Safety testing of tebufenozide, a new molt-inducing insecticide, for effects on nontarget forest soil invertebrates

Tebufenozide, a new molt-inducing insecticide that mimics the action of ecdysone, is being considered for use to control defoliating lepidoptera in forests in Canada. Soil microcosms, employing substrates and species from the ecosystems in which spraying is likely to occur, were used to evaluate the effects of this compound on soil invertebrates. The forest earthworm (Dendrobaena octaedra Savigny) and four species of Collembola (Folsomia candida Willem, F. nivalis (Packard), Onychiurus parvicornis Mills, and Hypogastrura pannosa Macnamara) were tested. Survival, growth, and reproduction (cocoon production and viability) in the forest earthworm D. octaedra were not affected by exposure to tebufenozide at concentrations up to and including 100x expected environmental concentration (EEC; equivalent to the operational spray rate; 70 g/ha) in leaf litter over a 10-week period. Similarly, population growth over 8-10 weeks in the four species of soil Collembola in LFH material contaminated with tebufenozide at 100x EEC was not affected. Based on the results of these (limited) tests, it therefore appears that, under normal operational conditions, tebufenozide should not pose a hazard to soil invertebrates. The selection of appropriate test species and systems for forestry applications is discussed.