Canadian Forest Service Publications
Labeling feral spruce budworm populations with rubidium chloride. 2016. MacKinnon, W.E.; Eveleigh, E.S.; Silk, P.J.; Forbes, G. Environmental Entomology 45(2): 427-435.
Available from: Atlantic Forestry Centre
Catalog ID: 39560
CFS Availability: PDF (download)
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Rubidium (Rb) is a trace element that occurs naturally in low concentrations and is easily absorbed by plants, making it a useful tool for labeling insect defoliators, such as spruce budworm (Choristoneura fumiferana Clemens). Balsam fir trees (Abies balsamea (L.) Miller) injected with either 8 or 16 g per tree of rubidium chloride (RbCl) showed quick uptake and distribution throughout the crown, with no negative effects on tree shoot growth or spruce budworm survival and development. Adult spruce budworm that fed as larvae on trees injected with RbCl were clearly labeled, with significantly higher Rb concentrations than the background levels found in adults that fed as larvae on control trees. Rb concentrations in feral spruce budworm adults for both the 8 g (9 mg/g) and 16 g (25 mg/g) per tree treatments were at least five times lower than those in laboratory-reared adults on 1,000 mg/g RbCl diet (125 mg/g); survival, development, pupal weight, sex ratio, and mating status of spruce budworm were not adversely affected by Rb treatment. Egg masses laid by feral females that fed as larvae on Rb-labeled trees were also labeled with Rb. Injecting trees with RbCl is a viable technique for labeling feral spruce budworm populations to help distinguish local populations from immigrants to better evaluate the success of early intervention strategies such as mating disruption.
Plain Language Summary
Rubidium (Rb) is a non-radioactive trace element that occurs naturally and can be found in low concentrations almost everywhere throughout the environment. Balsam fir trees injected with 8 g and 16 g per tree of the Chloride form of Rb (RbCl) showed quick uptake and translocation throughout the current-year foliage with no negative effects on shoot growth. Adult spruce budworm that developed from larvae which fed on balsam fir trees injected with RbCl were clearly marked with Rb because they had significantly higher concentrations than the background levels found in adults that fed as larvae on control trees. These concentrations had no negative effects on spruce budworm survival or development. We conclude that this technique of marking feral spruce budworm may be a useful tool to help measure the success of early intervention strategies for spruce budworm, such as pheromone mating disruption trials, and to help with dispersal studies tracking the movement of populations.
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