Action of the nonsteroidal ecdysteroid mimic RH 5849 on larval development and adult reproduction of insects of different orders

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Abstract
Toxicity assays with RH 5849, a nonsteroidal ecdysteroid agonist, indicated a high effectiveness in larval Lepidoptera Spodoptera exempta and Spodoptera littoralis and larvae of the coleopteran, Leptinotarsa decemlineata. 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 induced a premature and lethal larval molt. Hence, mortality also included inhibition of weight gain and feeding, extrusion of the hindgut, loss of hemolymph and an abnormal and lethal pupation, frequently resulting in larva-pupa intermediates. In contrast, RH 5849 had no activity on nymphs of Podisus sagitta and larvae of Locusta migratoria migratorioides. In addition, RH 5849 had a chemosterilizing activity, resulting in total inhibition of oviposition within 2 days of continuous treatment in the lepidopterans S. exempta and S. exigua at doses of ≥ 30 mg/l. On the other hand, deposited eggs of all treatments were viable as compared to controls. Similar effects on reproduction occurred in L. decemlineata.