Metrological framework for selecting morphological characters to identify species and estimate developmental maturity of forensically significant insect specimens

Abstract

Accurate age estimates of immature necrophagous insects associated with a human or animal body can provide evidence of how long the body has been dead. These estimates are based on species-specific details of the insects’ aging processes, and therefore require accurate species identification and developmental stage estimation. Many professionals who produce or use identified organisms as forensic evidence have little training in taxonomy or metrology, and appreciate the availability of formalized principles and standards for biological identification. Taxonomic identifications are usually most readily and economically made using categorical and qualitative morphological characters, but it may be necessary to use less convenient and potentially more ambiguous characters that are continuous and quantitative if two candidate species are closely related, or if identifying developmental stages within a species. Characters should be selected by criteria such as taxonomic specificity and metrological repeatability and relative error . We propose such a hierarchical framework, critique various measurements of immature insects, and suggest some standard approaches to determine the reliability of organismal identifications and measurements in estimating postmortem intervals. Relevant criteria for good characters include high repeatability (including low scope for ambiguity or parallax effects), pronounced discreteness, and small relative error in measurements. These same principles apply to individuation of unique objects in general. Key points Metrological rigour can increase in forensic entomology by selecting measurements based on their metrological qualities. Selection of high-quality features for morphological identification of organisms should consider these criteria: (1) pronounced discreteness of features (minimising group overlap or maximizing interval); (2) high repeatability of assessment (such as symmetrical width rather than asymmetrical length); (3) small relative error in measurement (selecting the physically largest continuous rigid feature for measurement). These metrological principles also apply to individuation of unique objects in general.

Calibrating insect age at eclosion by size in a gregarious carrion beetle Thanatophilus sinuatus (Staphylinidae: Silphinae)

“…Another intriguing aspect of the current study is the better performance of width measurements over length measurements. Similar differences were reported by Midgley and Villet (2021) while testing the usefulness of size measurements to identify the species or to classify the larval instar. Further studies are necessary, with different species, to test whether this is the universal pattern.…”

“…The body mass of the adult beetles was weighed using the analytical balance (AS 82/220.R2, Radwag™, Poland). We measured (following general recommendations by Midgley & Villet, 2021) the length and width of the pronotum and the length of elytra (Figure 1). Width of the pronotum was measured in its upper part (the distance between frontal protrusions of the pronotum) and lower part (the distance between the left and right extreme points of the pronotum) (Figure 1).…”

Molecular identification of Hymenopteran insects collected by using Malaise traps from Hazarganji Chiltan National Park Quetta, Pakistan

“…To address this issue, the use of molecular techniques specifically DNA Barcoding have been employed to enable large-scale assessments of biodiversity [ 29 – 31 ]. The mitochondrial cytochrome c oxidase subunit 1 ( cox1 ) gene is most commonly used as a genetic marker due to the presence of conserved region [ 26 , 32 ] allowing for discrimination between various groups or biotypes or ‘cryptic species’ in a single species [ 33 , 34 ]. The use of Barcode Index Numbers (BINs) in these studies boundaries by comprehensively presenting species diversity [ 35 , 36 ].…”

“…Traditional morphological based approach to insect taxonomy has long been established as an effective means of specie description and identification [17]. However, these methods are challenged [18,19,25] by a variety of juvenile life stages of insects, individuals with fluctuating phenotypes and cryptic species that complicate distinct identification [18,[26][27][28][29][30]. To address this issue, the use of molecular techniques specifically DNA Barcoding have been employed to enable large-scale assessments of biodiversity [29][30][31].…”

Temporal Dynamics and DNA Barcoding of Hymenoptera from Juniper Forest Ecosystem

“…Traditional morphological classification methods of insects remain relevant in taxonomy for describing the diversity of insects [23]. However, identifying species through this morphological method using a microscope proves challenging because it requires indepth knowledge [24,25] to differentiate closely related species [26].…”