Quantifying pteridines in the heads of blow flies (Diptera: Calliphoridae): Application for forensic entomology

- This is the first study to quantify pteridines in Nearctic populations of blow flies.
- Pteridines can be used to estimate adult blow fly age at temperatures above 15 °C.
- This technique can be used in cases where decomposing remains are found indoors.

In forensic cases involving entomological evidence, establishing the postcolonization interval (post-CI) is a critical component of the investigation. Traditional methods of estimating the post-CI rely on estimating the age of immature blow flies (Diptera: Calliphoridae) collected from remains. However, in cases of delayed discovery (e.g., when remains are located indoors), these insects may have completed their development and be present in the environment as adults. Adult fly collections are often ignored in cases of advanced decomposition because of a presumed little relevance to the investigation; herein we present information on how these insects can be of value. In this study we applied an age-grading technique to estimate the age of adults of Chrysomya megacephala (Fabricius), Cochliomyia macellaria (Fabricius), and Phormia regina (Meigen), based on the temperature-dependent accumulation of pteridines in the compound eyes, when reared at temperatures ranging from 5 to 35 °C. Age could be estimated for all species*sex*rearing temperature combinations (mean r2 ± SE: 0.90 ± 0.01) for all but P. regina reared at 5.4 °C. These models can be used to increase the precision of post-CI estimates for remains found indoors, and the high r2 values of 22 of the 24 regression equations indicates that this is a valid method for estimating the age of adult blow flies at temperatures ≥15 °C.