Many of the pests that plague gardeners are caterpillars and other leaf-eating insects. Only caterpillars can be controlled with the well-known biological pesticide Bt (Bacillus thuringiensis), but a newer biological pesticide, spinosad, can control caterpillars as well as leaf miners, thrips, Colorado potato beetle larvae, and even fire ants and fleas.
The spinosad parent bacterium, Saccharopolyspora spinosa, was discovered in 1982 in an old Caribbean rum still. It was soon found that these bacteria produce a substance that works as a neurotoxin in many (but not all) insects. Susceptible insect species that are exposed to spinosad become excited to the point of exhaustion, stop eating immediately and die within two days.
Similar to Bt, spinosad breaks down in sunlight, so late-day applications will better expose insects to the toxins. Spinosad has a longer period of residual effectiveness compared with Bt, often providing good protection from pests for five to seven days. Generally, spinosad is most effective against insect larvae, so it’s important to look carefully for eggs and feeding insects before you spray.
The Organic Materials Review Institute currently lists 21 approved spinosad products, including the following for use in the garden: Entrust Naturalyte Insect Control, Green Light Lawn and Garden Spray with Spinosad, Monterey Garden Insect Spray, and others. Several more have been approved for control of fire ants.
Uses for spinosad go beyond the garden — it’s even being used to prevent fleas in dogs. Given monthly in the form of a pill, a product called Comfortis makes dogs uninhabitable to fleas for 30 days. Spinosad is also the active ingredient in a product called Natroba, recently approved by the FDA to control head lice, which affect 6 to 12 million American children every year. Spinosad provides a reliable alternative to lice-control products containing permethrin (a synthetic pesticide used as the active ingredient in several treatments), and is especially helpful in cases involving permethrin-resistant lice.
A note of caution: Although spinosad is not as broad-spectrum nor as long-lasting as many synthetic insecticides, it can kill bees and other beneficial insects along with pests. So use it sparingly — only when you think you have to.
(To help distinguish good bugs from pests, we recommend the book Garden Insects of North America. — MOTHER)
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