The phenology of white spruce and the spruce budworm in northern Alberta

Studies on the development of spruce budworm (Choristoneurafumiferana (Clem.)) on white spruce (Piceaglauca (Moench) Voss) were conducted in northern Alberta in 1969 and again in 1990. The phenology of this insect and its host were described using stochastic models. The synchrony between host and insect is remarkable; each instar specializes on a particular shoot developmental stage, with feeding ceasing when shoots start to become lignified. There was little difference between estimates for the duration of the feeding stages of populations observed in 1969 and those studied in 1990. The models also described the variation that might be encountered in treatment blocks when operational considerations of scheduling treatments over large areas are a concern. When measured in degree-days, the initiation of emergence is later and the postemergence period is shorter in these northern populations than those reported for populations in southern Canada on the same host. The nature of the seasonal controls of spruce budworm development is unknown, but the differences between northern and southern populations of the insect suggest that knowledge of these controls will be invaluable if the status of these populations is to be evaluated under climate-change scenarios. The synchrony with host development and the short duration of the early instars together with their habit of feeding in protected locations under bud caps suggest that aerially applied controls that depend on the insect acquiring lethal doses through ingestion have to be targeted to the last, sixth, instar. These observations also suggest that population suppression, rather than foliage protection, would be the better control strategy.