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Sampling methods and population prediction in Lambdina fiscellaria lugubrosa (Lepidoptera: geometridae) in British Columbia Liang, Qiwei


Outbreaks of Lambdina fiscellaria lugubrosa in British Columbia have always been preceded by a rapid population growth. Sampling methods and population prediction models are needed to provide forest managers with the capability of monitoring and predicting populations of the insect. I sampled eggs, larvae, pupae and adults of Lambdina fiscellaria lugubrosa at various locations in the province of British Columbia from 1992 to 1994. Population estimates of eggs and larvae, directly obtained from habitat units, were fitted to theoretical spatial distribution and mean - variance models. Sampling plans, based on fixed sample size, sequential sampling, and binomial sampling methods, were developed. Pupae were sampled with burlap traps of different designs. Because more pupae were trapped in two or three layers of burlap than in a single layer, traps with at least two layers are recommended for future use. The strong linear relationship of pupal density between burlap traps and open tree bark units validated the use of burlap traps as a sampling tool. Spatial continuity of larval and adult densities was found along forest roads, although the range and magnitude of the spatial dependence varied significantly between years and among sites. Also, larval and adult densities along the road were closely related to those within the stands. The results showed a great potential of roadside sampling for the management of this insect. Regression models showed strong quantitative relationships of population estimates between successive life stages, which can be used to predict population density. Defoliation prediction was conducted with discriminant analysis, in which defoliation classes were related to insect population estimates and tree DBH. Like many other studies in insect sampling, the insect samples were non-random in this study. Randomization tests were used to validate results from conventional statistical analyses and to examine the general necessity of using randomization tests in insect sampling. The results suggested that non-random insect samples do not seriously hamper the use of conventional statistical analyses. The implications of this study to the management of western hemlock looper and other forest insects were discussed.

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