Tiny Wasps Alter Plant Growth to Attract Mates

John Pickrell
for National Geographic News
December 2, 2002

Females of a minuscule parasitic wasp species are able to induce the plants they live in to produce a chemical perfume that attracts the males of the species, scientists report.

The discovery, detailed online in the current issue of the journal Proceedings of the National Academy of Sciences, is the first example of an animal stimulating a plant to produce a chemical sexual attractant for it.

"This is evidence of a completely different way that insects and plants can interact at the chemical level," said entomology graduate student and lead researcher John F. Tooker of the University of Illinois at Urbana-Champaign.

"No one has really considered before that insects could manipulate plants to produce a kind of sex pheromone," he said.

Plant-Animal Interactions

Pheromones are chemicals emitted by animals—including humans—that serve as a form of communication with other members of the species. Most often associated with reproduction, pheromones can also be used to signal danger, to mark trails, or to identify food sources.

Scientists have known for many years that plant-eating insects can induce chemical changes in plants. When attacked, some plants produce chemicals that poison the animals feeding on them, or signal nearby plants to ramp up their defense mechanisms.

Tobacco and corn are examples of plants that employ an alternative strategy. When attacked by herbivorous moth larvae, the plants produce volatile chemicals that attract moth predators.

"It's almost like the plants are calling for help," said Tooker's supervising professor and co-author Lawrence M. Hanks.

Tooker and Hanks are working on a project to characterize insect communities in the rapidly diminishing Midwestern prairies of the United States.

Gall Wasp Strategies

As a by-product of that study, they discovered that females of a flea-sized prairie gall wasp, Antistrophus rufus, are able to alert males to their presence by altering the smell of the plants they live in.

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