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Title: Screening Bacillus thuringiensis strains for toxicity against Manduca sexta and Plutella xylostella

item Martin, Phyllis
item Blackburn, Michael - Mike

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2007
Publication Date: 5/17/2007
Citation: Martin, P.A., Blackburn, M.B. 2007. Screening Bacillus thuringiensis strains for toxicity against Manduca sexta and Plutella xylostella. Biological Control. 42(2):226-232.

Interpretive Summary: Using bacteria specifically pathogenic to insects to control pests is a good alternative to chemical control. However, it is a time-consuming and expensive process to find the appropriate bacteria to use. We developed an easier and more effective way to identify bacteria that can kill pest insects, from over 10,000 potential candidates, by testing bacteria in groups for toxicity. If the combination of bacteria that was fed to insects was toxic, then the different bacteria were tested separately to find the toxic bacteria in the group. Any group that was not toxic was eliminated from further testing. This process, combinatorics, reduced the number of tests required to find bacteria that are toxic to insects by 60%. Twenty-eight toxic bacteria out of a total of 147 were found by this process. The procedure would be useful to scientists who are trying to identify and use bacteria to control insects.

Technical Abstract: Screening Bacillus thuringiensis (Bt) isolates or strains for toxicity has traditionally been performed with one bacterial isolate at time versus a specific insect. By testing of Bt strains in groups, we identified 28 of 147 Bt isolates as toxic to either diamondback moth, Plutella xylostella (L.), or tobacco hornworm, Manduca sexta (L.). The use of freeze-dried diet and directed pooling of isolates for toxicity testing decreased the number of bioassays required to identify toxic strains by as much as 60% for a given group of isolates. Three of the B. thuringiensis isolates were more toxic to diamondback moth than a standard commercial strain.