Action of RH 5849, a non‐steroidal ecdysteroid mimic, on Plodia interpunctella (Hübner) in vivo and in vitro

Abstract

AbstractWe have examined the effects of RH 5849, a non‐steroidal ecdysteroid mimic, on the growth and development of Plodia interpunctella. When RH 5849 was administered in the diet, larval growth was inhibited in a dose‐dependent manner, while concentrations of 15 ppm and greater were highly toxic. However, the deleterious effects of RH 5849 could be prevented, except at very high concentrations of RH 5849, by the simultaneous administration of the juvenile hormone mimic methoprene. Larvae simultaneously treated with both hormone mimics continued to grow until they attained a size about three times normal. This growth was accompanied by at least one and sometimes two supernumerary molts, whereas, only an occasional supernumerary molt occurred in larvae treated with methoprene alone. In larvae undergoing super numerary molts, wing imaginal discs produced a tanned pupal cuticle, but did not evaginate. When wing discs were cultured in vitro, RH 5849 stimulated evagination and chitin synthesis at concentrations of 10 and 1 μM, respectively. Likewise, RH 5849 stimulated GlcNAc uptake and inhibited cellular proliferation in IAL‐PID2 cells at similar concentrations. These in vitro effects of RH 5849 also were produced by 20‐hydroxyecdysone, but at lower concentrations. We conclude that RH 5849 exhibits molting hormone activity in vivo as well as in vitro. However, the toxicological effects in P. interpuncetella result from action on feeding and growth, rather than molting. Thus, RH 5849 represents a new class of IGR, which will have impact on our understanding of endocrine regulation and open up new avenues for pest control.