ACTION OF A NOVEL NONSTEROIDAL ECDYSTEROID MIMIC, TEBUFENOZIDE (RH-5992), ON INSECTS OF DIFFERENT ORDERS

The nonsteroidal ecdysteroid agonist tebufenozide (RH-5992) was tested on larval stages of a number of lepidopteran species by topical appli cation and by feeding on treated leaves. LC50 values in the range 0.03 -0.10 mg litre -1 were obtained for third to sixth instars of Spodopte ra exempta (Walker) when insects were fed on leaves dipped in aqueous emulsions of the compound, while first to fifth instars of Spodoptera exigua (Hubner) were less susceptible (LC50 values in the range 2.5-10 .5 mg litre-1). When insects were topically treated, susceptibility of last-instar larvae of Lepidoptera tested decreased in the order Spodo ptera exempta, Mamestra brassicae L., Spodoptera littoralis (Boisd.), S. exigua and Galleria mellonella L. Tebufenozide induced a premature and lethal larval moult in larval Lepidoptera within 24 h of treatment . Most larvae died in their old larval cuticle. Other aberrations incl uded inhibition of weight gain and feeding, extrusion of the hindgut, loss of hemolymph and an abnormal and lethal pupation. In contrast, te bufenozide at similar doses/concentrations had no activity on larval i nstars of Leptinotarsa decemlineata (Say) and Diabrotica virgifera vir gifera (LeConte), nymphs of Podisus sagitta (F.) and larvae of Locusta migratoria migratorioides (R. & F.). It had a chemosterilizing activi ty in S. exigua, resulting in a total inhibition of oviposition within two days of continuous treatment at doses of greater-than-or-equal-to 10 mg litre-1. On the other hand, all deposited eggs were viable. Sim ilar effects on reproduction occurred in L. decemlineata, but at highe r concentrations.