Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) development by landmark-based geometric morphometrics of cephalopharyngeal skeleton: a preliminary assessment for forensic entomology application

Li-Xuan Sim,Raja M Zuha

doi:10.1186/s41935-019-0158-y

Li-Xuan Sim, Raja M Zuha

Open Access

https://doi.org/10.1186/s41935-019-0158-y

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Abstract

BackgroundConsidering the practicality of geometric morphometrics which could discriminate insect species, this application was extended to the analysis of blow fly larval growth based on cephalopharyngeal skeleton. In forensic entomology, cephalopharyngeal skeleton plays a crucial role in species identification but the morphometric information of this part is scarce. In this study, Chrysomya megacephala (Fabricius, 1794) was reared in two study replicates in natural conditions and samplings were conducted at fixed daily intervals. Cephalopharyngeal skeletons were removed from larvae and mounted on glass slides. Images were obtained from the specimens; digitized and geometric morphometric analysis on C. megacephala cephalopharyngeal skeletons was performed with MorphoJ software based on the ordination of five landmarks. The assessments of this analysis were based on centroid size measurements, visualization on the landmarks displacements, classification of the relative landmarks by using canonical variate analysis, and ontogenetic allometry determination.FindingsCentroid size was strongly correlated with developmental time (p < 0.05) and significantly different between daily intervals (p < 0.05). Ontogenetic allometric effect based on multivariate regression on Procrustes coordinates and centroid size was significant (p < 0.0001), indicating that shape was influenced by growth (60.3%). Disposition occurred on all landmarks during development and was further discriminated based on age groups.ConclusionsOther than discriminating between species, geometric morphometrics was found to be practical to visualize larval growth based on cephalopharyngeal skeletons which can be useful in forensic entomology.

Highlights

In forensic entomology, the age of dipterous larvae, found feeding on decomposing human remains, can be used to estimate minimum post mortem interval
Other than discriminating between species, geometric morphometrics was found to be practical to visualize larval growth based on cephalopharyngeal skeletons which can be useful in forensic entomology
In order to determine whether centroid size varies significantly at different sampling intervals, one-way between-group analysis of variance (ANOVA) was performed followed by Games-Howell post hoc analysis for non-homogeneous variances data set

Summary

Introduction

In forensic entomology, the age of dipterous larvae, found feeding on decomposing human remains, can be used to estimate minimum post mortem interval (mPMI). In Calliphoridae larvae, cephalopharyngeal skeleton is the invaginating mouthparts in the cephalic region of the larva, consisting of pharyngeal sclerites and mandibles which are used to facilitate food intake (Teskey 1981) These structures provide vital diagnostic features to identify blow fly species of forensic importance (Greenberg and Kunich 2002) but apparently, the morphometric information of cephalopharyngeal skeleton is still lacking. Images were obtained from the specimens; digitized and geometric morphometric analysis on C. megacephala cephalopharyngeal skeletons was performed with MorphoJ software based on the ordination of five landmarks. The assessments of this analysis were based on centroid size measurements, visualization on the landmarks displacements, classification of the relative landmarks by using canonical variate analysis, and ontogenetic allometry determination

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