‘Bisexual’ beetles don’t swing both ways ... they’re just inept

IT IS a finding likely to send shock waves through the admittedly niche-interest world of insect sexual politics.

Scientists have concluded that male insects that mate with other males are not gay, or even bisexual. They are just hugely incompetent.

More than 100 species of insects engage in some kind of same-sex mating. In some it is more common than heterosexual mating.

The practice has long puzzled researchers because it takes time and energy, risks disease and injury and offers no genetic benefits. It was speculated that it may show social dominance, a practice behaviour, or simply a sexual preference.

But now scientists at the School of Biological Sciences at the University of East Anglia (UEA) have concluded that beetles are simply inept.

In the study, published in the journal Animal Behaviour, results showed that within populations of mostly female beetles, the males were much more likely to copulate with other males. Researchers concluded that, where there was much less pressure to find the right mate, the beetles simply made more mistakes.

By contrast, when the population was male heavy, and there was an intense pressure on males to find the right mate and same-sex matings were less frequent.

“In the male-biased lines we found the male beetles were much more competitive at finding females and mating them efficiently,” said Kris Sales, the lead researcher. “In the female-biased lines, it’s highly likely that a male mating randomly will mate with a female and produce offspring. In these lines it looks as though males have lost their abilities to discriminate between male and female mates.”

The team kept populations of red flour beetles at differing sex ratios of 90 per cent male or female. To check mating motivation, a male beetle from each populations was given the choice of mating with either a female or a male, and their behaviour was monitored.

Although the amount of sexual activity was similar in both groups, the researchers found that, in the population that was predominantly male, the male beetles were much more selective in their choice of mate.

They were more likely to mount the female first and spend a longer amount of time with her. In the population that had more females, the males were just as likely to mount a male as a female one and seemed to randomly choose the partner.

While the research shed light on an interesting insect world paradox, researchers said the work did not reveal much about same sex behaviour in humans and other more complex animals.