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Love Stinks: The Bees and the Beetles

4 May 2000 7:00 pm
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Beetle larvae try to look like female bees.

"She was a looker, but she was no lady!" Such might be the lament of deceived male bees in the Mojave Desert, where entomologists have found that larvae of a parasitic beetle gather in clumps redolent of frolicsome female bees. The larvae with this come-hither look are the only parasites known to gang up to seduce their host.

People trying to lure a mate aren't the only creatures who'll pretend to be something they're not. A species of South American orchid grows a bee-shaped blossom that attracts amorous male bees, which get covered with pollen when they try to mate. And plenty of animals cooperate in some fashion, from chimps hunting together to ants erecting elaborate colonies. But only the parasitic beetle Meloe franciscanus turns both tricks at the same time. Fittingly, it's a relative of the putative aphrodisiac, the Spanish Fly.

Entomologists John Hafernik and Leslie Saul-Gershenz of San Francisco State University knew that the millimeter-long beetle larvae ride around on a species of bee called Hapropoda pallida. Eventually, the larvae make their way into the nests of these solitary bees and eat their eggs. They also knew that the larvae collect in curious clumps on bushes and blades of grass. Observing dozens of these, the researchers found that male bees often seek and land on the clumps, only to struggle away burdened with the entire mass of several hundred larvae. Female bees show little interest in the clumps, and male bees ignore scentless decoys that only look like piles of larvae. The researchers hypothesize that the larvae give off a fake sex scent that attracts the male and that the clumps look enough like female bees to dupe the excited males into making their move. Once infested, the males may pass the larvae to the real females they mate with, who carry them into their nests.

The observations, reported in the 4 May issue of Nature, provide solid evidence that the larvae attract the bees, says Meloe expert John Pinto of the University of California, Riverside, although he's not yet convinced that the larvae mimic the scent of female bees.

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