Abstract
Introduction: In forensic entomology, dipterous larval specimens found feeding on decomposing corpses are usually preserved in a range of 70-95% ethanol before being subjected to minimum postmortem interval (mPMI) assessment. However, larval body size, which is commonly used to infer mPMI, can be affected by preservatives resulting miscalculation of estimation. This study compared the effect of ethanol concentrations on larval body and cephalopharyngeal skeleton, a potential substitute to estimate larval age for mPMI estimation. Methods: Experiments were conducted on homogenised colony of Chrysomya megacephala (Fabricius, 1794) (Diptera: Calliphoridae) third instar larvae reared in similar conditions. They were fixed with hot water (»80ºC) and preserved in 70% and 90% ethanol. After seven days in preservatives, larvae were measured for total body length from furthest part of the head to the last abdominal segment. Cephalopharyngeal skeleton was subsequently extracted from the body and measured based on morphometric landmarks on the pharyngeal sclerite. Centroid size of the cephalopharyngeal skeleton was also calculated based on the configuration of five morphometric landmarks. Results: In all four study replicates, pairwise comparisons with the original size indicated that larval body length was significantly affected by ethanol concentration (p<0.001) whilst only two of the study replicates showed cephalopharyngeal skeleton maintained its size when preserved in different ethanol concentration. Conclusion: Possible causes of variations are discussed herein with the results clearly indicated cephalopharyngeal skeleton should be considered as alternative growth parameter for mPMI estimation.
Highlights
In forensic entomology, dipterous larval specimens found feeding on decomposing corpses are usually preserved in a range of 70-95% ethanol before being subjected to minimum postmortem interval assessment
By considering the effect of preservatives on active feeding larvae based on morphological shape larval morphometry, we hypothesized that changes of cephalopharyngeal skeleton from the first cephalopharyngeal skeleton sizes would not react until third instar larvae
C. megacephala larvae used in each study replicate parameter to estimate mPMI, we suggest to conduct further investigation on the variations between using inter landmark distances and centroid size, before standardizing the geometrical landmarks to obtain centroid size for better estimation of cephalopharyngeal skeleton size [24, 25, 39]
Summary
Necrophagous insects found on human corpses can provide valuable input to the evaluation of minimum postmortem interval (mPMI) or the minimum time elapsed after death. Larval body skeleton dimensions from those studies were based on length of third instar Calliphora augur (Fabricius, the inter-landmark distances between mouth hook (MH). In a study using C. an alternative growth parameter to larval body length by vicina larvae preserved in 80% ethanol at -25oC, 6oC observing the reactions of cephalopharyngeal skeleton and 24oC for short (72 hours) and long (365 days) towards 70% ethanol for 0, 7 and 14 days [15]. 1830) active feeding larvae based on inter-landmark body lengths are inconsistent and vulnerable to killing distances established in the pharyngeal sclerite, i.e. between ADP-DC, ADP-VC and DC-VC [16]. By considering the effect of preservatives on active feeding larvae based on morphological shape larval morphometry, we hypothesized that changes of cephalopharyngeal skeleton from the first cephalopharyngeal skeleton sizes would not react until third instar larvae. Due to killing and preservation techniques, specific guideline to measure larval body length is currently
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