Infection of Popillia japonica larvae with heat-activated spores of Bacillus popilliae

Abstract

Maximum outgrowth of spores of Bacillus popilliae resulted after they were heated at 50°C, but outgrowth diminished as the temperature was increased to 80°C. Although outgrowth was limited and often variable, infectivity was predictably influenced by heat activation of spores. The greatest number of Popillia japonica larvae (92.6%) were infected by injection of one million spores per larva heated at 50°C. By contrast, maximum infection from the same number of unheated spores was only 38.9%. Infectivity of spores heated at 60°C and at 70°C generally was intermediate between these values; heating at 80°C afforded minimal infectivity. Apparently infectivity depends on the efficacy of spore outgrowth which, in turn, is influenced by appropriate heat treatment.