From the late 1800's to the 1940's BI's were used extensively in the US until synthetic organic insecticides were introduced. From 1945 to the 1970's the only BI used widely was pyrethrin. During the last 15 years interest in BI's has increased as a result of environmental concerns and because of insect populations that are resistant to conventional chemicals. BI's can be preparations of the crude plant material, extracts or resins. The crude plant material is usually ground into a powder and marketed full strength or diluted with a carrier.
Carriers can be talcs, clays, diatomaceous earth, emulsifiable concentrates and suspensions.
Rotenone, pyrethrum flowers, sabadilla seeds, ryania stems and neem seeds are often ground into powdered form. Plant extracts or resins are removed and concentrated through refinement. Examples of extracts include nicotine, limonene and linalool. Some materials can be used shortly before harvest. Botanicals act quickly to stop feeding although they may not cause death for days.