Canadian Forest Service Publications
Comparative toxicity of the nonsteroidal ecdysone agonists tebufenozide and methoxyfenozide to early and late larval instars of the whitemarked tussock moth, Orgyia leucostigma. 2017. Dallaire, F.; Cusson, M. J. ent. Soc. Ont. 148: 6-12.
Issued by: Laurentian Forestry Centre
Catalog ID: 38835
Availability: PDF (request by e-mail)
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 LD50 estimates, methoxyfenozide was ~9 and 22 times more effective than tebufenozide in inducing mortality in 1st and 4th instars of O. leucostigma, respectively. Unlike methoxyfenozide, tebufenozide was unable to cause more than 70% mortality in 4th 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.
Plain Language Summary
In this study, the researchers assessed the toxicity of two insecticides (tebufenozide and methoxyfenozide) on the whitemarked tussock moth. Methoxyfenozide was found to be 9 to 22 times more efficient for killing this insect’s larvae at the second stage and fourth stage of its development, respectively. Conversely, tebufenozide did not kill more than 70% of larvae at the fourth stage, even when used at high doses.
In light of these results, the researchers concluded that the resistance-inducing mechanism is either less efficient in older larvae for tebufenozide or totally inefficient for methoxyfenozide.