Abstract
AbstractLarch sawfly larvae, Pristiphora erichsonii (Hartig), naturally reject single needles of newly elongated shoots and consume only tufted foliage from 1 year or older short shoots of tamarack, Larix laricina (Du Roi) K. Koch. Forest entomologists have recognized this unusual feeding behavior for over a century, but not until now has the mechanism been understood. In the bioassasy of unpurified single needle methanol extracts (concn. 1 g needle/ml), 88.5% of the larvae were feeding on the control end of the bioassay twig (solvent only) after 4 h. This was significantly different from a similar bioassay of tufted foliage extract (t-value significant at 0.02 level) and a non-treated control bioassay (distilled water on both ends of bioassay twig) (t-value significant at 0.01 level). In the bioassay of a purified extract of single tamarack needles (TLC fraction 7), 81% of larvae were feeding on the untreated end (t-value significant 0.02). Thin-layer chromatography fraction 7, of eight fractions delineated, alone induced significant feeding inhibition.
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