Comparative toxiCity of the nonsteroidal eCdysone agonists tebufenozide and methoxyfenozide to early and late larval instars of the white-marked tussoCk moth, Orgyia leucOstigma

Cusson Dallaire, F Dallaire, M Cusson
2017 J. ent. Soc. Ont   unpublished
insecticidal toxicity can vary widely as a function of the developmental stage of the insect being targeted. Here the toxicity of the nonsteroidal ecdysone agonists tebufenozide and methoxyfenozide was evaluated against early and late instars of the white-marked tussock moth, Orgyia leucostigma (J.E. Smith) (lepidoptera: Erebidae), using a droplet-feeding bioassay. On the basis of lD 50 estimates, methoxyfenozide was ~9 and 22 times more effective than tebufenozide in inducing mortality in 1 st
more » ... g mortality in 1 st and 4 th instars of O. leucostigma, respectively. unlike methoxyfenozide, tebufenozide was unable to cause more than 70% mortality in 4 th instars, even at the highest dose tested (1 µg/larva). analysis of the present data suggests that susceptibility of late instar larvae to tebufenozide is significantly compromised whereas that to methoxyfenozide is much less so, which suggests that the mechanism conferring resistance to tebufenozide in late instar larvae is either ineffective or less effective in the case of methoxyfenozide. introduction nonsteroidal ecdysone agonists of the diacylhydrazine family comprise several insecticidal molecules that can induce a precocious and lethal larval molt. Their mode of action involves high-affinity binding to the ecdysone receptor and the persistent expression of molt-related transcription factors (Dhadialla et al. 1998; nakagawa 2005; . Two such compounds, tebufenozide (rH-5992; Smagghe and Degheele 1994) and methoxyfenozide (rH-2485; Carlson et al. 2001) , are highly selective for lepidopterans