Abstract
Insects colonizing human or animal cadavers may be used to estimate post-mortem interval (PMI) usually by aging larvae or pupae sampled on a crime scene. The accuracy of insect age estimates in a forensic context is reduced by large intraspecific variation in insect development time. Here we test the concept that insect size at emergence may be used to predict insect physiological age and accordingly to improve the accuracy of age estimates in forensic entomology. Using results of laboratory study on development of forensically-useful beetle Creophilus maxillosus (Linnaeus, 1758) (Staphylinidae) we demonstrate that its physiological age at emergence [i.e. thermal summation value (K) needed for emergence] fall with an increase of beetle size. In the validation study it was found that K estimated based on the adult insect size was significantly closer to the true K as compared to K from the general thermal summation model. Using beetle length at emergence as a predictor variable and male or female specific model regressing K against beetle length gave the most accurate predictions of age. These results demonstrate that size of C. maxillosus at emergence improves accuracy of age estimates in a forensic context.
Highlights
There are several methods for post-mortem interval (PMI) estimation based on insect evidence
Recent study with forensically-useful beetle C. maxillosus did not support the use of sex-specific developmental models in forensic entomology, as despite significant differences in development time between males and females of C. maxillosus, there was no gain in the accuracy of age estimates using sex-specific developmental models[24]
We test the concept that insect size at emergence is a good predictor for development time and it may be used to improve the accuracy of insect age estimates in forensic entomology
Summary
There are several methods for post-mortem interval (PMI) estimation based on insect evidence. We predict that 1) thermal summation value (K) needed by individual beetles of C. maxillosus to reach the adult stage is related to the size of beetles at emergence, 2) using the insect size to estimate K may significantly improve the accuracy of insect age estimates in forensic entomology, and 3) the relationship between insect size and K needed for emergence will be represented with higher accuracy by separate models for males and females than the pooled model To test these predictions we used results of developmental experiment, in which immature C. maxillosus were reared using standardized laboratory protocol, at different constant temperatures and optimal food conditions, with monitoring of development time and determination of insect size and sex at emergence
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