: Toxicity assays with tebufenozide, the Ðrst commercial non-steroidal ecdysteroid agonist, against a laboratory strain of the beet armyworm, Spodoptera exigua (Hu bner), demonstrated the promise of this new compound for the control of this important pest. Experiments to select insects artiÐcially from the laboratory strain by continuous exposure of larval instars to corresponding LC 25 doses of tebufenozide for over 12 generations 14È15 months), (G 0 ] G 12 : revealed no loss in susceptibility to the insecticide for up to Ðve generations. Moreover, retention and fate of 14C-labelled tebufenozide were investigated using larvae from the selection experiments and the results compared with G 6 those for the susceptible larvae. In addition, piperonyl butoxide, an inhibitor (G 0 ) of monooxygenases, when ingested by larvae along with tebufenozide, increased the susceptibility of intoxicated larvae to this ecdysteroid agonist, indicating its oxidative metabolism in Spodoptera larvae.1998 Society of Chemical ( Industry.

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