WASHINGTON (Reuters) - Orchids that mimic female wasps may not only waste the time of the male wasps they lure into spreading their pollen -- they also seduce them into wasting valuable sperm, Australian researchers reported on Wednesday.

And the flowers benefit twice -- getting help in their own reproduction, and perhaps indirectly producing more male pollinators in the process.

Some of the most exotic orchids are known to have evolved their convoluted shapes to attract insects, who unwittingly collect and transfer pollen as they try to mate with the flowers.

"The effect of deception on pollinators has been considered negligible, but we show that pollinators may suffer considerable costs," Anne Gaskett of Macquarie University in Sydney and colleagues reported.

"Insects pollinating Australian tongue orchids (Cryptostylis species) frequently ejaculate and waste copious sperm," they wrote in a report in The American Naturalist.

It is not harmless to the wasps, who may suffer more than an inconvenience. "Male pollinators can prefer orchids to real females, prematurely end a copulation with a real female to visit an orchid, or be unable to find real female mates among false orchid signals," the researchers wrote.

"Unquestionably, producing sperm, ejaculate, or seminal fluids is costly for many animals. The energetic demands of sperm production can result in reduced body mass, a shortened life span, or limited lifetime sperm production," they added.

But this arms race of sexual trickery works in more than one way for the flower. "We also show that orchid species provoking such extreme pollinator behavior have the highest pollination success," they added.

"How can deception persist, given the costs to pollinators?"

They found that the wasps who frequent these flowers are haplodiploid species. Like bees, ants and similar species, offspring produced by sexual unions are female, while females can also produce males asexually.

"Therefore, female insects deprived of matings by orchid deception could still produce male offspring, which may even enhance orchid pollination," the researchers wrote.

Gaskett's team examined flowers after wasps visited them and found the hoodwinked males did eventually learn their lesson.

"With experience, male Lissopimpla excelsa wasps become less likely to copulate with and pollinate sexually deceptive Cryptostylis orchids," they wrote.

(Reporting by Maggie Fox; Editing by Eric Beech)