Study Finds That Plant Emits the Scent of an Injured Honeybee to Lure Flies

Plants are liars. There, we said it. All right, fine, not all plants. But a lot of them. Meet the newest member of the botanical pants-on-fire club: a little flower that stinks like an injured bee in order to attract bee-eating flies. Researchers published a report today on the plant’s trickery in the journal Current Biology. 

Most plant deception is pretty crude. Consider the reeking corpse flower, or the bee orchid, whose lady bee-shaped flowers are irresistible to passing bee dudes. The male bees zoom in and get busy. Before too long they realize they’ve been had—but not before they’ve pollinated the devious, devious orchid.

Other plants employ slightly subtler devices. Plants in the Ceropegia family depend on flies for pollination. Their flowers are trap-shaped, so once a fly gets in, it will pretty much have to rub itself all up on the plant’s sexual parts in order to escape. But for that to happen, the fly first has to show up.

To catch a fly, you need to think like a fly. Fortunately, many of the flies that pollinate Ceropegia are fairly easy to predict. They like flying, buzzing, mating, and, most importantly, they like stealing other bugs’ food. Rather than hunting for its own honeybee, a kleptoparasitic fly waits until a predator like a spider has caught one, then buzzes down and digs in.

Flies could presumably follow spiders around until they made a kill. But it’s much more efficient to just sniff the air for the scent of a bee in trouble. It’s kind of the arthropod form of ambulance-chasing lawyers.

A team of European scientists suspected that the little South African flower Ceropegia sandersonii was using flies’ own trickery against them.

To find out, the researchers studied both the flowers and the bees. The first thing they noticed was that a spider-caught bee would eject its stinger, which released a droplet of venom. The team tested the venom and found it riddled with alarm pheromones, which, when released, would warn nearby bees to beat it.

A bee covered in kleptoparasitic flies. Check out the drop of venom at the tip of its stinger! Image Credit: Gernot Kunz

 
Next they captured and tested C. sandersonii’s oh-so-innocent floral fragrance, looking for chemical similarities with the bee venom. They found them. In an act of chemical mimicry, flowering C. sandersonii plants were in fact emitting what seemed to be appealing olfactory distress calls.

Biologist Daniel Janzen studies plant-animal relationships at the University of Pennsylvania. (He was unaffiliated with this study.) “Tropical nature is packed with these kinds of detailed eco-behavioral interactions,” he told mental_floss in an email. “It’s nice to have another one worked out.”

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