Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 10/5/2005
Publication Date: 11/6/2005
Citation: Goh, H., Gelman, D.B., Martin, P.A., Shropshire, A.D., Blackburn, M.B. 2005. Effect of bacillus thuringiensis on the diamondback moth, plutella xylostella. BARC Poster Day. Also used at Society of America Annual Meeting, Ft. Lauderdale FL; November 6-9,2005. Abstract available online. Meeting was post-poned due to Hurricane. Post-poned to 12/15/05-12/18/05
Technical Abstract: Twenty-eight strains of the bacterium, Bacillus thuringiensis (Bt) were screened for toxicity against the diamondback moth (DBM), Plutella xylostella. Bt strains were cultured on agar plates, examined for the presence of crystals and then harvested in water. Samples of Bt spore/crystal preparations, those treated with base (to dissolve the crystal protein) as well as isolated spores were applied to artificial diet prior to placing 2nd instar DBM larvae on the diet. The soluble protein concentration was 2 or 3 times higher in Bt preparations that had been treated with NaOH, centrifuged to remove spores, restored to neutrality with HCl and filtered (0.45µm filter) than in supernatants of initial preparations that were not treated with NaOH. Of the 28 Bt strains tested, seven (IBL #24, 35, 136, 156, 194, 425 and 465) caused high levels of larval mortality after two-three days of feeding. Crude Bt preparations were more toxic (100% mortality at 3 days post-treatment) than samples that were pH-treated, (100% mortality at 6 days post-treatment), probably because of the presence of spores in the former. Bt preparations containing spores but not crystals were only slightly less toxic than crude Bt preparations, i.e., 100% kill was delayed by one or two days. With the addition of crude or pH-treated Bt, DBM mortality decreased in a dose-dependent manner. Crude and pH-treated preparations were stable to three or more weeks of refrigeration; pH-treated Bt was not stable to boiling (therefore, not an exotoxin) or, with the possible exception of Strain #425, to extraction with methanol. Of the seven insecticidal strains, IBL 465 was the most virulent against DBM. Experiments are underway to characterize the toxic Bt-produced factor(s).