THREE little words – not tonight, dear – tends to be enough to cool the ardour of even the most red-blooded chap.

Now a colony of previously frisky female stick insects has been found to have not only turned off sex altogether but wiped out their male suitors in the process.

In the ultimate case of sisters doing it for themselves, the females from a species of stick insects brought to the UK from New Zealand have stopped reproducing in the traditional manner and evolved into a female-led population.

It’s meant the demise of the colony’s male Clitarchus hookeri stick insects, and sparked a warning from researchers that, in theory at least, the same could be replicated in humans. While it’s unlikely that the world’s men will come to the same sticky end, the female insects’ shift away from having sex to becoming asexual has intrigued researchers who are now trying to figure out how it’s happened so rapidly.

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The stick insects originally hitched a lift from New Zealand’s north island to the UK on plants being brought to the subtropical Tresco Abbey Garden more than 70 years ago. They set up colonies on various sites on the Isle of Scilly off the coast of Cornwall.

While it was widely known that the species can be both sexual and asexual – with the females producing ready-made fertilised eggs – biologists from Massey University in New Zealand found the colony had originated from a sexual group, but they had apparently evolved to no longer requiring to have sex in order to reproduce. As a result, the local population of Scilly Isles stick insects is now entirely female, yet still reproducing.

Dr Mary Morgan-Richards, from New Zealand’s Massey University, told the BBC: “We were able to identify a population that had moved from New Zealand to the UK, left behind males, and in just 100 generations had evolved barriers to sexual reproduction. “Just one or two eggs could’ve resulted in the whole population that’s surviving there now.”

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The scientists traced the colony’s origins to a specific location and found that despite living in a similar habitat with similar food, their Kiwi cousins continued having sex and reproducing equal numbers of male and females. And, even when reintroduced to their New Zealand counterparts, the UK stick insects retained their “no sex, we’re British” patterns of behaviour. “In just 100 generations the females had not just become asexual but they actually had a barrier to fertilisation.

So even when we brought them back to New Zealand and gave them males to mate with, they still didn’t use the sperm. “We think very rapid switches in reproductive strategy within a single species will help us to understand the advantages to sexual reproduction and why it’s so prevalent,” she added.

The research is said to have presented scientists with several routes for further study, among them whether sex was even a useful process for the species at all when it was clear that the females were perfectly efficient at reproducing alone.

But while that would appear to sound the death knell for the male of the species, the news was not entirely bleak. For the team also found evidence of New Zealand populations reverting from being asexual to using sexual reproduction.

Dr Morgan-Richards added: “There are quite a few species that are asexual, we see species of stick insects in northern America and Europe where they are completely asexual. “Stick insects tend to be very flexible. Asexuality is rare in multiple cellular organisms, we don’t understand why that could be. But there are still lots of examples in nature where you find exceptions to that rule.”

She added: “There is huge diversity out there so all sorts of things are possible, there are examples of asexuality in mammals. Anything is possible so humans could become asexual. It’s much more likely that people will clone themselves and mutations could happen that way. It’s not very likely though.”