For years, insect populations have been dropping worldwide without a clear explanation. A new paper suggests male infertility is at least one factor behind that decline, as warmer-than-usual temperatures take a disproportionate toll on males of some insect species.

After a lab-simulated heat wave, researchers from England’s University of East Anglia found that male flour beetles produced vastly less sperm. But they also found that the damage wasn’t confined to the males. Sperm inside a female’s reproductive tract became less viable and the sons of the males that endured the hotter temperature became less fertile, too.

Matt Gage, an evolutionary ecologist who led the work published Tuesday in Nature Communications, said he was surprised by the findings, and by how quickly male fertility plummeted.

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It’s long been known that heat can affect sperm quality in mammals. “There’s a good reason the testes are outside the body,” noted Dr. Gage, adding that this keeps the sperm 6 to 10 degrees cooler than body temperature.