Instar Discrimination of Field-Collected Larvae through Analysis of FrequencyDistribution Curves of Head Capsule Widths Using the Program PeakFit

摘要

A new method is described to analyze frequency distribution curves using acommercial program PeakFit-TM. It is illustrated with frequency distribution data of head capsule widths of the western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), a species that exhibits developmental polymorphism. Analyses using PeakFit were capable of accounting for better than 99 percent of the number of head capsules in data sets of field-collected larvae and could classify from 50 to 73 percent to instar sets. Additional resolution is possible when the influence of parasitism on the head capsule width of the host is known. Such a possible influence was considered for C. occidentalis and, if the assumptions made were valid, up to 85 percent of samples could be characterized to instar. The advantage and disadvantages of using PeakFit are discussed.