Toxicity of the ecdysone agonist tebufenozide to codling moth (Lepidoptera: Tortricidae)

The ecdysone agonist tebufenozide (RH-5992) has ovicidal, larvicidal but no adulticidal activity against codling moth, Cydia pomonella (L.). The toxic ity to eggs varied with the application and with the substrate on which egg s were laid. On apple leaves treated in a spray tower, the ovicidal activit y of tebufenozide was approximate to 30 times greater when eggs where laid on top of the residue than with topical application of eggs after they were laid (LC(50)s of 4.35 and 123.8 ppm, respectively). Eggs laid on apples tr eated in a spray tower were not affected by tebufenozide residue. However, tebufenozide had low residual toxicity to eggs (LC50 = 117.47 ppm, flat dos e-response line) when fruit was dipped instead of sprayed, suggesting some residual control on the fruit surface with airblast applications in the fie ld. The LC(50)s for neonate larvae feeding on treated apples and on treated artificial diet were 16.08 and 0.22 ppm, respectively. In tests with artif icial diet, susceptibility to tebufenozide decreased with larval age. Bioas says with artificial diet established reference lines for tebufenozide susc eptibility in different instars. Contact exposure of neonates to tebufenozi de residue on treated leaves or on a plastic surface caused mortality in la rvae. Larval mortality increased with the duration of contact exposure. The effect of contact exposure on larval mortality was greater on treated appl e leaves than on a treated plastic surface. Tebufenozide had no direct toxi city to adults (both sexes) and their longevity was not affected. Because o f its ovicidal and larvicidal activity there is more flexibility in terms o f spray timing with tebufenozide than with other insect growth regulators ( e.g., diflubenzuron, fenoxycarb) which are primarily effective against the egg stage.