The tsetse fly (Genus Glossina) is notable for two things: it carries parasites called trypanosomes, which cause sleeping sickness in humans and nagana in cattle in sub-Saharan Africa; and it gives birth to live young. Attempts to control these devastating diseases have focused on controlling the insect vectors, particularly because they breed slowly raising only one larva at a time.
Most flies, like the common house fly, lay large numbers of eggs that hatch into larvae (maggots) that eventually form a pupa and emerge as an adult fly. Instead, the female tsetse fly incubates the larva within herself, even nourishing it with a kind of milk. When the larva is almost ready to pupate, it squeezes its way out of the mother and buries itself in some soil from which it will emerge as an adult.
(For a video of a tsetse fly giving birth, look here.)
Clearly, there’s something pretty unusual about the genital tract of a female tsetse fly. Now researchers led by Geoffrey Attardo, assistant professor at the UC Davis Department of Entomology and Nematology, working with the Advanced Light Source at Lawrence Berkeley Laboratory, have produced a micro-CT scan of the insides of a tsetse fly in stunning detail.
The technique uses high-energy X-rays from the synchrotron at the Advanced Light Source to scan a series of layers through biological tissue. These slices can then be assembled into a 3D image. By using a refinement called phase contrast micro-CT, the team were able to distinguish soft tissues within the insect’s abdomen.
The new images reveal the modifications necessary for the fly to consume large blood meals and brood a single larva nearly as big as itself.
“The use of pcMicroCT provides unprecedented opportunities for examination and discovery of internal morphological features not possible with traditional microscopy techniques,” the authors wrote. It should open up new ways to study the biology of tsetse flies and other insects.
“This is our first step,” Attardo said. “The next step is to implement deep learning algorithms to have AI segment out the tissues rather than doing it semi-manually.”
A preprint describing the work is available at BiorXiv.org. Additional authors are Nicole Tam, Lindsey Mack, Xavier Zahnle and Joceline Arguellez at UC Davis; Dilworth Parkinson, LBL; Peter Takac, Slovak Academy of Sciences, Slovakia (where the flies were bred) and Anna Rodolfa Malacrida, University of Pavia, Italy.
The work was supported by grants from the NIH and the Slovak Research and Development Agency. The Advanced Light Source is funded by the U.S. Department of Energy.
Three-dimensional analysis and visualization of morphological adaptations associated with viviparity in the Tsetse fly (Glossina morsitans) BiorXiv.org (preprint server)