Intestinal bacteria affect growth of Bacillus thuringiensis in larvae of the oriental tea tortrix, Homona magnanima Diakonoff (Lepidoptera : Tortricidae)

Spores and parasporal crystals of a Bacillus thuringiensis serovar aizawai were fed to fifth instar larvae of the oriental tea tortrix, Homona magnani ma, that had been reared aseptically or that had been reared normally. Viab le cell numbers of B. thuringiensis and other bacteria in H. magnanima larv ae mere estimated by homogenization of samples and dilution plating on pept one-polymyxin agar medium for B. thuringiensis cells and on nutrient agar m edium for the other bacterial cells. B, thuringiensis did not grow in the l arval cadavers of normally reared H. magnanima while bacteria other than B. thuringiensis grew rapidly. In contrast, B. thuringiensis within the larva l cadavers of aseptically reared H. magnanima. grew and increased 20 times. The bacteria other than B. thuringiensis from the sample homogenates of no rmally reared larvae that were fed on B. thuringiensis-treated diets had th e same characteristics as the bacteria isolated from the guts of healthy H. magnanima larvae, which were putatively identified as Streptococcus spp. a nd Staphylococcus spp., typical intestinal bacteria of insects. The results strongly suggest that intestinal bacteria influence the growth of B. thuri ngiensis in the larvae. (C) 2000 Academic Press.