A rare South African plant produces a fluid and scent that mimic honeybee blood to entice scavenging jackal flies to pollinate its flowers.
Jackal flies from the genus Desmometopa聽ordinarily feed on the blood of insects, especially honeybees, that have been killed by spiders and praying mantises. They are alerted to the presence of a free meal by the smell of spilt bee blood, or haemolymph.
at the University of KwaZulu-Natal in South Africa wanted to know why the inconspicuous, green, star-shaped flowers of Ceropegia gerrardii attracted four species of jackal fly in the absence of any injured honeybees.
Advertisement
Years earlier, she had discovered that Ceropegia sandersonii, a closely related plant, traps jackal flies inside its flowers and then releases them. That plant attracts the flies by mimicking the scent of stressed or injured bees.
鈥淪eeing these flies on the flowers of C. gerrardii implied they would have the same mimicry strategy as that trap flower,鈥� says Heiduk.
She noticed that C. gerrardii flowers produce tiny droplets on their petals and suspected that it was a kind of fake insect blood to entice flies to land on the flowers and spread their pollen.
To investigate further, she and her team collected scent samples from the flowers and analysed their chemical make-up with a mass spectrometer. They then attached micro-electrodes to the flies鈥� antennae and measured their responses to various scent molecules from the flowers. 鈥淚f the antennae responded, that allowed us to say, 鈥極kay, the fly can perceive that particular compound鈥�,鈥� she says.
Next, they placed small glass vials of solvent containing combinations of scent compounds on stakes in the ground within the plants鈥� grassy habitat. With these they could determine which mixture attracted the flies, and they caught visiting flies to confirm they were the same species as those that visited the flowers.
The researchers also analysed the droplets of liquid on the flower petals and found they contained a protein and sugar mixture similar to haemolymph, though it is unclear if the flies are disadvantaged by feeding on this fake blood rather than the real thing.
The benefit of this subterfuge to the plants, however, was clear: if the researchers kept flies from landing on wild-growing C. gerrardii flowers by placing bags over them, the plants didn鈥檛 produce any fruit.
C. gerrardii is endangered, with only 2500 mature plants estimated to grow in tiny patches within grasslands threatened by invasive plants, fires and overgrazing.
鈥淭here鈥檚 a lot to worry about in terms of long-term survival and protection of these species,鈥� says Heiduk.
New Phytologist
