page 4

Photos show how some plants can defend themselves when attacked

Photos show how some plants can defend themselves when attacked

Besides plant-to-insect and plant-to-plant interactions, chemical ecologists also study interactions among insects. Tom Baker works with pheromones, compounds emitted by individuals of a species that attract other individuals from the same species. In particular, he is examining the role of sex pheromones in insect mating disruption. “Pheromones help growers monitor orchards or fields to see when a certain pest species is present and then to time insecticide sprays accordingly,” he says. In field experiments with corn plants, Baker’s research team sets up controlled-release dispensers often to fifteen grams of sex pheromone per acre. Male moths are attracted to these dispensers, which release strong concentrations of pheromones to confuse and desensitize male moths.

Initially, the male moth is attracted to the dispenser; then it wastes time flying around the dispenser, getting used to the powerful odor. Meanwhile, nearby female moths are emitting the same pheromone, but at much lower concentrations—so the male no longer has the ability to detect the female.

“It’s sort of like walking into a kitchen where someone is cooking onions,” Baker says. “At first, you’re bowled over by the strong smell, but after a few minutes in the kitchen you don’t even notice it. You’ve become desensitized—your neurons have stopped firing and reporting the odor.” For the male moths, the fact that they can’t find the females means that mating is disrupted. They don’t mate nearly as frequently when the pheromone dispensers are present, and that disruption greatly decreases fertility.

Pheromones are useful in agriculture, Baker says, for several reasons: They are EPA approved and nontoxic, only a thimbleful per acre is needed, and they are species specific, targeting a particular pest while preserving others.

Baker is also conducting basic research into how insects sense pheromones—the process of insect olfaction. Most pheromones are simple compounds consisting of elements in very precise ratios. In research with moths, Baker and his colleagues observe how insect antennae sense pheromones, how the insect reacts, and how the insect’s brain processes the information. “We’re looking at how moths maneuver in the air and on the ground in response to plumes of pheromones,” he says. “Pheromones consist of fine odor strands, and we found that moths respond to and process each individual strand very quickly. Moth antennae are extremely sensitive and can assess the quality of a specific odor strand by strand.”

Next ...