera: Calliphoridae)

Forensic entomology is the study and use of insect evidence in a legal investigation. The collection, processing, and analysis of insect evidence in court cases often falls upon law enforcement or medical examiner personnel on scene. Given many times the individuals collecting entomological evidence on scene are not trained in entomology, guidelines for collection of this type of evidence are crucial. A newly established standard for the collection of entomological evidence proposed by the Organization of Scientific Area Committees (OSAC) states a collection depth of 10 cm for the collection of pupal evidence found in the ground. This standard largely lacks empirical data supporting this value, in this thesis, the depth of pupation was tested using a custom-built apparatus that limits the distance the larvae travel horizontally before vertical burial. Two soil substrates, one locally sourced and another commercially available, were used to analyze burials depths for the forensically important blow fly, Phormia regina. The soil samples were analyzed to better understand the different properties present (moisture, soil compaction, temperature, and pH) in the soil during these testing phases. Beyond the testing of two soil substrates, cohort size (groups of 30, 60, and 120 larvae) and larval weight were investigated as factors to see if changes would have an impact on the depth of pupation. The soil type was the factor that mostly impacted burial depth, as cohort and weight had little influence. With the expanse range of P. regina understanding how the different soils changed the depth at which the larvae pupated indicates that in locations where the soil is less compacted the depth of pupation is impacted. This result suggests that collection at only 10 cm depth could inadvertently exclude insect evidence that otherwise could be useful thus hindering more accurate postmortem interval estimations.