Researchers have even discovered bacteria in solid rock many kilometres below the earth's surface, in hot springs and in salty water. These bacteria survive even though there is very little organic material available to them. Viruses are extremely tiny organisms which contain genetic information, but which cannot reproduce on their own. To reproduce, they must invade the cells of another organism and use the cells' reproductive machinery. Viruses are parasites of animals, plants and some bacteria-they must use the cells of these other organisms in order to live.
Insecticides kill or control insects, while herbicides destroy or control weeds.
Bioinsecticides and bioherbicides use fungi, bacteria and viruses to control insects and weeds. Biofungicides utilize microbes that kill fungi. Certain microbes have toxic gene products, which act only on specific plants and insects. Therefore, they have an advantage over some chemicals because they can be used in limited amounts and have much more specific effects. For example, a bacterium called Bacillus thuringiensis , B.t. for short, has been used for the past 60 years to create environmentally friendly insecticides.