SPATIAL-DISTRIBUTION OF THE EARLY LARVAE AND COCOONS OF THE PINE SAWFLY NEODIPRION-XIANGYUNICUS (XIAO AND HUANG) (HYM, DIPRIONIDAE) IN CHINA, AND DETERMINATION OF AN OPTIMAL-POPULATION SAMPLING PROGRAM

In this paper we report on investigations into the spatial distribution pattern and optimum field sampling methods for the pine sawfly Neodiprion xiangyunicus, a serious defoliator of Pinus yunnanensis in China. The early instar larvae are mainly distributed on the current year's needles on the lowest shoots at the perimeter of the tree crown, while the cocoons are found mainly in the layer of the soil litter closest to the trunk, these being the optimal sampling sites for maximising the chances of locating sawflies. Using IWAO's Regression Method, both early larvae and cocoons show a between-tree distribution aggregated within colonies, that is, some trees having significantly more sawflies than others. Early larvae also show significant clumping within groups of trees, but cocoons do not. Models expressing the relationship between the proportion of uninfested trees and population density, theoretical sample size and sample accuracy are also presented.