African tsetse flies are not pleasant to encounter. Slightly larger than a horse-fly and very aggressive, they fly headlong toward their target at high speed, bounce off, and then search around for a suitable spot to tap it. If they are lucky enough to do so, they inflict a painful bite during which they drink almost their own body weight in blood. They are so devoted to blood that both sexes eschew any nutritionally supplementary foods (even female mosquitoes will drink nectar), and as a result, they have an uneasy alliance with three different symbiotic bacteria that can synthesize the vitamins their diet lacks. But their reproductive habits are downright mammalian. Single young suckle milk from their mothers inside a womb, before being evicted by a labor-like process.
We have just made a great advance in the war on these insects and the parasites that cause sleeping sickness that they carry in the sequencing of their genome, announced today in Science. I covered the story for National Geographic News; head on over there to read about the amazing things the genome revealed and to see the riveting video of a tsetse fly giving birth to a big fat larva. With 146 co-authors on the paper describing the geonome, one scientist I talked to aptly, I think, described the effort as "heroic".
I didn't have room in that story to include all that I learned while reporting it, especially some interesting details regarding their milk, so I thought I'd share those with you here.
Tsetse fly milk is incredibly similar to mammalian milk. It's a creamy emulsification of fats, proteins, and symbiotic bacteria that are essential for nutrition and immunity. The genome revealed that many of the tsetse milk proteins have evolved to function remarkably similarly to mammalian milk proteins like the caseins, which emulsify fats, or lactoferrin, which binds iron. The tsetse version of the latter, transferrin, binds iron to prevent bacteria from getting access to this vital nutrient and to aid larval development and nutrition.
Tsetse milk even transfers two of the three symbiotic bacteria that sustain tsetses and help develop their immune systems, which has analogies to the recent discovery that human milk transmits symbiotic gut bacteria to babies. One of the project scientists even mentioned to me that under the right conditions, the milk will even curdle like cow's milk, which inspired the revolting thought that it would be possible to make tsetse fly cheese (coming soon to a hipster bistro near you!).
Because drinking blood for a living also means a lot of drinking, they need proteins that can pump water out of their food. Ten of these proteins – the aquaporins – were found in tsetse flies, compared to six in mosquitoes and eight in the fruit fly Drosophila. The protein seems to have been co-opted for yet another purpose in tsetses – it's also abundant in tsetse milk glands, where it may be used to pump water into their milk.
The genome also revealed a small irony: traces of a virus associated with parasitic wasps. That suggests that tsetse flies are themselves or once were stalked by their own winged, stinging parasites.
To learn more, pop over to my story at National Geographic.