College of LAS « Illinois

Entomology

Tiny Wasps Enlist Plants to Woo Mates

Wasp alters mix of chemicals the plant produces.

Many insects waft sex pheromones through the air to lure a mate. But LAS researchers recently discovered the first insects that trick plants to do their wooing for them. A tiny parasitic wasp that lives inside common prairie plants attracts mates by inducing the plants to alter the mix of chemicals it produces.

The flea-sized gall wasp that lives most of the year as larvae inside the stems of compass plants before metamorphosing into adult wasps, which escape each spring to see the world, mate, and die. As he walked in a prairie one day, former entomology graduate student John Tooker spotted adult male gall wasps staking out territory along the stem of compass plants. Each would charge and head-butt other males that invaded his turf. Tooker kept watching, and eventually an adult female would chew her way out of the stem exactly where the male was guarding.
" Tooker wondered how they knew where the female would emerge," says entomology professor Lawrence Hanks, Tooker's advisor.

It turned out that the male wasps smell their way to a mate. Female wasps inside the stem manipulate nearby plant cells to alter the mix of chemicals called pinenes that they produce. Male wasps then smell the altered pinene mix from outside the stem.
The results could lead to a new method of biological pest control, Hanks says. If other plant-eating insects change the mix of plant chemicals, predatory insect-eating creatures like beetles that eat them might smell it, too. If so, then spraying the right chemicals might attract the beetles to munch away on plant-eating bugs, which would protect crops.

October 2003