The fertility of both female and male tsetse flies is affected by a single burst of hot weather, researchers at the University of Bristol and Stellenbosch University in South Africa have found. The effects of a single heatwave were even felt in the offspring of heat exposed parents, with more daughters being born than sons. Ultimately, heatwaves can drive insect biodiversity loss through both direct death and fertility losses, which is concerning given that heatwaves are increasing in frequency and intensity due to ongoing climate change.

Scientists know that in a lot of animals, fertility is damaged at less extreme temperatures than those which kill them. In some cases, animals can become entirely sterile in response to heat, making them incapable of producing offspring. Generally, male fertility tends to be more temperature sensitive than female fertility, so the current results are surprising. The team performed experiments in the lab using water baths at Bristol to mimic a heatwave event. They measured how many offspring the flies produced and deaths over six weeks after the heatwave. They looked at this in tsetse flies which spread the disease sleeping sickness in sub-Saharan Africa to humans, livestock and wild animals.

The researchers have shown that male fertility being more heat sensitive is not common to all insects. Senior author on the study, Dr Sinead English, said: "Our study provides important insights to how climate change will affect disease-carrying insects. We can't assume that patterns in tsetse match those found in better-studied lab systems like seed beetles or fruit flies." Now further insect species should be measured to see if this result is widespread among other insect species with important implications on their global distributions in the face of climate change.