Stay Away From Tobacco

Natural History, Oct, 2001 by Heather Van Doren

Scientists have tong known that plants can send a strong message to hungry insects by releasing volatile, Sniffable chemicals. Now a team of entomologists led by Consuelo De Moraes, of the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, Florida, has found that not only does at least one plant--Nicotiana tabacum, the most common species of tobacco--emit volatile chemicals by day, it emits a different blend of chemicals by night. And this cyclical chemical production is closely linked to the life cycle of the plant's main nonhuman consumer, the tobacco budworm (Heliothis virescens), whose adult stage is a nocturnal moth.

The newly discovered nighttime blend of volatile compounds released by N. tabacum can be detected by receptors on the moth's antennae; the female moth interprets the compounds as a warning that the plant is saturated with competitive insect larvae or that it is of low nutritional value. Either way, she tends to get the message and go elsewhere to lay her eggs.

If, however, a moth manages to lay eggs on N. tabacum's leaves, and caterpillars emerging from those eggs feast on the leaves in the Light of day, the caterpillars' saliva is drawn into the plant's vasculature. There it stimulates the production of daytime-only compounds. These attract the tobacco budworm's natural predators, which follow the wafting chemicals to the infected plant and dine on the caterpillars. The researchers are now exploring whether the moths are "making sophisticated choices based on the likely presence of particular Larval competitors and perhaps even of particular predators and parasitoids." ("Caterpillar-Induced Nocturnal Plant Volatiles Repel Con-specific Females" and "Night Moves of Pregnant Moths," Nature 410, 2001)