Size at emergence improves accuracy of age estimates in forensically-useful beetle Creophilus maxillosus L. (Staphylinidae)

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.

Development and validation of forensically useful growth models for Central European population of Creophilus maxillosus L. (Coleoptera: Staphylinidae)

“…Differences in development time between males and females of C. maxillosus were reported, however with no significant influence on the accuracy of age estimates using sex-specific as compared with general thermal summation models [7]. Creophilus maxillosus size at emergence was demonstrated to be useful for physiological age prediction and accordingly for the improvement of the age estimate accuracy in forensic entomology [47]. Moreover, it was found that the multiple measurement protocol affects the accuracy of insect age estimates using the resultant reference developmental data [8].…”

“…Thus, to get accurate insect age estimates, calculations should use developmental data for the local insect population [17,46]. Recently more attention has been paid to the Central European population of C. maxillosus [7,8,47]. Differences in development time between males and females of C. maxillosus were reported, however with no significant influence on the accuracy of age estimates using sex-specific as compared with general thermal summation models [7].…”

Sexual Dimorphism in Growth Rate and Gene Expression Throughout Immature Development in Wild Type Chrysomya rufifacies (Diptera: Calliphoridae) Macquart

“…As an example (Frątczak-Łagiewska and Matuszewski, 2018), determined that sex alone is not useful information for improving predictions of age in a forensically informative beetle. However, improvement did occur when knowledge of sex was combined with size at maturity (Matuszewski and Fratczak-Łagiewska, 2018). Similarly, one may imagine a gene is useful in predicting age, but only when the sex of the immature fly is known, due to differences in the way the sexes developmentally regulate a gene.…”

“…Furthermore, many fly species (the most important group of insects in forensic entomology) demonstrate dimorphism in both final adult size and/or development rate (Stillwell et al, 2010). Both of these factors may be important in the refinement and precision of insect age estimates (Blanckenhorn et al, 2007;Zuha and Omar, 2014;Blanckenhorn et al, 2015;Frątczak-Łagiewska and Matuszewski, 2018;Matuszewski and Fratczak-Łagiewska, 2018;Patrício Macedo et al, 2018). Concerns about sexual dimorphism in forensically important species have generally focused on organismal phenotypes; however, the same consideration must be made for molecular markers of fly age (e.g., gene expression), which are gaining traction as additional information that can (but may not always, see Smith and Cook, 2020) improve precision in insect age estimates for forensic purposes (Picard et al, 2013;Jonika et al, 2020).…”

An Evaluation of Differentially Spliced Genes as Markers of Sex for Forensic Entomology,,

“…Species without development time differences between the sexes would not be expected to impact casework results; however, other species may have large enough differences in development times between sexes to have an impact on minPMI estimates for casework. In beetles, the use of size and sex is useful in improving age estimates of forensically important species in at least one documented instance (25,26). While the impact of sexual dimorphism in development time is acknowledged (22,23,27), methods which have quantitatively evaluated the reliability to identify sex of immature Calliphoridae are lacking.…”