Many plants contain chemicals that are toxic to insects. Some of these have been known about for a long time and a few have been commercially developed and processed into an insecticide product used for pest control. Because these naturally occurring insecticides are derived from plants, they are called botanical insecticides or botanicals.
The best known, and most widely used botanical insecticide is pyrethrum, a mixture of different insecticidal compounds found in the dried flower head of the pyrethrum daisy, Chrysanthemum cinerariaefolium. Other botanicals include rotenone, extracted from the roots of Derris and Lochocarpus plants, sabadilla, derived from ripe seeds of a tropical lily called Schoenocaulon officinale, ryania which comes from the woody stems of the Ryania speciosa shrub, the formerly-popular insecticide nicotine extracted from tobacco and limonene and linalool, compounds refined from citrus oils extracted from orange and other citrus fruit peels. The newest commercial botanical is Neem, an insecticide also known by the active ingredient name azadirachtin, derived from the neem tree, Azadirachtin indica.
The wide sources of these botanical insecticides should cause us to not be surprised when other chemical compounds in plants turn out to be insecticidal. For example, caffeine has been shown to be an insect repellent at low concentrations and lethal when fed to some insects at high concentrations. Other insects survived high concentrations of caffeine but failed to reproduce.
Now comes word that cocaine also acts as a natural insecticide. The following article is adapted from Ag Chem Notes, Penn State University, December, 1993, by way of Pesticides Coordinator Report, University of the District of Columbia, January, 1994.
Cocaine has been found to have surprising insecticidal effect at levels in which it occurs naturally in plants. Cocaine is obtained from the leaves of coca plants, but its natural function in plants has been previously unknown. Curious about another group's earlier observation that coca plants tend to be relatively pest free, James A. Nathanson and coworkers in the department of neurology at Massachusetts General Hospital in Boston decided to examine cocaines effects on feeding in insects (Proc. Natl. Acad. Sci. USA, 90:9645, 1993). Their experiments showed that insect larvae exposed to cocaine-sprayed leaves displayed marked behavioral abnormalities, including rearing, tremors and walk-off activities. Their data indicate that cocaine's toxicity stems from its ability to block reuptake of octopamine, a key insect neurotransmitter and hormone that regulates movement, behavior and metabolism. The researchers point out that cocaines effects in humans are also caused by blockage of reuptake of a neurotransmitter, dopamine. Cocaine's effects in humans are likely an unintended evolutionary side effect of its ability to block amine uptake in insects.