Sublethal Effects of Flufenoxuron, Fipronil and Methoxy-fenozide on Spodoptera litura (Fabricius)

Three insecticides, viz. flufenoxuron, fipronil and methoxyfenozicle, having different modes of action, were evaluated for their chronic effects at sublethal concentrations (LC₁₀to LC₂₅for neonate larvae) on development of second-instar larvae of common cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) by incorporation in semiisynthetic diet. All the three insecticides at 0.5 to 2.5 ppm a.i. have extended the larval life to 30 d compared to only 15 d in control. Cumulative mortality up to pre-pupal stage was 26 to 32% due to flufenoxuron and fipronil and over 70% due to methoxyfenozide. Most of the insects that survived after the prolonged larval stage was dead at the next moult. Twenty-four hours feeding by last-instar larvae on castor leaves, sprayed with sublethal concentration (LC₂₅) of the three insecticides, adversely affected the fecundity and fertility of the moths. Flufenoxuron, fipronil and methoxyfenozide caused 34%, 12.8% and 17.7% reduction in fecundity, respectively. Chronic effect of flufenoxuron is more pronounced on reproductive parameters, especially fecundity.