Virtual forensic entomology: improving estimates of minimum post-mortem interval with 3D micro-computed tomography.

Area of Science:

• Forensic Entomology
• Developmental Biology
• Imaging Technology

Background:

• Metamorphosis involves significant morphological changes.
• Accurate insect age estimation is crucial in forensic investigations.
• Micro-computed tomography (micro-CT) offers high-resolution imaging capabilities.

Purpose of the Study:

• To evaluate micro-CT for characterizing morphological changes during Calliphora vicina metamorphosis.
• To determine optimal staining methods for micro-CT contrast in blowfly pupae.
• To assess the utility of micro-CT derived data for estimating pupal age.

Main Methods:

• Calliphora vicina pupae were sampled at four developmental stages (quarters) post-pupariation at 23°C.
• Pupae were preserved in 80% ethanol and subjected to different staining protocols (iodine, radiopaque dye, unstained control).
• Micro-CT scans were acquired at 17.2 μm resolution to visualize internal and external morphology.

Main Results:

• Seven-day iodine staining yielded the best contrast for micro-CT imaging.
• Internal and external morphological features of developing pharate adults were discernible at all sampled ages.
• Combined internal and external morphological data improved age estimation accuracy and precision compared to external features alone.

Conclusions:

• Micro-CT is a powerful tool for detailed morphological analysis of insect metamorphosis.
• This technique enables precise age estimation of blowfly pupae, aiding forensic investigations.
• The described method can establish a minimum post-mortem interval when pupae are the oldest insect evidence.