ECONOTES : Cocaine Not High on Insects’ List

Botanists have long noted that coca plants, from which cocaine is extracted, have few pests.

Researchers at Massachusetts General Hospital have learned the reason: Cocaine scrambles the brains of insect predators. It does this by augmenting the action of octopamine, a neurotransmitter found mostly in invertebrate animals. In people, cocaine’s primary action is on two biochemicals similar to octopamine--norepinephrine and dopamine.

The researchers sprayed cocaine mist (of varying concentrations) on the leaves of tomato plants and then released larvae of an insect species that would normally eat the leaves.

After a few minutes of exposure, the larvae “displayed marked behavioral abnormalities, including rearing, tremors and walk-off activity,” according to a report in the Oct. 15 Proceedings of the National Academy of Sciences. At higher concentrations, the larvae stopped eating and died in a day or two.

In further experiments, the scientists showed that the drug concentration in a coca leaf is enough to boost octopamine’s activity in an insect’s brain. One action of the neurotransmitter is to suppress the appetite, which protects the plant.

The research team, led by James A. Nathanson, speculates that cocaine may have evolved as a natural insecticide.