The Effect of δ-Endotoxin of Bacillus thuringiensis on the Gut Movements of the Silkworm, Bombyx mori

Peroral administration of toxic crystals of Bacillus thuringiensis to larvae of the silkworm, Bombyx mori, resulted in the inhibition of rhythmic contractile movements of the midgut.The paralysis began in the second-fourth of the midgut. The affected region was extended to the entire midgut except for the posterior end. Recovery from the midgut paralysis occurred in larvae which survived the exposure to the toxin. The time interval intervening between the administration of the toxin and the midgut paralysis became shorter as the dose increased. The interval varied depending on the subspecies of B. thuringiensis which produced the toxic crystal. The administration of activated toxin resulted in an earlier manifestation of paralysis in a wider portion of the midgut. The optimum condition for activating the toxin differed with the different subspecies of B. thuringiensis. The toxin caused midgut paralysis in the presence of tetrodotoxin.