Gnathotrichus retusus is primarily univoltine with a minor fraction of the population taking more than one year to complete the life cycle. From the spring to the summer, the development of brood from egg to adult took about 40 days or more in Douglas-fir logs. Brood production was significantly related to the gallery length. Boring activities were not consistently related with temperature, shifting from shallow sapwood to deep sapwood over time. Fungal staining was usually limited to the wood near the gallery entrance, and became darker in colour over time beginning in June. Abandonment of some galleries mainly occurred in June and July by females, and was probably induced by high temperatures. G. retusus preferred Douglas-fir stumps to western hemlock stumps, but both host tree species were equally suitable for G. retusus brood development. Significant differences were found among individual Douglas-fir and western hemlock stumps in attack density and brood production. Within a stump, attack density and brood production for Douglas-fir, and attack density for western hemlock increased from the stump top to the bottom. G. retusus emergence from Douglas-fir and western hemlock stumps and G. retusus and G. sulcat us flights began in late April when the daily maximum temperature reached 13.5°C, and peaked in late May. Brood emergence of G. retusus ceased, with rare exception, in late June. G. retusus had only one big peak flight while G. sulcatus had a small second peak flight in late July. Seasonal flights ceased in October when weekly mean maximum temperatures dropped below 15°C. Brood emergence, seasonal flights, and the sex ratios of brood ready to emerge and captured flying beetles were positively correlated with maximum temperature. G. retusus had a bimodal diurnal flight rhythm: a very small morning flight and a much larger dusk flight. Light intensity seemed to be a major stimulus in initiating the flight. However, diurnal flight might also be influenced by both temperature and relative humidity. Both G. retusus and G. sulcatus of both sexes responded significantly to ethanol or their own aggregation pheromones, (+)-sulcatol and (±)-sulcatol respectively, and ethanol was a synergist of (+)-sulcatol for G. retusus of both sexes. Alpha-pinene was neither a primary host attractant nor a synergist of aggregation pheromones. The sex ratios (female/male) of both species increased significantly from less than one for host chemicals alone to above one for treatments including aggregation pheromones. The sex ratio of G. sulcatus increased with increases in release rates of (±)-sulcatol. / Forestry, Faculty of / Graduate

A study has been conducted with the objectives of (1) identifying weevils and their parasitoids emerging from infested lodgepole pine leaders, (2) determining emergence patterns of hosts and their parasitoids, and (3) obtaining further information on the biologies of the terminal weevils and their natural enemies in British Columbia. The major experiments and biological observations were carried out in young spaced lodgepole pine, (Pinus contorta Dougl. var. latifolia Engelm.), stands at Ellis creek, near Penticton, B.C. A total of 1046 infested leaders were collected. One-third of the terminals were dissected and the numbers of weevils and parasitoids at developmental stages were recorded. The remainder of the leaders were set up for individual rearing. Observations were also made on the feeding and ovipositional behavior of the weevils. Feeding habits of the parasitoids were also studied. Dissections showed that a few adult weevils emerge in the fall of the year of attack. The majority of adults overwinter as larvae but pupation also may occur prior to winter. In addition, dissections indicated that parasitism plays an important role in larval mortality of weevils. Weevils which emerged in the laboratory were identified as being of the following species: Pissodes terminalis Hopping, Magdalis gentilis LeC. and Cylindrocopturus sp. (COLEOPTERA: Curculionidae). M. gentilis is the first weevil species to emerge, in late May. This emergence is followed by that of P. terminalis from early June through mid-July, while Cylindrocopturus sp. emerges from early June through mid-July. P. terminalis attacks the current year's leaders, whereas adult M. gentilis and Cylindrocopturus sp. feed on foliage. All three weevil species utilize lodgepole pine terminal shoots for breeding. Larval feeding under the bark almost always results in the death of the terminal. The terminal weevils have a complex of natural enemies in British Columbia. Parasitoids belong to six families of the order Hymenoptera. The pteromalid Rhopalichus pulchripennis Crawford is the most widely distributed parasitoid species in the province. Two species of Eurytoma (Eurytomidae) ranked second in abundance. Emergence patterns of adult parasitoids are closely synchronized with that of their hosts. Parasitoids were observed feeding on pollen of flowering weeds in the field. This observation suggests that natural parasitoid populations could be enhanced by cultivating lupin, Lupinus sp., in lodgepole pine stands. It was concluded that every effort should be made to minimize weevil numbers in order to prevent formation of crooks, forks and stag-heads. Early emergence of M. gentilis suggests that leader clipping projects should be carried out by early spring. Further research is recommended to ensure correct association between parasitoids and host weevil species and to develop or establish methods for preservation of parasitoids for clipped leaders for release in the forest. / Forestry, Faculty of / Graduate