MARKING THE SOUTHERN PINE-BEETLE (COLEOPTERA, SCOLYTIDAE) WITH RUBIDIUM WITHIN LOBLOLLY-PINE FOR DISPERSAL STUDIES

Studies were conducted to improve techniques for the use of elemental marking in dispersal studies of the southern pine beetle, Dendroctonus frontalis Zimmermann. Tissues from host loblolly pines, Pinus taeda L., having diameters at breast height ranging from 15 to 46 cm and the emerging D. frontalis were marked successfully by injection of rubidium (Rb) concentrations based on estimates of bole surface area. A stem-well infusion technique, which is less labor intensive than pressure injections, was found to mark emerging beetles successfully. Use of dimethysulfoxide (DMSO) in RbCl solution did not significantly increase Rb concentration in P. taeda phloem samples or percentage of Rb-marked D. frontalis. Rb was rapidly eliminated by Rb-marked D. frontalis adults when allowed to feed on nonRb-enhanced host tissue, but Rb concentrations remained relatively constant in Rb-marked beetles held without feeding. While this loss of Rb by colonizing D. frontalis would effect use of the elemental labeling technique for subsequent tracking of reemerging adults, it would be relatively unimportant for typical short duration mark-recapture experiments. Rb-marked D. frontalis were successfully recaptured in pheromone-baited traps at distances as far as 1 km from the point of emergence. Recaptures in four cardinal directions indicated a random dispersal pattern. A direct comparison of fluorescent powder and Rb-marking showed both are equally effective. Selection of method will depend on the objectives and experimental design.