Generating More Precise Post Mortem Interval Estimates With Entomological Evidence: Reliable Patterns of Gene Expression Throughout Calliphorid Larval and Pupal Development

Insects, especially flies (Diptera), can be important tools in forensic investigation of deaths, as many insect species eat, breed on, or are otherwise associated with decaying remains. Calliphoridae, Sarcophagidae, and Muscidae flies are the most useful insects in this type of investigation because they are capable of locating and ovipositing (egg laying) on a corpse within hours or even minutes of death. Based on an approximation of the age of immature flies (larvae or pupae) associated with the body, an estimate of post mortem interval can be made. Presently, length measurements of fly larvae or qualitative analysis of the color of pupae are the most common estimators of immature fly age. The former is useful in age estimates as fly larvae increase linearly in length throughout most of their immature life cycle. However, near the end of larval development flies shrink as they prepare to pupate, meaning age estimates based on length can be inaccurate. Likewise, it is difficult for investigating forensic entomologists to age pupae due to a dearth of information on pupal development. The goal of this DNA Research and Development project is to increase the accuracy of entomological evidence used to estimate postmortem interval by focusing on developmentally regulated genes in forensically useful species. Michigan State University's research will be based on determining relative RNA levels of genes that are finely regulated during developmental stages of flies. By examining a series of genes, some of which are up-regulated at certain stages, while others are down-regulated, it should be possible to determine the age of an immature fly with improved accuracy.

ca/ncf