Although it's associated with nasty cigarettes, the tobacco plant is also a potential source of vaccines, biofuel and antibiotics. Now, a chemical from the plant is also being used as a bug repellent for crops, which could replace eco-unfriendly insecticides.

One of the problems with insecticides is the fact that they not only kill crop-eating insects, but also beneficial species such as bees and butterflies. Additionally, through storm runoff and soil leaching, they make their way into rivers and lakes, causing widespread environmental damage.

The tobacco plant, however, is able to protect itself from insects on its own. It does so by producing a chemical known as cembratrienol (or CBTol for short) in its leaves. Bugs are repelled by the odor of CBTol, and as a result tend to stay away.

Led by Prof. Thomas Brück, a team from the Technical University of Munich isolated the sections of the tobacco plant genome responsible for the formation of CBTol molecules, and then incorporated those into the genome of genetically-modified E. coli bacteria. When fed with wheat bran (obtained as a byproduct from grain mills), those bacteria subsequently produced CBTol.

Using that chemical, the scientists created a biodegradable, non-toxic and environmentally-friendly repellent that can be sprayed directly onto crops of all types. In lab tests, aphids passed over plants that were treated with the spray, going instead for untreated plants. And as a side benefit, the repellent also kills several types of gram-positive bacteria that are harmful to humans.

"With our approach, we are opening the door to a fundamental change in crop protection," says Brück. "Instead of spraying poison, which inevitably also endangers useful species, we deliberately merely aggravate the pests."

A paper on the research was recently published in the journal Green Chemistry.