Interactions between Bacillus thuringiensis subsp. kurstaki HD-1 and midgut bacteria in larvae of gypsy moth and spruce budworm |
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Authors: | Kees van Frankenhuyzen Yuehong Liu Amanda Tonon |
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Institution: | Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, 1219 Queen Street East, Sault Ste. Marie, Ontario, Canada P6A 2E5 |
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Abstract: | We examined interaction between Bacillus thuringiensis subsp. kurstaki HD-1 (Foray 48B) and larval midgut bacteria in two lepidopteran hosts, Lymantria dispar and Choristoneura fumiferana. The pathogen multiplied in either moribund (C. fumiferana) or dead (L. dispar) larvae, regardless of the presence of midgut bacteria. Inoculation of L. dispar resulted in a pronounced proliferation of enteric bacteria, which did not contribute to larval death because B. thuringiensis was able to kill larvae in absence of midgut bacteria. Sterile, aureomycin- or ampicillin-treated larvae were killed in a dose-dependent manner but there was no mortality among larvae treated with the antibiotic cocktail used by
Broderick et al., 2006] and Broderick et al., 2009]. These results do not support an obligate role of midgut bacteria in insecticidal activity of HD-1. The outcome of experiments on the role of midgut bacteria may be more dependent on which bacterial species are dominant at the time of experimentation than on host species per se. The L. dispar cohorts used in our study had a microflora, that was dominated by Enterococcus and Staphylococcus and lacked Enterobacter. Another factor that can confound experimental results is the disk-feeding method for inoculation, which biases mortality estimates towards the least susceptible portion of the test population. |
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Keywords: | Bacillus thuringiensis subsp kurstaki HD-1 Enterococcus Staphylococcus Lymantria dispar Choristoneura fumiferana Pathogenicity |
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