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An X-ray film of a fly pupa undergoing metamorphosis has captured in minute-by-minute detail the most dramatic part of the reorganisation process.
The research by Natural History Museum scientists examines the metamorphosis of the bluebottle blow fly Calliphora vicina, which cannot usually be seen because it occurs within an opaque brown structure, the puparium.
Although the whole pupation stage lasts about ten days in the summer, there is a 1.25 hour period in which the organism visibly transforms from a maggot shape to an adult-like structure with a body, legs and head.
In the first 24 hours of metamorphosis, much of the larval structures of the maggot degenerate. The dramatic change then begins as an air bubble escapes from the pupa into the puparium, allowing space for the head to appear and for the adult framework to erupt from special cells within the insect.
‘This very dramatic change shows the moment when the framework for the fly is produced,’ says lead author and forensic entomologist Martin Hall. ‘The rest of the pupation period is then spent fitting it out.’
The video, produced in the Museum’s Imaging and Analysis Centre, was made by taking X-rays of the pupa at one and two-minute intervals, capturing the process in greater detail than has been done previously.
Forensic entomologists such as Hall are interested in the lifecycle of C. vicina because they can help estimate how long someone has been dead for. The flies are one of the first organisms to find a dead body, which they then lay their eggs on. The resulting maggots and pupae then develop at predictable rates according to the temperature, so the time when the flies first discovered the body can be calculated. This gives a minimum time since death.
The new research will help determine the age of pupae found at a crime scene more accurately, thus improving the estimated time of death.
For more on this story and a link to the video, click here.
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Images and video: Please download from here and credit: © The Trustees of the NHM, London
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Full paper Hall MJR, Simonsen TJ, Martín-Vega D. 2017 The ‘dance’ of life: visualizing metamorphosis during pupation in the blowfly Calliphora vicina by X-ray video imaging and micro-computed tomography. R.Soc.opensci.4:160699. http://dx.doi.org/10.1098/rsos.160699
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