S-methyl-14-C-Orthene was applied to the needles of white spruce and balsam fir twigs in quantities equivalent to a spray of 3, 6, 12 and 16 ounces per acre (oz/acre) and left to penetrate for periods of 1, 3 and 6 days under environmentally controlled conditions. After 6 days, 45 to 60% of the radioactive Orthene was recovered in a surface rinse of the treated needles while 20 to 30% of the radioactivity was recovered in the tissue extracts. Only 1 to 5% had been translocated away from the site of application.
Thin-layer chromatography revealed the presence of six metabolites along with Orthene in tissue extracts of the balsam fir and of five metabolites in white spruce. Three of these metabolites, Including Monitor, were radioactive in the balsam fir extracts while only two, including Monitor, were found to be radioactive in the white spruce extracts. These radioactive metabolites accounted for only 5 to 10% of the total radioactivity recovered in the tissue extracts while l4C-Orthene represented 90 to 95%, regardless of the quantity applied. The surface residue consisted of Orthene only.
When spruce budworms at the fifth instar larval stage were fed surface rinsed balsam fir and white spruce foliage which had been treated with Orthene concentrations equivalent to or higher than 6 oz/acre for 6 days, 100% mortality was recorded after 72 hours while second instars showed 100% mortality after 72 hours of feeding on foliage treated at only 3 oz/acre for 6 days.
No mortality was recorded in fifth instars feeding on foliage that contained only translocated residues while mortality in second instars reached 100% after 72 hours at the higher concentrations of the treatment (12 and 16 oz/acre).
Therefore, Orthene appears to be a good penetrating insecticide with excellent residual toxicity where direct contact between the white spruce and the balsam fir foliage and the chemical has occured but with very little systemic activity per se.