Investigating upper thermal limits of forensically important blow flies to improve testimony in forensic entomology

As submitted by the proposer:
Insect evidence can provide valuable information during death investigations. Since carrion-feeding flies often colonize remains soon after death, estimates of insect age derived from immature insects collected from a body can provide information regarding the timing of a death, including the postmortem interval itself if some assumptions are satisfied. Typically, this is done by evaluating the evidence in light of assumed developmental data sets, assumed temperature exposures, and assumed models of thermal responses of development to temperature – usually through the use of accumulated degree models. Thus, predictions of insect age for forensic casework rely on assumptions regarding the thermal responses of fly behavior and development.

Consequently, there are instances where these assumptions regarding insect development result in inaccurate and less precise conclusions with regards to casework. One assumption in particular is the identification of an upper temperature threshold experienced by the insects that can kill or inhibit development, locomotion, or egg-laying behavior. To date, these temperatures are not known for forensically important insects for many of the species of forensic interest. Thus, the impact of this assumption on conclusions drawn by forensic entomologists is not known. To improve forensic casework with entomological evidence in such instances, we propose to do a series of experiments to identify the upper thermal limits of two forensically important flies that are common throughout the United States and likely to be collected as evidence in cases where assumptions about upper thermal limits of these flies are important but not considered.

Accordingly, we will identify temperatures at which flies are paralyzed or killed by heat, will not oviposit, cannot develop efficiently with additional heat, and the degree to which adult and larval flies of forensic importance can regulate their body temperatures through behavior. In addition, we propose to investigate the impact of maternal heat stress on subsequent development of her offspring. In all cases, the knowledge generated by this project will have an immediate impact on approaches applied in casework in states that encounter high temperatures during the summer sufficient to negatively impact flies of forensic importance, thereby improving the implementation of forensic entomology in such cases. Such efforts will result in greater accuracy and precision when estimating the time of colonization of human remains.

Note: This project contains a research and/or development component, as defined in applicable law.

ca/ncf