DISTRIBUTION OF BARBARA COLFAXIANA (KEARFOTT) (LEPIDOPTERA: TORTRICIDAE) EGGS WITHIN AND AMONG DOUGLAS-FIR CROWNS AND METHODS FOR ESTIMATING EGG DENSITIES

Abstract

AbstractThe spatial and frequency distributions of Douglas-fir cone moth, Barbara colfaxiana (Kearfott), eggs in Douglas-fir trees and stands were determined by dissecting 13 262 conelets collected from 81 trees in three sites and 2 years. There were no consistent trends in egg density associated with crown level or aspect. The frequency distribution of eggs per conelet fitted the negative binomial in three of five site-years but a common k for the negative binomial could not be calculated. Green’s index of aggregation suggested that the cone moth egg distribution was significantly aggregated in each site-year.The optimal number of conelets per tree to sample was determined to be four in forest stands and three in seed orchards. The number of sample trees required for estimating mean egg density with 10% and 20% precision and 90% confidence was calculated for a range of mean egg densities using the method of Kuno. The sample sizes required to estimate a control threshold density of 0.6 eggs per conelet with 10% precision and 90% confidence were very large and would be impractical for operational use. Therefore, a sequential sampling plan was developed for use in seed orchards that would classify cone moth egg densities as either above or below a critical density at which 10% seed loss would be expected.