Developmental variation among Cochliomyia macellaria Fabricius (Diptera: Calliphoridae) populations from three ecoregions of Texas, USA.

Forensic entomologists rely on published developmental datasets to estimate the age of insects developing on human remains. Currently, these datasets only represent populations of targeted insects from specific locations. However, recent data indicate that populations can exhibit genetic variation in their development, including signatures of local adaptation demonstrated by regionally distinct plastic responses to their environments. In this study, three geographically distinct populations of the secondary screwworm, Cochliomyia macellaria Fabricius (Diptera: Calliphoridae; College Station, Longview, and San Marcos, TX, USA), a common blow fly collected from human remains in the southern USA, were reared in two distinct environments (cool 21 °C, 65 % relative humidity (RH); and warm 31 °C, 70 % RH) over 2 years (2011 and 2012) in order to determine differences in development time and mass. Significant differences in immature and pupal development time, as well as pupal mass, were shown to exist among strains derived from different populations and years. For immature development times, there was evidence of only an environmental effect on phenotype, while genotype by environment interactions was observed in pupal development times and pupal mass. College Station and San Marcos populations exhibited faster pupal development and smaller pupal sizes in the cooler environment relative to the Longview population, but showed an opposite trend in the warm environment. Rank order for College Station and Longview populations was reversed across years. Failure to take genetic variation into consideration when making such estimates can lead to unanticipated error and bias. These results indicate that genetics will have little impact on error when working with Texas genotypes of C. macellaria at ~30 °C and 70 % RH, but will have a more meaningful impact on error in postmortem interval estimates with this species in cooler, drier environments.