Mechanisms contributing epizootics of Bacillus thuringiensis inPlodia interpunctella populations

Abstract: Epizootics of Bacillus thuringiensis Berliner (Bt) among stored product pests wererarely reported in the literature however under specific conditions epizootics do occur in eitherlaboratories or in populations infesting stored products. In order to investigate the mechanismsbehind Bt epizootics including possible correlations between distribution of cry genes to theability of causing epizootics; comparison of cry gene content of a newly isolated Bt strain (BTA),caused several epizootics in laboratory populations of Indianmeal moth, Plodia interpunctella, toother previously reported strains isolated from epizootics in different environmental conditionswas done. Assays were accomplished to evaluate the ability of BTA and B.t. kurstaki HD1 strainsin spreading within laboratory cultures of indianmeal moth. No significant correlation betweencry gene content of epizootic strains and ability to cause epizootics was found, however, cry1I,cry2Ab, and cry9B were present in all epizootic strains. Transmission of Bt from infected larva toanother healthy larvae highly differed in relation to the density of the last instar larvae and thepresence or absence of food. It was shown that transmission was increased with increasing in hostdensity and with more shortage of food. It was concluded that the dynamics of spreading Bt in apopulation mainly related to the biological activity of the pathogen as well as exotic factorsincluding population density and the structure of the environment.