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Bacillus thuringiensis (B.t.)

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What is B.t. ?

B.t. is the abbreviation for a species of bacteria, Bacillus thuringiensis, commonly found in nature. These bacteria can live and multiply within the bodies of insects, and produce spores and protein crystal toxins which can result in death of the insect host. In order to work as a biological insecticide, B.t. or its spores or crystal toxins must be must be eaten by the insect. Inside the insect, the crystal toxins bind to cells of the gut wall, and cause these cells to break apart. Within minutes of eating B.t, the insect stops feeding. Death will occur, primarily by starvation, in about 2 to 5 days.

Why use B.t.?

B.t. is considered non-toxic to plants and to animals other than certain insects. It is highly selective, and only kills certain insects. It does not kill most beneficial insects such as lady beetles and parasitic wasps. B.t. is also non-polluting and can be safely used where other pesticides may cause contamination to surface and groundwater. B.t. is cost effective when compared with other pesticides.

What pests does B.t. control?

B.t. is effective against the larvae, or immature stages, of insects but not the adult stages. There are many strains of B.t., and each is most effective against certain insect pests. Some of the strains include:

  • B.t. var 'aizawa' - for control of larvae of wax moths and other moth species
  • B.t. var 'israelensis' - larvae of mosquitoes, black flies, and other flies
  • B.t. var 'kurstaki' - many types of caterpillars
  • B.t. var 'San Diego' - larvae of elm leaf beetle
  • B.t. var 'tenebrionis' - larvae of elm leaf beetle

How should B.t. be applied?

  1. Choose the right product, i.e. the proper strain, of B.t. for the insect to be controlled.
  2. Avoid high pH water when mixing B.t. sprays since high pH can reduce effectiveness.
  3. Use B.t. spray within 12 hours of mixing.
  4. Time applications to coincide with most vulnerable life stage of pest.
  5. Add a spreader/sticker to the tank mix to improve the effectiveness of the spray. Reapply the spray if heavy rainfall occurs within 8 hours of application.

Written by: Ron Kujawski
Revised: 10/2011

Commercial Horticulture
Commercial Horticulture topics: 
Insects and Mites