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Friday, May 4, 2012

The lactating tsetse fly

Here’s something I did not know: tsetse flies (genus Glossina) nurse their young. Okay, it’s not exactly nursing, but the mothers do secrete a milk-like substance that they feed to their larvae. Not only that, but they nurture their young internally in a uterus. Those of you with training in entomology may be smugly nodding, but the rest of us find this amazing.

Pinned tsetse fly specimen from the American Museum of Natural History, New York.
Photographed 7/8/2005 by Tam Nguyen.

Tsetse flies are better known as the blood-sucking scourges of sub-Saharan Africa that are responsible for the spread of numerous diseases, including Elephantiasis and sleeping sickness. Up to 300,000 people are killed each year by tsetse-transmitted illnesses. 

Tsetse flies practice ‘Adenotrophic viviparity’. Literally ‘gland-fed live-birth’, this means that the fertilized egg (there’s only one at a time) is retained within the mother’s uterus where it is fed a milk-like solution from special glands. It’s not until the third larval stage (3rd instar) that the offspring ventures out into the world. It quickly pupates and emerges some weeks later as an adult fly.

All the energy required for growth and metamorphosis comes solely from the mother, which she in turn gets from her blood meals. In other words, all that affliction is caused by a fly in the pursuit of motherhood. And after all, it’s not her fault she’s transmitting trypanosomes with each bite.

The similarity between the milk of these insects and that of mammals is uncanny. For example, Joshua Benoit of Yale and his colleagues were able to adversely affect the growth of tsetse larvae by blocking the production of a key enzyme. Humans have a similar enzyme, the lack of which causes a severe neurodegenerative disorder known as Niemann-Pick Disease. In other experiments led by Geoffrey Attardo of Yale, the production of the tsetse milk lipids could be disrupted, leading to the loss of 80% of the larvae. Again, similar pathways exist in mammals.

I find the idea that flies and mammals are so alike to be fascinating, though I suspect the researchers involved are more interested in finding ways to eliminate the threat of these pathogen-carriers, which is fair enough. 

You can watch the tsetse life cycle in the videos below. Don't miss the 'birth' of the larvae, starting at 4:20 in the first video and continuing in the second.

If that's not enough tsetse action for you, check out this x-ray footage of flies mating.