The interaction between Plodia interpunctella Hbn., parasites and predators and Bacillus thuringiensis Berl. has been investigated. Experiments with the parasite Bracon brevicornis Wesm. previously fed during the larval instar on treated host larvae of P. interpunctella, showed significant reduction in the egg production. The egg incubation and larval duration of the parasite were not affected except at the highest concentration (500 mu-g). Percentage of formed cocoons was significantly reduced at all tested concentrations. The longevity of either sex, on the other hand, was also reduced. The percentage of hatching among the deposited eggs, significantly decreased with the increase of concentration. Investigations with adult parasite fed on treated honey solution showed a significant reduction in the number of eggs deposited, hatching among the deposited eggs, percentage of formed cocoons, the percentage of adult emergence and the longevity of the female parasite, was also reduced with the increase of concentrations. With respect to the predator Xylocoris flavipes (Reuter), it was found that the number of consumed host larvae of P. interpunctella by nymphs of the predator decreased with the increase of concentration of delta-endotoxin present on the larval food. The nymphal duration was prolonged as the concentration increased from 32-500 mu-g/g of diet. On the other hand, the longevity of male predator was shortened while that of female was not affected. The consumption of prey larvae by one couple of the predator was reduced only at higher concentrations (250-500 mu-g). The egg production and hatchability of eggs were also reduced. Studies with the adult stage of the predator showed similar effects with respect to the longevity of the female adults. Also the average consumption of one couple was reduced and an obvious effect on egg production was detected but in varying degrees correlated with the concentration. The hatching of eggs increased as the concentration used decreased.