Ecological studies of Hylobius radicis Buch., H. Pales (HBST.) and Pissodes approximatus Hopk. (Coleoptera: Curculionidae) in southern Ontario

Three native weevils have become increasingly important in recent years in stands of planted pines in southern Ontario. The pine root collar weevil, Hylobius radicis Buch., breeds in the root collar of healthy pines, killing over 90% of the trees in some plantations. The pales weevil, H. pales. (Hbst.), and the northern pine weevil, Pissodes approximatus Hopk., are important because the adults, feeding on the tender bark of twigs and small branches of healthy pines kill the branches or even the whole tree. The life histories and bionomics of the three species were determined from natural populations in the field and colonies in the insectary. These studies were facilitated by a special technique devised for rearing the weevils permitting continuous observations of larval and pupal development and periodic measurment of body size and larval feeding. Stand density is the chief factor regulating populations of H. radicis, fostering high populations in the dense stands of plantations, and excluding the insect from sparser natural stands. Scots pine is evidently more susceptible than red pine to H. radicis where the two tree species grow together, but the presence of Scots pine increases the infestation in red pine. Availability of suitable breeding material in the form of numerous stumps left after cutting is the factor governing the number of H. pales and P. approximatus. The implications for forestry consist of recommendations to avoid pure dense stands especially of exotic species, and to practice forest sanitation in cutting operations.Science, Faculty ofZoology, Department ofGraduat