Factors Affecting Species Identifications of Blow Fly Pupae Based upon Chemical Profiles and Multivariate Statistics.

William Kranz,Clinton Carroll,Christine Picard,John Goodpaster,Darren Dixon

doi:10.3390/insects8020043

Abstract

Alternative methods for the identification of species of blow fly pupae have been developed over the years that consist of the analyses of chemical profiles. However, the effect of biotic and abiotic factors that could influence the predictive manner for the tests have not been evaluated. The lipids of blowfly pupae (Cochliomyia macellaria, Lucilia cuprina, Lucilia sericata, and Phormia regina) were extracted in pentane, derivatized, and analyzed by total-vaporization solid phase microextraction gas chromatography-mass spectrometry (TV-SPME GC-MS). Peak areas for 26 compounds were analyzed. Here we evaluated one biotic factor (colonization) on four species of blow flies to determine how well a model produced from lipid profiles of colonized flies predicted the species of flies of offspring of wild-caught flies and found very good species identification following 10 generations of inbreeding. When we evaluated four abiotic factors in our fly rearing protocols (temperature, humidity, pupation substrate, and diet), we found that the ability to assign the chemical profile to the correct species was greatly reduced.

Highlights

Insects make up a large proportion of the environment; it is not surprising that insects would be present in crime scenes
Insects recovered from the body can be used as a “clock” to determine the minimum postmortem interval (PMIMIN ), or the time since the body has been available to the insects, as most species in North America will only lay eggs or larvae on a resource if it is dead [2,3]
Considerable chemical differences were documented among Cochliomyia macellaria, Lucilia cuprina, Lucilia sericata, and Phormia regina as a function of species and genetics

Summary

Introduction

Insects make up a large proportion of the environment; it is not surprising that insects would be present in crime scenes. Insects recovered from the body can be used as a “clock” to determine the minimum postmortem interval (PMIMIN ), or the time since the body has been available to the insects, as most species in North America will only lay eggs or larvae on a resource if it is dead [2,3]. To estimate the PMIMIN , investigators should attempt to collect the oldest insect specimens present at the crime scene, and in some cases, these are pupae. Due to their lack of morphological characters, it is often difficult, if not impossible, to identify

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