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Analysis of some factors influencing the distribution and abundance of the poplar and willow borer (Sternochetus lapathi (L.)) on scouler willow (Salix scouleriana Barratt). Safranyik, Laszlo

Abstract

A study was carried out during the summer of 1963 to determine the importance of some factors influencing the distribution and abundance of S. lapathi (L), on scouler willow, on Spur 17 of the University Research Forest, near Haney. The investigation was done through the observation and sampling of populations in the field, supported by laboratory experiments designed to determine the number of larval instars and the rate of dispersion by means of walking. The following items were investigated: 1) Number of larval instars, 2) Inter- and intra-tree differences in insect mortality, 3) Differences in within-tree distribution of different life stages, 4) Differences in between-tree distribution of combined, adult-plus-pupal stages and of larval instars, 5) Rate of dispersion of starved and fed beetle populations, 6) Influence of tree height, d.b.h., age, and number of crevices per square inch of bark area on infestation intensity and, 7) Sampling method to determine larval population levels. Five larval instars were found for the larval stage of the weevil. Tree height, d.b.h., age, and number of infestations per tree had no marked influence on trend of weevil mortality. Mortalities of first and second instar larvae were higher within the lower three foot trunk sections of sample trees than those in the higher sections of the trunks. The vertical distribution of larval galleries had no marked influence on the mortality of the other life stages of the weevil. Mean infestation height of combined, adult plus pupal stages was significantly lower (significant at 0.05 level) than that for the combined larval stages. Starved beetles dispersed more than their fed counterparts. D.b.h., and tree height were the most important variables in determining the intensity of infestation on an individual tree. A two-stage sampling method was developed to ascertain larval population levels.

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