The ecology of Cheimophila salicella Hbn. (Lepidoptera: Oecophoridae), a blueberry leaf-tier was studied on high-bush blueberry, Vaccinium corymbosum L., in Richmond, British Columbia. The females frequently laid their eggs in the lichen Xanthoria sp., an oviposition site not previously reported for this species. The possible microclimatic advantages of such behaviour are discussed. In the Field, females required longer than males to complete their 6th instar, so females were usually bigger than males in that instar. The leaf shelter made by the larvae modified their microenvironment in the field. On clear and sunny days, measurements of shelter temperature were 6-7°C above those of ambient air. The shelter temperature remained warmer than the air as long as the incoming radiation levels were high. As the radiation levels dropped, the shelter temperature fell to, or a little below, air temperature. On cloudy days, there was no significant difference between the daily maximum shelter and air temperatures. Under clear skies, the daily amplitude of temperature fluctuations was greater inside the shelter than outside. A laboratory investigation of the effects of such fluctuations on development showed that a large amplitude increased the developmental rate of the lst-4th instars. This increase in rate of development was probably due to an accumulation of extra thermal units (Yeargan 1980) occurring in the large-amplitude regime. However, the high temperature of this regime retarded pupation, and the later instars required longer to complete their development. Overall, larvae in the small and large amplitude regimes required the same amount of time to develop from hatching to pupation. A third regime, "medium amplitude", slowed larval development, probably because the length of its thermophase was longer than that which the insect normally encountered in the field. Fifth- and sixth-instar females took longer than males to complete their development, both in the laboratory and in the field. The larger amplitude regime produced heavier pupae; females were, on average, 12.7 mg heavier than males. The microclimate of the shelter provides the larvae with more degree-days than if they were subjected to ambient air and therefore promotes faster development. Without the extra degree-days provided by the shelter, C. salicella would not be able to complete its larval development before the first lethal autumn frost. / Land and Food Systems, Faculty of / Graduate