19 9 9 G R E EN CH E M I S TR Y AWA RD S C G G88 Green Chemistry August 1999 Paul Anastas, Mary Kirchchoff and Tracy Williamson of the USA EPA present the first in a series of short profiles on this year’s Green Chemistry Award winners Controlling insect pests is essential to maintaining high agricultural productivity and minimising monetary losses. Synthetic organic pesticides, from a relatively small number of chemical classes, play a leading role in pest control today.The development of new and improved pesticides is necessitated by increased pest resistance to existing products, along with stricter environmental and toxicological regulations. To meet this need, Dow AgroSciences has designed spinosad, a highly selective, environmentally-friendly insecticide.Discovery During the 1980s, Lilly Research Laboratories (Indianapolis, USA) operated a program directed at finding new natural products that possessed utility in the pharmaceutical and agrochemical industries. Soil samples from all over the world were collected, fermented, extracted, and screened in a variety of assay systems. Wherever possible, the soil samples were collected from unusual habitats, to improve the chances of finding new microorganisms.During the course of this fermentation screening program, extracts from the fermentation broth of a soil sample, collected in 1982 on a Caribbean island, were found to be active in a mosquito larvicide assay and against the southern army worm (Spodoptera eridania). The microorganism was identified as Saccharopolyspora spinosa, and it produced a family of new macrolides (molecules containing a macrocyclic lactone), now called spinosyns, of which the primary components are spinosyn A and spinosyn D.An extract of the fermentation broth that contains this naturally occurring mixture is called spinosad. Products such as Tracer® Naturalyte® Insect Control and Precise® contain spinosad as the active ingredient.Mode of action Spinosad demonstrates both rapid contact and ingestion activity in insects, which is unusual for a biological product. The mode of action of spinosad (although not fully elucidated) is characterized by excitation of the insect nervous system, leading to involuntary muscle contractions, prostration with tremors, and paralysis. These effects are consistent with the activation of nicotinic acetylcholine receptors and prolongation of acetylcholine responses through a novel mechanism.Insect spectrum Spinosad has been tested extensively on a global basis since 1990 and found to provide effective control of pests in the insect orders Lepidoptera, especially the tobacco bollworm (Heliothis virescens), the cotton bollworm (Helicoverpa zea), American bollworm (H.armigera) and armyworms (Spodoptera spp.). Environmental fate Spinosad presents a favourable environmental profile. It does not leach, bioaccumulate, volatilize, or persist in the environment. Spinosad will degrade photochemically when exposed to light after application. Because spinosad strongly adsorbs to soils, it does not leach through soil to groundwater when used properly and no buffer zones are required by the United States Environmental Protection Agency.Nontarget toxicology Spinosad is relatively low in toxicity to mammals and birds, and, although moderately toxic to fish, this toxicity represents a reduced risk to fish when compared with many synthetic insecticides in use. In addition, 70-90% of beneficial insects and predatory wasps are left unharmed by spinosad. Conclusion The unique mode of action of spinosad, coupled with a high degree of activity on targeted pests, low toxicity to non-target organisms (including many beneficial arthropods), and resistance management properties make spinosad an excellent new tool for integrated pest management.Further reading Thompson, G.; Hutchins, S. (1999) Spinosad - a new class of fermentationderived insect control agents. Pesticide Outlook 10(2), 78-81. SPINOSAD - a new natural product for insect control Spinosad is a mixture of spinosyn A and spinosyn D Visit the Green Chemistry homepage FREE electronic access to full contents of Issue 1 http://www.rsc.org/greenchem