Bacillus thuringiensis

An insecticide exists, which is based on the spores and toxins produced by a bacterium: Bacillus thuringiensis (Bt). It is a very specific product, which can be used to control caterpillars (larvae of moths and butterflies).

Bt is not a contact poison, but acts like a stomach poison. It must be eaten by the insects to be active. It will only kill caterpillars which feed on plant parts that were sprayed with the product. As such, it will be more effective against caterpillars that feed externally on leaves. It is less effective against internal feeders such as stem borers or leaf miners.

Bt is a biological agent rather than a synthetic chemical. Compared to most chemical pesticides, Bt has the advantage that it does not kill the beneficial insects or spiders. It is also less toxic and thus safer for the user (farmer) and for the consumers.

Plutella adultAn important cabbage pest is the diamond-back moth (Plutella xylostella). If all other methods have failed to keep this pest under control, Bt could be applied rather than synthetic pesticides. Adult of the Diamond-back moth.

Bt is effective against caterpillars, but it works rather slowly. The insects don’t drop dead immediately. After ingesting Bt the caterpillars will first slow down and stop feeding. They die after a few days.

Farmer with Bt
Farmer shows a bottle Bt

Read more about Bt on these pages:

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