Male orchid bees craft unique perfumes from flowers – now we know why

The perfume that male orchid bees create by collecting scents from the flowers they visit is designed to make females choose them rather than another mate.

Male orchid bees collect raw materials from multiple sources, including the orchid flowers they pollinate. These are used to concoct perfume mixtures that are stored in specialised hind-leg pouches, but the purpose of the perfume hasn’t been known for sure.

To investigate, Jonas Henske at Ruhr University Bochum in Germany and his colleagues studied an orchid bee called Euglossa dilemma, a species that has recently become naturalised in south Florida.

First, the researchers gathered perfumes from wild males. Next, they collected male bees that had freshly emerged from pupae and added the perfumes to the hind-leg pouches of some of them.

Then, Henske and his colleagues introduced the male bees, one by one, into two flight cages that already contained female bees, flowers and nesting materials. One perfumed male, one non-perfumed male and up to 20 females were present per cage at any time.

Direct observation of what happened between the bees and subsequent genetic analysis of female bees and their larvae revealed that the broods of 26 out of 27 of the females were fathered by perfumed males.

The single non-perfumed male that scored a mate turned out to have somehow acquired the perfume in his pouch. Researchers believe he stole it from another male bee, which the insects are known to do sometimes.

The composite odour created by combining different molecules allows communication of more integrated information, such as how suitable a male is to be a father, says team member Thomas Eltz, also at Ruhr University Bochum.

“This study is exciting because it very clearly demonstrates that the male orchid bee perfume has a huge effect on female mating decisions,” says Elizabeth Tibbetts at the University of Michigan.

“Over the years, lots of studies have suggested that orchid bee perfume is probably involved in female mate choice, but there are often alternative explanations,” she says. “This study experimentally alters male perfume and shows that the perfume directly influences female mate choice. It’s a very convincing experiment.”

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