Larvae of Diptera are used routinely in forensic entomology to estimate accurately the post mortem interval. These applications require a detailed understanding of insect growth rates and insect succession profiles under different climactic conditions and geographical locations. There may be times when larvae may have been removed from a single food source or the corpse has been moved from one location to another, confounding the interpretation of the entomological data. The authors report here a study that evaluates the time period during which a food source can be detected in larvae of Protophormia terraenovae. The study could detect the food source (pork or chicken liver) that larvae had ingested from early second instar to late third instar larvae. No detection was possible in pupae or adults. When larvae were transferred from one food source to another, the primary source was detectable for only 8-12 hours after transfer, whereas it was detectable for 12 hours in starved larvae. In most studies that use insects to estimate PMI, investigators collect larvae directly from the corpse. In cases where there have been significant disturbances, investigators must understand the changes in insect dieting and development that may take place. Figure, tables, and references (Published Abstract)