The agricultural pests known as plant bugs can be a farmer’s worst enemy. These winged insects—the size of a pea or smaller—suck the sap from apples, lettuce, and other crops, causing millions of dollars in damages globally each year.
A Costa Rican flower has turned this foe into friend, however, according to a new study. One species of the so-called arum plant has evolved to attract a species of plant bug instead of a typical beetle pollinator, helping them spread their pollen far and wide. The find is the first known example of a plant harnessing plant bugs to help them reproduce.
“This is a totally new finding for ecology and evolutionary biology,” says Zong-Xin Ren, an evolutionary ecologist at the Chinese Academy of Sciences's Kunming Institute of Botany who was not involved in the work. The study “shows that flowering plants have evolved specialized relationships with pollinators outside of the usual suspects of bees, butterflies, and hummingbirds,” adds Jeff Ollerton, a Denmark-based evolutionary biologist and author of a book about pollinators.
The find comes thanks to a fortuitous all-nighter. Florian Etl, a graduate student working with evolutionary biologist Jürg Schönenberger at the University Vienna, was investigating the role of beetles in pollinating several related flowering plants in the lowland rainforests of Costa Rica. The plants look a lot like the calla lilies often sold by florists; in that the flower is a tall stalk partially surrounded by a large, modified leaf—white or purple in calla lilies, but usually green in these Costa Rican plants.
Typically, arum plants heat up at night and release an evening perfume that lures beetles to them. But on that fateful night, researchers waited all night for that to happen to one arum species in the rainforest, Syngonium hastiferum. Only in the morning did it give off an intense scent, and it wasn’t beetles that were attracted—it was plant bugs.
Intrigued, Etl performed a chemical analysis of this morning perfume. Colleagues at the University of Regensburg synthesized its major component: a previously unknown chemical they named gambanol.
When Etl coated white paper cones with the chemical, the cones attracted large numbers of the plant bugs, he and colleagues report this month in Current Biology. Moreover, when Etl covered the arum plant’s natural flowers with a fine mesh to exclude the plant bugs, no seeds were produced. “This suggests plant bugs play a key role in the pollination process," Ren says.
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Etl discovered other clues that pollination was different in Syngonium hastiferum. Unlike its relatives, the plant did not produce sterile flowers that serve as food treats for the beetles, rewarding them for their services. Its pollen was also spiny and powdery instead of the usual smooth and sticky, so it sticks but does not get stuck among the hairs of the plant bug’s body. (Beetles are smooth, so it’s advantageous for pollen to be sticky.) Finally, the plant bug pollinator is also new to science, says Etl, who has tentatively put it into the same genus, Neella, as other plant bugs known to attack these plants.
The switch from being pollinated by a beetle to a plant bug “represents a remarkable evolutionary shift," says Regis Ferriere, a theoretical ecologist at the University of Arizona. That’s because it involved changing many traits, he says: the timing and makeup of scent produced, as well as the type of pollen.
Plant bugs are the common name for a group of insects containing about 15,000 species. Given this number and the dozens of arum species, Ren expects more such relationships are just waiting to be discovered. Indeed, Etl is continuing his all-night vigils in hopes of finding them.
It’s not clear how this discovery could help farmers fight plant bugs, and indeed the plant bugs that pollinate Syngonium hastiferum consume its sap, too. But the discovery conveys an important conservation message, Ollerton says. ”Attempts to conserve pollinators need to go beyond just ‘Save the Bees’ campaigns.”
