Tsetse flies are vectors of trypanosomes that cause human and animal disease in sub-Saharan Africa. Historically, these flies and the trypanosomes they transmit have had very detrimental effects on the health and development of this region. Despite more than a century of tsetse research, volatile sex pheromones have not been identified.

In a new study, Yale scientists identified a volatile pheromone emitted by the tsetse fly. The finding provides new information about how flies communicate with each other and could lead to new approaches to managing fly populations and the dangerous diseases they transmit.

When the tsetse flies bite humans or animals, they transmit parasites called African trypanosomes that spread diseases such as African sleeping sickness, which can be deadly to humans, and nagana, a disease that affects cattle and other animals.

John Carlson, the Eugene Higgins Professor of Molecular, Cellular, and Developmental Biology in the Yale School of Arts and Sciences and senior study author, said: “African sleeping sickness is a terrible disease that is difficult to treat. Our immune system has a hard time clearing trypanosomes and most of the drugs we have to kill them are toxic. And nagana, which affects livestock, has had terrible economic consequences in the region.”

Using their pheromones, specifically volatile pheromones, or pheromones that act over distances rather than through direct contact, to attract and trap the insects has been proposed as a method of preventing the spread of tsetse flies.

The Yale research team selected tsetse flies from the species G. morsitans and placed them in a liquid to collect all the compounds they could produce to find volatile pheromones that could be used for this purpose. Scientists then subjected those extracts to a gas chromatograph mass spectrometer, a tool that can isolate certain molecules from a mixed mixture.

Scientists found several chemicals that had never been reported before, including three that elicited responses from tsetse flies. One in particular, a chemical called methyl palmitoleate (MPO), had the strongest effects. Scientists found that MPO attracted male tsetse flies, caused them to stop and stay in place for a while, and had an aphrodisiac effect in a battery of tests.

A drop of liquid containing MPO lured male tsetse flies to knots in yarn that only resembled flies and to females of another tsetse fly species with which they would not normally interact.

The scientists next examined whether neurons on the flies’ antennae responded to MPO to understand how MPO mediated behavior. They detected a subset of olfactory neurons on the antennae and found that these neurons fired more often in response to the pheromone.

Scientists noted, “Together, the findings indicate that MPO is a tsetse fly attractant and may therefore be useful in slowing the spread of disease.”

carlson said, “Now we’ve found this pheromone that can be used with the host’s scents. Especially since MPO attracts the flies and causes them to freeze where they are.”

“While animal odors benefit from attracting tsetse flies over long distances, they tend to fade quickly. MPO works at shorter distances but is effective for longer periods.”

“MPO could be another tool in the toolbox when it comes to combating tsetse flies and the diseases they spread.”

Scientists are now testing whether MPO is useful in real-world traps, not just a lab setting. They also look forward to understanding why Tsetse flies infected with trypanosomes emit an entirely different set of chemicals and how that affects communication with flies.

Magazine reference:

  1. Shimaa AM Ebrahim et al. A volatile sex attractant of tsetse flies. Science. DOI: 10.1126/science.ade1877