Improved Hydrostatic Pressure Gauge Methods for Measuring Oleoresin Exudation Pressure in Bark Beetle Research

Abstract

Two improved methods for measuring pine oleoresin exudation pressure have been devised. These methods are modifications of the hydrostatic pressure gauge method introduced by Vité (1961). Method 1 describes a modified apparatus and an improved technique for measuring oleoresin exudation pressure from a 11/2-2 inch hole bored into the sapwood of the tree. This method is similar to Vité’s, except for the addition of a filling port and a filling port reservoir. The filling port was found to be essential for obtaining accurate pressure readings on Pinus taeda L. The reservoir was found to facilitate the filling operation, and it also made feasible the measurement of the filling fluid uptake by the tree during the equilibration period. Method 2 describes an apparatus and a technique for measuring oleoresin exudation pressure at the innerbark-wood interface. Since this interface is where bark beetles attack and rear broods, it seems logical to measure oleoresin exudation pressure at this location on the tree when pest-host interrelations are being studied. A discussion of the uses of the methods is given, and some of their advantages and limitations are reviewed.