Marking forest insects: evaluation of two systems for the systemic introduction of rubidium into Douglas-fir trees

Abstract

Mauget® and Medicap® systems were evaluated for the systemic introduction of RbCl into Douglas-fir trees in the University of British Columbia Research Forest, Maple Ridge, B.C. Single, double, and triple rings of devices were placed on trees and Rb levels in foliage were monitored every 2 weeks for 8 weeks. At 8 weeks, trees were felled and phloem and sapwood samples were collected. Wounding associated with the injection devices was evaluated. Triple ring Mauget® injectors gave best results with more than 1890 ppm Rb in leader foliage. Rb levels were evenly distributed by height and aspect throughout the study trees. Highest levels of Rb were found in phloem tissue and these were often 3 times those in adjacent sapwood. Greater wounding, measured by failure to lay down current year springwood, was associated with the Medicap® implants. Some of this was probably caused by our failure to fully insert and thereby seal the implants properly in the tree, and a second factor may have been Rb toxicity as the capsule and RbCl crystals dissolved. A single ring of Mauget® injectors and a double ring of Medicaps® resulted in foliar Rb concentrations high enough for labelling of defoliating insects. High phloem levels of Rb suggest that bark beetles feeding on these trees would also be well labelled.