Substantial genetic variation in development time is known to exist among mountain pine beetle (Dendroctonus ponderosae Hopkins) populations across the western United States. The effect of this variation on geographic patterns in voltinism (generation time) and thermal requirements to produce specific voltinism pathways have not been investigated. The influence of voltinism on fitness traits, body size, and sex ratio is also unclear. We monitored mountain pine beetle voltinism, adult body size, sex ratio, and air temperatures at sites across latitudinal and elevational gradients in the western United States. With the exception of two sites at the coolest and warmest locations, the number of days required to complete a generation was similar. Thermal units required to achieve a generation, however, were significantly less for individuals at the coolest sites. Evolved adaptations explain this pattern, including developmental rates and thresholds that serve to synchronize cohorts and minimize cold-sensitive life stages in winter. These same adaptations reduce the capacity of mountain pine beetle at the warmest sites to take full advantage of increased thermal units, limiting the capacity for bivoltinism within the current realized distribution. Temperature was not correlated with adult size and sex ratio, and size was greatest in host trees other than lodgepole pine (Pinus contorta Dougl.). Our results provide baseline information for evaluating population responses in a changing climate.

Determining instar distributions from field-collected insect samples is a common problem in insect ecology. We describe a generalized computer program (HeAP) that determines an optimum separation rule based on the distribution of head capsule widths. The program is initiated through visual interaction with the user to determine starting points for separation rules. HeAPthen determines the optimum instar classification rules; estimates of means and standard deviations of headcapsule widths for each instar; estimated number in each instar; and probabilities of misclassification. Application of the program is illustrated by the analysis of 3 data sets of >10,000 observations of headcapsule widths obtained from field collections of larvae of the mountain pine beetle, DendroctonU8 ponderosae Hopkins. This analysis resulted in finding significant differences between larvae collected from different hosts (ponderosa pine, PinU8 ponderosae Lawson, and lodgepole pine, Pinus contorta Douglas variety latifolia Engelmann) and ecological circumstances (outbreak phase and geographic location). These results indicate that caution must be taken when extrapolating published results to new data or from one ecological situation to another.

The sex pheromone of the obliquebanded leafroller, Choristoneura rosaceana (Harris) (Lepidoptera: Tortricidae)