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Establishing Blow Fly Development and Sampling Procedures to Estimate Postmortem Intervals

NCJ Number
Date Published
91 pages
The most reliable biological indicator of time since death in cases where the body has decomposed is blow-fly development; this project developed datasets, models, and procedures for improving estimates of post-mortem interval (PMI) based on blow-fly development.
Because insects do not maintain constant body temperatures, their biological development is a function of time and temperature; therefore, having accurate models for describing temperature and blow-fly development is essential in producing accurate estimates of the PMI. To date, data on blow-fly development have been limited, and comprehensive growth models lacking. The current project used 66 sampling times in replicated laboratory studies in determining development requirements for each insect growth stage and transition between stages. The project developed improved degree-day (linear) models and curvilinear models for Lucilia sericata and Phormia regina. Work is underway to produce data for additional species. The project determined that stage transitions have normal distributions and can last from hours to days, depending on temperatures and stage. It was found that the third migratory stage does not show temperature-dependency above 17.5 degrees centigrade in either L. sericata or P. regina. This stage also showed the most variability in development time, but all stages had substantial variability, despite having little genetic variation. Field and laboratory observations confirmed that blow-fly feeding and stage transitions can occur at night and in darkness. Studies of anoxia tolerance with Calliphora vicina, Cochliomya macellaria, P. regina, and L. sericata manifested limited tolerance to anoxia with LT50 times between 1-10 hours; therefore, although larval movement in maggot masses could be associated with oxygen starvation, since LT50s are in the range of hours rather than minutes, it is more likely that movement is linked to thermoregulation. The project findings enable more precise methods for determining insect development and the associated PMI. Future research must develop comparable datasets on the development of other forensically important blow flies. 71 figures and 19 references

Date Published: January 1, 2014