During the course of a study of the bionomics of the pitted ambrosia beetle, Corthylus punctatissimus Zimm., in southern Ontario in 1959, the method of overwintering fungal spores and their transmission from brood galleries to healthyplants by the beetle was determined. It was found that a structure exists, in the prothorax of males of C. punctatissimus, for this purpose. The spores are stored in a long, folded tube on each side adjacent to the prothoracic wall. The opening of each tube is in the prothoracic coxal cavity and is opened or closed by a process on the coxa. Since there are no muscles attached directly to the tubes, the spores are probably discharged by the squeezing action (on the tubes) of the retracted head against the prothoracic wall. The inside surface of the tubes is very smooth and glossy, producing a minimum of resistance to the flow of spores. No evidence was found of any comparable structure for storing spores in the females of C. punctatissimus.