Effects of RH-2485 on larvae and pupae of Spodoptera exigua (Hubner)

A toxicity assay with RH-2485 against larvae of the beet armyworm Spodoptera exigua (Hubner) confirmed time larvicidal potential of this insect growth regulator (IGR). Topical application on last-instar(5th) larvae of RK-2485 resulted in an LD50 of 2.72 ng/larva. indicating an 3-fold higher toxicity as compared to tebufenozide (LD50: 7.61 ng/larva). Intoxicated larvae showed symptoms which were similar to those of tebufenozide: induction of a premature and lethal larval moult, presence of a double head capsule, extrusion of the hindgut and appearance of larva-pupa intermediates. In addition, we performed a series of injections with RH-2485 and tebufenozide an pupae of different ages (0, 2, 4 and 6 days old). Clear disturbances were noted in the metamorphosis process. The wings were conspicuously malformed; however, other external bodyparts such as legs and antennae were not affected. The emerging adults often had problems to discard the pupal exuvium. Concluding, the current assays suggested that RH-2485 has good potential for controlling lepidopterous pests and that wing discs may offer a good tool for evaluating new IGRs that interfere with the ecdysteroid hormone activity.