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

Abstract

Background: Considering 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. Findings: Centroid 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. Conclusions: 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.

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

“…However, typically, they do not drastically differ between instars within a species, which makes quantitative measures of maturity necessary. The shape or colour of a feature can be quantitatively described by morphometrics [ 33 , 34 ] or spectrometry, respectively. Pupal development does not progress through discrete stages, but the development of certain features (such as seta formation or setal pigmentation) can be treated as discrete developmental landmarks at sufficiently coarse time scales and continuous developmental processes at finer temporal resolutions [ 3 ].…”

Random forests for predicting species identity of forensically important blow flies (Diptera: Calliphoridae) and flesh flies (Diptera: Sarcophagidae) using geometric morphometric data: Proof of concept

“…Recent work on the application of geometric morphometrics to wing shape analysis of species from the Sarcophagidae and the Calliphoridae family showed that wing shape variation was reliable for classifying Chrysomya species [37] and even distinguishing between sexes of the same species [38]. Further application to cephalopharyngeal skeleton shape of fly larvae is also possible [39,40].…”

CEPHALOPHARYNGEAL SKELETONS OF Chrysomya megacephala (Fabricius, 1794) (DIPTERA: CALLIPHORIDAE) THIRD INSTAR LARVAE DISPLAYED RESISTANCE TO HOT-WATER KILLING METHOD – IMPLICATIONS IN FORENSIC ENTOMOLOGY PRACTICE

“…Studying the efficacy of the cephalopharyngeal skeleton as a growth parameter is therefore necessary as in the later studies recorded it grew proportionally with larval body size during active feeding stage (Eliza & Zuha, 2018;Sim & Zuha, 2019). The current study compared the effect of hot water and direct killing by immersion in 70% ethanol on the cephalopharyngeal skeleton and total body size of third instar Chrysomya megacephala (Fabricius, 1786) larvae, a forensically important blowfly in Malaysia, Thailand, and the rest of the world (Lee et al, 2004;Sukontason et al, 2008;Thevan et al, 2010;Badenhorst & Villet, 2018).…”

“…The internal tissues surrounding the cephalopharyngeal skeleton were carefully removed in 10% KOH and subsequently transferred into 10% acetic acid for 10 min. Cephalopharyngeal skeleton was then soaked in 70% ethanol for 20 min before they were mounted onto a glass slide in lateral position using Berlese fluid and covered by a 6 mm round coverslip (Sim & Zuha, 2019). Measurements of the cephalopharyngeal skeleton were conducted immediately after the mounting process based on inter landmark distances between anterodorsal process (tip of the dorsal bridge) to dorsal cornu (ADP-DC), the anterodorsal process to ventral cornu (ADP-VC), and dorsal cornu to ventral cornu (DC-VC) (Nateeworanart et al, 2010;Nuñez & Liria, 2016;Rabbani & Zuha, 2017) (Figure 1).…”

“…Most importantly, results from the current study suggesting that cephalopharyngeal skeletons can be used as an alternative growth parameter to estimate larval age after larval body length was found to be affected by various practical factors. For example, Sim & Zuha (2019) showed that the cephalopharyngeal skeleton size of C. megacephala had a linear growth pattern during the active feeding period. Likewise, in other calliphorid species, the cephalopharyngeal skeleton could show positive trajectories throughout larval development as observed in H. violacea (Rabbani & Zuha, 2017) and Hemipyrellia ligurriens (Wiedemann, 1830) (Eliza & Zuha, 2018).…”