ACTION OF THE NONSTEROIDAL ECDYSTEROID MIMIC RH-5849 ON LARVAL DEVELOPMENT AND ADULT REPRODUCTION OF INSECTS OF DIFFERENT ORDERS

Toxicity assays with RH 5849, a nonsteroidal ecdysteroid agonist, indi cated a high effectiveness in larval Lepidoptera Spodoptera exempta an d Spodoptera littoralis and larvae of the coleopteran, Leptinotarsa de cemlineata. Larvae of Mamestra brassicae were moderately susceptible; last larval instars of Spodoptera exigua and Galleria mellonella both showed even a lower sensitivity. After topical application, RH 5849 in duced a premature and lethal larval molt. Hence, mortality also includ ed inhibition of weight gain and feeding, extrusion of the hindgut, lo ss of hemolymph and an abnormal and lethal pupation, frequently result ing in larva-pupa intermediates. In contrast, RH 5849 had no activity on nymphs of Podisus sagitta and larvae of Locusta migratoria migrator ioides. In addition, RH 5849 had a chemosterilizing activity, resultin g in total inhibition of oviposition within 2 days of continuous treat ment in the lepidopterans S. exempta and S. exigua at doses of greater -than-or-equal-to 30 mg/l. On the other hand, deposited eggs of all tr eatments were viable as compared to controls. Similar effects on repro duction occurred in L. decemlineata.