Thirty-two million is a number that makes most people uncomfortable when it refers to mosquitoes. Yet that is precisely how many sterilised male insects Alphabet — the parent company of Google — has asked the United States federal government for permission to release across California and Florida. The programme, run by Alphabet's Debug initiative, would distribute more than 16 million mosquitoes per year over two consecutive years, all of them male, none of them capable of biting a human being. The scientific logic rests on a single biological fact: female Aedes aegypti mosquitoes, the species responsible for dengue, Zika, chikungunya and yellow fever, generally mate only once in their lifetime.

If that one mating produces no viable eggs — because the male carried an incompatible strain of wolbachia, a naturally occurring bacterium found in many insects — the female never reproduces. Release enough wolbachia-carrying males and an entire local population can be driven downward over successive generations. The males, it turns out, are also remarkably well equipped for the task: their large, bushy antennae function almost like biological radar, evolved specifically to locate females across wide areas. The approach is not untested.

More than a decade ago, researchers ran a large-scale trial on the Cassowary Coast in far north Queensland, Australia, in collaboration with what was then Google's life sciences division, now known as Verily. The results demonstrated that releasing specially bred males could dramatically suppress invasive Aedes aegypti populations in real towns under real conditions — not merely in a controlled laboratory setting. Public scepticism in the United States is understandable: questions about long-term ecological effects, what happens once the releases stop, and whether suppression can hold at the scale of two American states remain genuinely open.