EFFECT OF THE ECDYSONE AGONISTS, RH-2485 AND TEBUFENOZIDE, ON THE SOUTHWESTERN CORN-BORER, DIATRAEA-GRANDIOSELLA

The effect of the ecdysone agonists RH-2485 (proposed name methoxyfeno zide) and tebufenozide (RH-5992), was examined on eggs and larvae of t he southwestern corn borer, Diatraea grandiosella Dyar. Both compounds exhibited a concentration-dependent ovicidal activity. More than 95% of eggs died when egg masses were dipped in solutions of 100 or 200 mg liter(-1) of either compound in acetone + distilled water (1 + 1 by v olume). Although some eggs treated with 1 or 10 mg liter-l of the comp ounds hatched, the survival rate was low. Newly hatched larvae were fe d for seven days on an artificial diet containing RH-2485 or tebufenoz ide. The LC50 values were 0.049 mg kg(-1) for RH-2485 and 0 185 mg kg( -1) for tebufenozide, showing that RH-2485 was about four times more a ctive than was tebufenozide. Although increasing the time of exposure to either compound decreased the LC50 value significantly, the relativ e potency of RH-2485 versus tebufenozide was not changed. Newly ecdyse d 4th-instar larvae fed with diets containing 0.125, 0.25 or 0.5 mg kg (-1) RH-2485 or tebufenozide ceased feeding approximately 8 h after ex posure, indicating that larvae had prematurely entered a molting cycle . Larvae treated with RH-2485 ecdysed earlier and died more quickly th an those treated with tebufenozide. Ingestion of sublethal concentrati ons of RH-2485 (0.005 and 0.01 mg kg(-1)) or tebufenozide (0.03 and 0. 06 mg kg(-1)) retarded larval growth, and decreased pupal weight and a dult emergence. Increasing exposure time to tebufenozide tended to inc rease the larval mortality, significantly retarded larval growth, and decreased the mean weights of male and female pupae and adult emergenc e. RH-2485 (0.125 and 0.25 mg kg(-1)) and tebufenozide (0.25 and 0.5 m g kg(-1)) were lethal to newly hatched larvae, even after diets contai ning these compounds were held for 20 days at 30 degrees C under long days (16 h light : 8 h dark). Our results suggest that field trials to assess the potential of RH-2485 and tebufenozide to control D. grandi osella are warranted. (C) 1998 SCI.