Dissection and rearing studies of second-year cones disclosed six species of insects associated with the seeds and cones of singleleaf pinyon pine. Those most commonly encountered were: Dioryctria sp. probably albovittella Hulst, Conophthorus monophyllae Hopkins and Pineus coloradensis Gillette. The three remaining species were of lesser importance. These included the gall midge, Asynapta sp., a minor cone pest and two parasites, one of C. monophyllae, Acerocephala atroviolacea Crawford and an unidentified parasite of Dioryctria, of the family Ichneumonidae. D. sp. probably albovittella was regarded as the major insect destroying cones and seeds of P. monophylla in this study. During the 1976 growing season it attained a maximum level of 29 percent infestation. C. monophyllae occurred less frequently in this study, but probably has a higher potential for destruction in years of poor cone crops or high cone beetle populations. P. coloradensis caused negligible damage to seeds and cones, but was encountered frequently. Early in the growing season it infested a maximum of 38 percent of the cones.