A SAMPLING DESIGN FOR WITHIN-TREE LARVAL POPULATIONS OF THE MARITIME PINE SCALE, MATSUCOCCUS-FEYTAUDI DUC (HOMOPTERA, MARGARODIDAE), AND THE RELATIONSHIP BETWEEN LARVAL POPULATION ESTIMATES AND MALE CATCH IN PHEROMONE TRAPS

Sampling procedures for estimating within-tree populations of second-s tage larvae (L2) of Matsucoccus feytaudi Duc., infesting maritime pine (Pinus ponaster Ait.), were investigated. These included random sampl ing without replacement, and systematic sampling with and without a li near model. The relative precision of the sampling was affected by the number, size, and bark thickness of the sample units. Because of symm etrical vertical distribution of within-tree populations, systematic s ampling with a linear model did not increase precision when compared w ith simple systematic sampling. Sampling can be profitably reduced to below the crown portion of the bole, after removal of the part with ei ther smooth or very thick and pyramidal bark. Counting L2 exuviae in t he upper 10 cm of each 20-cm-long log, using one in every three logs, provided a relative precision of about 40%. The numbers of male M. fey taudi caught in sticky traps baited with 5 or 30 mu g of synthetic phe romone were compared with the numbers of L2 estimated according to the sampling method previously developed. There was a significant positiv e correlation between number of scales caught and L2 estimates, at the level of individual trees for the lower dose lures, and at the level of groups of trees for the higher dose lures, used in 20-year-old stan ds. Large captures in younger, weakly infested stands were related to a possible immigration of flying scale insects.