Some microbes can be fermented to produce an insecticide such as abermectins, a fermented product of Streptomyces avermitilis (Dybas 1989) used in baits for household insect pests. The best known home gardening product of this type is spinosad. Metabolites of Saccharopolyspora spinosa, a soil-inhabiting bacteria that is fermented, are the basis for this new class of insecticide. The fermentation process has been industrialized to produce commercial insecticides.
Spinosad. Spinosad is composed of spinosyns A and D. The fermented product is very toxic to caterpillar pests such as cabbageworm, cabbage looper, diamondback moth, armyworm, and cutworm, as well as fruit flies such as spotted wing drosophila. Spinosad can act on a susceptible insect’s stomach and nervous system.
It is primarily ingested by feeding insects but can have some efficacy when sprayed directly on insects. Affected pests cease feeding and undergo partial paralysis within minutes upon exposure to spinosad, but it may take up to two days for the insects to die (Salgado et al. 1998).
Spinosad is systemic in some plants. Depending on the fermentation process and formulation, some spinosad insecticides are considered organic. Spinosad has low toxicity to many beneficial insects that prey on pests, and is nontoxic to mammals and other vertebrates, with the exception of some fish (e.g., slightly toxic to trout). Spinosad is toxic to bees for three hours after application, so do not apply to blooming plants during the day.
Because it is selectively toxic for many pest species and relatively safe to nontarget species, spinosad has become highly desirable as an organic insecticide. However, its popularity raises concerns about the development of pest resistance. Therefore, alternate the use of spinosad with other products.