GENERAL PROGRAM FOR DETERMINING INSTAR DISTRIBUTIONS FROM HEADCAPSULEWIDTHS - EXAMPLE ANALYSIS OF MOUNTAIN PINE-BEETLE (COLEOPTERA, SCOLYTIDAE) DATA

Determining instar distributions from field-collected insect samples i s a common problem in insect ecology. We describe a generalized comput er program (HCAP) that determines an optimum separation rule based on the distribution of headcapsule widths. The program is initiated throu gh visual interaction with the user to determine starting points for s eparation rules. HCAP then determines the optimum instar classificatio n rules; estimates of means and standard deviations of headcapsule wid ths for each instar: estimated number in each instar; and probabilitie s of misclassification. Application of the program is illustrated by t he analysis of 3 data sets of >10,000 observations of headcapsule widt hs obtained from field collections of larvae of the mountain pine beet le, Dendroctonus ponderosae Hopkins. This analysis resulted in Ending significant differences between larvae collected from different hosts (ponderosa pine, Pinus ponderosae Lawson, and lodgepole pine, Pinus co ntorta Douglas variety latifolia Engelmann) and ecological circumstanc es !outbreak phase and geographic location). These results indicate th at caution must be taken when extrapolating published results to new d ata or from one ecological situation to another.