Effect of the Nonsteroidal Ecdysone Agonists, Methoxyfenozide and Tebufenozide, on the European Corn Borer (Lepidoptera: Pyralidae)

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Abstract
The effect of 2 nonsteroidal ecdysone agonists, methoxyfenozide (proposed name for RH-2485) and tebufenozide (RH-5992), was examined on eggs and larvae of the European corn borer, Ostrinia nubilalis (Hübner). Both compounds were ovicides. More than 90% of eggs died when egg masses were dipped in a solution of 100 ppm methoxyfenozide or tebufenozide in acetone:distilled water (1:1). Although some eggs that were treated with 1 or 10 ppm methoxyfenozide or tebufenozide hatched, the survival rate was low. Test compounds were incorporated into an artificial diet to examine larvicidal effects. Using this technique, methoxyfenozide was 3-7 times more toxic to newly hatched larvae than was tebufenozide. Methoxyfenozide was 184-270 and 147-469 times more toxic to newly hatched larvae than were diflubenzuron and carbaryl, respectively, whereas tebufenozide was 41-68 and 22-75 times more toxic than were diflubenzuron and carbaryl, respectively. Methoxyfenozide was toxic to 3rd instars with the LC50 value being ≈2 times higher than it was for newly hatched larvae. Methoxyfenozide (0.125 and 0.25 ppm) and tebufenozide (0.25 and 0.5 ppm) were lethal to newly hatched larvae, even after diets containing these compounds were held for 20 d under long days (16:8 [L:D] h) at 30°C. Tebufenozide applied at 0.016 and 0.031 ppm to larvae inhibited larval growth, delayed pupation, and decreased adult emergence. Methoxyfenozide applied at 0.063, 0.125, 0.25, and 0.5 ppm to newly ecdysed 4th instars caused them to stop feeding ≈8 h after exposure and induced a premature and lethal molting cycle. Methoxyfenozide and tebufenozide are potential insect growth regulators for controlling O. nubilalis.

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