Visualising fat reserves in an insect: A method using X-ray micro-computerised tomography of the Common Wasp (Vespula vulgaris)

The Common Wasp, Vespula vulgaris (Hymenoptera: Vespidae), has an annual nest cycle with new colonies initiated by over-wintered queens. Survival of adult queen wasps through winter dormancy is enabled through the deposition of substantial quantities of triglycerides in fat bodies. Worker (and male) wasps lack these fat reserves. By comparing micro-CT scans of workers, pre-hibernation queens and post-hibernation queens, we demonstrate that it is possible to semi-quantitatively measure fat reserves using arbitrary X-ray attenuation ranges. Venom in the venom gland of the queen wasps, has a significantly lower X-ray attenuation value than the triglyceride-rich fat bodies. This may be due to its content of low molecular weight volatile pheromones in addition to its other known constituents. We also demonstrate the utility of micro-CT for visualising a range of physiological and anatomical features of insects. This non-destructive method for measuring fat reserves can be used on appropriately preserved or freshly collected insect specimens.