JOY OF SEX TURNS MALE WASPS COLOURBLIND

Australia's plant world is a hotbed of sexual intrigue with a seductive native orchid trying to outwit a randy male wasp, new research shows. Anne Gaskett, a PhD student from Macquarie University in Sydney, has uncovered what she says is the first evidence of an escalating evolutionary arms race between orchids and their insect pollinators.Her study uses advanced colour technology for the first time to understand how five species of native tongue orchids trick a male wasp into believing he has found a sexual partner.She says the findings will help to develop environmentally sensitive pest controls and conserve orchid species. Gaskett looked at the orchid dupe wasp (Lissopimpla excelsa). And she says as far as the male is concerned, tongue orchids have "curves in all the right places". But the wasp is fooled for only so long.Her research found that even after just a few exposures to the orchid the wasp avoids trying to have sex with it. Gaskett, from the Department of Biological Sciences, says the orchid must then enhance its mimicry of the female wasp to continue to attract the male wasp and pollinate. "This means only the most persuasive orchids will continue to reproduce," she says.

Persuasive
Orchids are the only plant whose flowers trick insects using such sexual deception. The aim is to convince the insect to 'mate' with them. The insect accidentally collects pollen on its body, which is then transported to another flower. Gaskett says the orchid dupe wasp is attracted to and pollinates five species of tongue orchid (in the genus Cryptostylis). This is unusual as normally one insect pollinates one species of orchid. She says this means the five orchid species, which look completely different to the human eye, must look and feel the same to the male wasp. "I wanted to know what it was about the five orchids that could persuade the male that they were all a female [wasp]," she says. Gaskett used a spectrometer to analyse the colours of four of the five species and a female wasp. Taking into account factors including the background colour, ambient light and colour range of the male wasp's receptors, she found the orchid replicates almost exactly the colours of the female orchid dupe wasp. She has also found 'hidden shapes' that feel like a female wasp to the male, including 'love handles' the male wasp grip onto while mating.

Deceptive seduction
Cryptostylis orchids were the first genus of Australian orchids found to show this type of deception. The finding, in the 1920s by schoolteacher-turned-naturalist Edith Coleman, was published in the Victorian Naturalist and received worldwide attention. Gaskett says the sexual warfare between the wasp and orchid occurs in some of Australia's most public places as the tongue orchid is common in urban and regional Australia and New Zealand. "People walking past don't realise there is a hotbed of sexual intrigue going on right beside them in the park," Gaskett says. She is now studying the perfume of the orchids and testing them on wasp antennae to look at the role of smell in the seduction process.