Bacteria that specialise in killing only the male of the species have led to the creation of the demanding female that never has a headache.

Male butterflies and ladybirds that survive the so-called Herod Bug are in such demand that exhaustion is the only bar to sexual satisfaction.

When free of the Wolbachia bacterium the butterflies are lucky to persuade one female to mate with them, but when the Herod Bug is present they — purely out of a sense of duty, of course — have to satisfy up to 50 partners.

Biologists studying the Hypolimnas bolina butterfly in the Pacific have found that its patterns of sexual behaviour are turned upside down by the Wolbachia family of bacteria.

Males start turning down opportunities to procreate because they are too tired to go on while females become promiscuous sexual predators.

“Female promiscuity actually rises when male numbers are reduced,” said Dr Sylvain Charlat who led the University College London study published in the journal Current Biology.

“Greater numbers of female partners leads to fatigue in males. They start producing smaller sperm packages. Unfortunately, the female butterflies instinctively know. This just makes them more rampant.”

The effects are much the same in Britain’s ladybirds, though less pronounced because the insects are naturally promiscuous.

Ladybirds will spend hours mating under normal conditions but when the Wolbachia bacterium is around the male is thought to bring proceedings to an end much quicker.

Greg Hurst, one of the senior researchers, said one of the key findings of the butterfly study was that while a huge proportion of the males could be wiped out by the bacteria the overall population of the colony remained viable.

“It’s amazing that the numbers of male butterflies can get so low and yet the population is sustainable and stable,” he said.

“You don’t need many male butterflies to continue the population. This is partly because the decision to mate is mainly under female control.” “ B u t the males have to work harder. We think the males must be able to get through 50 females - though they put less effort into each mating.”

Scientists involved in the study analysed the impact of the Wolbachia bacteria on populations of butterflies on islands in the Pacific and South East Asia.

Wolbachia affects huge numbers of insects with 80 per cent of all species estimated to be attacked by the parasitic bacteria.

Previous studies have suggested that understanding the role of Wolbachia in insects may lead to the possibility that malaria-carrying mosquitoes can be controlled effectively.

Dr Charlat added: “Male-killing bacteria are found in many insect species including the British ladybird. We wanted to know what the effect of the bacteria is on the mating system, and here we’ve shown that butterfly mating patterns are strongly determined by the killer bacteria.”

The report concluded: “Contrary to expectation, increasing female bias in the population leads to an increase in female mating frequency as a response to the decreasing size of spermatophores.

“The decrease in male investment per mating in female- biased populations is not due to the evolution of different ejaculate delivery strategies but rather to the depletion of male reproductive reserves.”

The Herod Bug

— The Wolbachia bacteria attacks insects, mites, spiders and nemotodes

— It can kills males, turn them into females or make females sterile

— Wolbachia was first identified in the 1920s in a species of mosquito

— The microbe has been linked to elephantitis and river blindness in humans

Source: Times database

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