Interactions of ecdysteroid and juvenoid agonists inPlodia interpunctella (Hübner)

The influence of non‐steroidal ecdysteroid agonists on Indianmeal moth larvae was assessed by rearing last instar larvae on diet treated with RH‐5992 (tebufenozide) or RH‐2485 (methoxyfenozide). Larvae were monitored for effects of the ecdysteroid agonists on weight, metamorphosis and mortality. Larvae treated with either of the ecdysteroid agonists at a concentration of 5 ppm or higher gained less weight and had greater mortality than did larvae reared on control diet. For example, the weights of control larvae increased approximately 400% by day 2, compared with only a 50% increase in weight when the larvae were treated with 25 ppm of RH‐2485 or RH‐5992. Similarly, mortality in control larvae was less than 10%, but was as much as 90–100% in larvae reared on diet treated with one of the ecdysteroid agonists. We also examined the effects of simultaneous treatment with a juvenile hormone (JH) mimic, either methoprene or fenoxycarb. The JH mimics prevented adult emergence, and the larvae continued to feed throughout the month‐long observation period. However, larvae treated with a juvenile hormone mimic gained weight despite the presence of an ecdysteroid agonist in the diet. On diets treated with 0.1 ppm of RH‐2485 or RH‐5992, JH‐treated larvae gained even more weight than did untreated controls. Interestingly, although the addition of a JH mimic to ecdysteroid‐treated diet resulted in increased weight, it did not lead to reduced mortality. In fact, combinations of a JH mimic with 10 ppm RH 2485 or RH 5992 resulted in nearly 100% mortality compared with 40–70% mortality without the JH compounds. These results indicate that JH mimics overcome the inhibitory effects of ecdysteroid agonists on weight gain; however, they also resulted in increased mortality compared with moderate doses of ecdysteroid agonists alone. One specific action of these compounds at the cellular level was noted in that RH 5992 mimicked ecdysteroids by increasing uptake of 14C‐GlcNAc in a Plodia interpunctella cell line, while fenoxycarb was inhibitory. Arch. Insect Biochem. Physiol. 38:91–99, 1998.