Over a century ago Peck (4) observed that open-growing stands of white pine, Pinus strobus L., were subjected to greater weevil damage than were those growing in mixture with, and shaded by, other tree species. This observation, which was later corroborated by Graham (2) and MacAloney (3), suggested possibilities of silvicultural control of the insect by means of plantation growing of white pine in various kinds of mixtures. The results of this work were recently assessed in a review paper by Belyea and Sullivan (1), who concluded that further silvicultural control measures be curtailed until the physical and biological requirements of the insect were defined in terms of measurable factors of the environment. Investigations were carried out (6, 7) to establish the conditions of temperature, light, and moisture favourable for feeding, copulation, and oviposition of the adults, and development of the larvae. The results indicated that P. strobi is well adjusted to the environmental conditions in open stands of white pine, but that the limitations imposed by weather on weevil oviposition might be a major factor contributing to the inability of the insect. to adapt readily to the climate of many shaded stands. The present paper is an attempt to assess the role of weather and the physical characteristics of white pine leaders, hereafter called leaders, in limiting the successful invasion, by the weevil, of white pine stands growing as partially suppressed, understory trees. Emphasis is placed on providing an understanding of the differences in the climate of weevil habitats, adult feeding and oviposition behaviour, and survival of weevil populations in exposed and shaded stands of white pine. In addition, records were obtained for the purpose of forecasting differences in both the timing and amount of such acts as oviposition and feeding in populations in the two habitats.