Newswise – Researchers from the University of Bristol and Stellenbosch University in South Africa have found that the fertility of both female and male tsetse flies is affected by a single outbreak of heat.

The effects of a single heat wave were felt even by the offspring of heat-exposed parents, with more daughters than sons being born.

The study published today in Proceedings of the Royal Society Bhelps explain why tsetse flies are declining in some parts of their range in Africa and has important implications for the diseases they spread, particularly sleeping sickness in humans and Nagana in cattle.

Lead author Dr. Hester Weaving from Bristol Faculty of Biological Sciences said: “A single heat wave affected both male and female fertility of the disease-carrying tsetse flies, causing populations to decline.”

“Ultimately, heat waves can drive insect biodiversity loss through both direct death and fertility losses, which is concerning given the increasing frequency and intensity of heat waves due to ongoing climate change.”

Scientists know that many animals’ fertility is affected at temperatures less extreme than those that kill them. In some cases, heat can cause animals to become completely sterile, meaning they can no longer produce offspring. In general, male fertility tends to be more temperature sensitive than female fertility, so the current results are surprising.

The team conducted laboratory experiments using water baths in Bristol to mimic a heatwave event. To find out whether females or males were more sensitive to heat waves, they exposed them to the heat separately and then mated them with unexposed members of the opposite sex. They measured how many offspring the flies produced and how many deaths occurred six weeks after the heat wave.

Dr. Weaving said: “We studied this in tsetse flies, which transmit sleeping sickness to humans, livestock and wildlife in sub-Saharan Africa.”

“They are fascinating insects because they each develop a single egg and feed it a milk-like substance as a larva in the uterus. The mother then gives birth to the larva, which can weigh the same as herself.”

The researchers have shown that male fertility is not more sensitive to heat in all insects.

Lead author of the study, Dr. Sinead English, said: “Our study provides important insights into how climate change will affect disease-carrying insects. We cannot assume that the patterns in tsetse flies correspond to those in better-studied laboratory systems such as seed beetles or fruit flies.”

More insect species should now be measured to see whether this result is widespread among other insect species and has important implications for their global distribution in the face of climate change.


“Heat waves affect the fecundity of the viviparous tsetse fly” by Hester Weaving, John S. Terblanche and Sinead English in Proceedings of the Royal Society B

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