Spinosad

Spinosad
Name	Spinosad
IUPAC name	Mixture of (2R,3aS,5aR,5bS,9S,13S,14R,16aS,16bR)-2-[(6-deoxy-2,3,4-tri-O-methyl-α-L-mannopyranosyl)oxy]-13-(2R,5S,6R)-5-(dimethylamino)tetrahydro-6-methyl-2H-pyran-2-yl]oxy]-9-ethyl-2,3,3a,5a,5b,6,7,9,10,11,12,13,14,15,16a,16b-hexadecahydro-14-methyl-1H-as-indaceno[3,2-d]oxacyclododecene-7,15-dione and (2S,3aR,5aS,5bS,9S,13S,14R,16aS,16bS)-2-[(6-deoxy-2,3,4-tri-O-methyl-α-L-mannopyranosyl)oxy]-13-OtherNames = Spinosad A and D mixture | Section1 = | Section2 =

Spinosad. It is a naturally derived insecticide produced by fermentation of the soil actinomycete *Saccharopolyspora spinosa*. This compound is a mixture of two macrocyclic lactones, spinosyn A and spinosyn D, and is renowned for its efficacy against a broad spectrum of insect pests with minimal impact on many beneficial organisms. Its unique mode of action and favorable environmental profile have led to its widespread adoption in integrated pest management programs globally.

Chemical properties and structure

Spinosad is characterized as a mixture of two structurally similar molecules known as spinosyn A and spinosyn D. These compounds are tetracyclic macrolides with a unique 12-membered macrocyclic lactone core fused to a benzopyran moiety. The structures feature a rhamnose sugar attached via a glycosidic bond and a forosamine amino sugar, which are critical for biological activity. The primary difference between the two components is an additional methyl group on the benzopyran ring of spinosyn D. The substance typically appears as a white to off-white crystalline solid with low water solubility but high solubility in many organic solvents like acetone, methanol, and dichloromethane.

Mechanism of action

The insecticidal activity of spinosad stems from its action on the nicotinic acetylcholine receptors and gamma-aminobutyric acid (GABA) receptors in the insect central nervous system. It persistently activates the nicotinic acetylcholine receptors, leading to involuntary muscle contractions and tremors. Concurrently, it disrupts function at GABA receptor sites, which normally mediate inhibitory neurotransmission. This dual action causes rapid excitation of the nervous system, resulting in paralysis and death of target insects. This unique receptor profile contributes to its low cross-resistance with other insecticide classes such as organophosphates, carbamates, and pyrethroids.

Agricultural and horticultural uses

Spinosad is registered for use on a wide variety of crops by agencies like the United States Environmental Protection Agency and the European Food Safety Authority. It is highly effective against key pests including thrips, leafminers, caterpillars (e.g., diamondback moth, tomato pinworm), fruit flies, and certain beetle species. Common applications include its use in fruit orchards, vegetable farms, and ornamental plant production. It is formulated as suspensions, granules, and baits, and is a cornerstone in organic farming systems, being approved by organizations like the Organic Materials Review Institute.

Veterinary and medical applications

Beyond agriculture, spinosad has significant applications in veterinary medicine. It is the active ingredient in prescription products like Comfortis for controlling flea infestations in dogs and cats. Its mode of action provides rapid kill of adult fleas. In human medicine, a topical suspension formulation has been developed and approved by the U.S. Food and Drug Administration for the treatment of head lice infestations, offering an alternative to traditional pyrethrin-based pediculicides. Its use in these fields is valued for its efficacy and favorable safety margin.

Environmental impact and safety

Spinosad exhibits low toxicity to mammals and birds but is highly toxic to aquatic invertebrates and bees if exposed directly. However, its rapid photodegradation on foliage and strong adsorption to soil particles reduce its environmental persistence and potential for runoff. It is considered compatible with integrated pest management due to its selectivity, sparing many predatory insects, parasitoid wasps, and lady beetles. Regulatory bodies classify it as a reduced-risk pesticide, though guidelines from the Environmental Protection Agency mandate precautions to protect pollinators and aquatic ecosystems.

History and development

Spinosad was discovered in 1982 during a soil screening program by scientists at the Dow AgroSciences research facility. The producing organism, *Saccharopolyspora spinosa*, was isolated from soil samples collected from an abandoned rum distillery in the Caribbean. After extensive research and development, the first commercial product received registration from the United States Environmental Protection Agency in 1997. The discovery team, including researchers like Gary D. Thompson, was later honored with the Presidential Green Chemistry Challenge Award in 1999 for developing this environmentally benign technology.

Category:Insecticides Category:Macrolides Category:Green chemistry