Many common insects including mosquitoes and flies primarily live on a liquid diet. Being small in size, pumping fluids poses a unique challenge insects need to solve. As the size of the creatures scales down to microscopic regimes, viscous forces dominate and it requires significant energy to pump fluids. For a given liquid diet such as nectar, viscosity of the fluid increases exponentially to the sugar concentration while the energy extracted from the solution only increases linearly with the amount of sugar present, presenting a severe constraint for pumping mechanism for insect feeding.1 

Here, we directly visualize feeding in the common house fly, Musca domestica (Fig. 1(a)) via absorption X-ray microscopy. A starved fly is fed sugar solution of a known viscosity and sugar concentration, while fluid flow through the pump is observed in real time. A small amount of contrast agent is added to the feeding solution to provide a clear trace of fluid transport during a pumping cycle (Fig. 1(a) inset). Various X-ray imaging protocols were developed to allow for high resolution imaging using a simple table-top X-ray source. The pulsatile nature of the cibarial pump (Fig. 1(b)) in flies is depicted in Fig. 1(c). Via direct visualization of fluid flow during a single feeding stroke in flies, fluid-structure coupling of the pump geometry is revealed.

We gratefully acknowledge financial support for M.P. from Harvard Society of Fellows Milton Award and Terman Fellowship from Stanford University. We thank MIT Center for Bits and Atoms for laboratory space and U.S. Army Research Office W911NF-08-1-0254 for equipment grant. The authors gratefully acknowledge the kind assistance of BrijPal Singh for research material collection.

J. G.
T. L.
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On the mechanics and energetics of nectar feeding in butterflies
J. Theor. Biol.