Biopesticides: Bacillus thuringiensis and Spinosad

Gardeners are looking for replacements for conventional pesticides. Some are worried about the effect of a specific chemical on their personal health.

Others are switching out of concern for the harmful impacts on the world around them. For these gardeners, biopesticides can be a gentler but effective alternative.

Biopesticides are also called natural or biological pesticides.  They are generally less toxic to nontarget organisms and the environment.

Bacillus thuringiensis and Spinosad are two common biopesticides. Specifically, they are microbial insecticides.

In general, Bacillus thuringiensis varieties are pest specific while Spinosad is more broad spectrum. 


What are Microbial Insecticides?

Microbe is a shorter name for microorganisms. These are organisms so tiny that we cannot see them with naked eye.

In the case of microbial insecticides, we’re talking about microbes that are harmless to people, but deadly to insect pests.

The active ingredient in a microbial insecticide is the microbe itself. It may be bacteria, fungi, protozoa, microbe-carrying nematodes, or even a virus.

 Bacillus thuringiensis (Bt) is naturally present in the soil, water, and on plant surfaces. Saccharopolyspora spinosa (Spinosad) lives in the soil as well.

How to Microbial Insecticides Work?

Like humans and their garden plants, insect pests are vulnerable to microbes. Microbial insecticides take advantage of this weakness.

They contain a high concentration of a microorganism found in nature and known to affect different insect pests. The microbe preys upon the pest.

As a result, the pest becomes too sick to continue eating or unable to reproduce.

Bt affects the larval (caterpillar) stage of multiple pest groups. When caterpillars, like hornworms, eat Bt, it begins to ferment in their intestine.

The toxins it produces cause the caterpillars stop eating and die a few days later.

Specific varieties of Bt target specific pest groups. Bt var. kurstaki targets caterpillars (butterfly and moth larvae), for example.

Bt var. israelensis targets fly larvae, including mosquitoes. Be sure to choose the correct variety of Bt for your insect pest. 

Spinosad is a more broad-spectrum microbial insecticide. It affects caterpillars, leaf miners, flies, thrips, beetles, and spider mites.

Spinosad works by attacking the nervous system once the pests eat it. Like Bt, the pests stop eating and die a few days after.


Post time: Mar-10-2023

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