Possible Role of Plant Allelochemical in Clearance of Bacteria from the Gut of Spruce Budworm, Choristoneura fumiferana

Field results, using Bacillus thuringiensis delta-endotoxin in controlling spruce budworms, Choristoneura fumiferana, are far less satisfactory than those from the laboratories The role of septicemia has also been shown to be important in mortality. However its relationship with insect diet has not been studied. Insect gut juice from spruce budworm fed on balsam foliage inhibited bacterial growth. Such activity has not been observed in the gut juice from insects fed on artificial diet. Moreover, when bacteria were given to the insects orally, and the insects then fed on balsam foliage overnight, little or no bacterial colonies could be detected in their gut juices in the tryptic soy agar plates. Such bacterial growth inhibition activity could also be found in the water extract of balsam foliage, and was suggested to be due to tannins. This result explains the role of allelochemicals affecting septicemia in spruce budworms, and hence the efficacy, when using Bacillus thuringinesis delta-endotoxin as a biologic control agent.