The occurrence of selected late-instar lepidopteran larvae, such as fall armyworm, Spodoptera frugiperda (J. E. Smith), on Bacillus thuringiensis Berliner (Bt) cotton, Gossypium hirsutum (L.), plants has become a common problem in recent years. In some instances, there is a need to manage these infestations with supplemental foliar insecticide applications. The objective of these studies was to evaluate the efficacy of selected insecticides (chlorantraniliprole, flubendiamide, lambda-cyhalothrin, novaluron, and spinetoram) against fall armyworm in transgenic Bt (Bollgard II®) and non-Bt (conventional) cotton. Bollgard IIplants were sprayed with reduced (one-half of full)) rates of insecticides and conventional cotton was sprayed with recommended (full) rates of the same products. Plant terminal leaves and bolls were removed from sprayed and non-sprayed (control) field plots, returned to the laboratory, and infested with a single third-instar fall armyworm. Larval mortality ranged from 30.0 to 95.0% and from 22.5 to 82.5% on insecticide-sprayed (reduced rates) Bollgard II and insecticide-sprayed (full rates) conventional terminal leaves, respectively, 3 d after infestation. Fall armyworm survivorship did not differ on insecticide-sprayed Bollgard II plant tissue compared to that for the same insecticide used on conventional plants. Reduced insecticide rates on Bollgard II cotton did not negatively affect efficacy of any insecticide used compared to full rates on conventional cotton. Insecticide-sprayed Bollgard II and insecticide-sprayed conventional bolls caused fall armyworm mortality ranging from 5.0 to 80.0% and from 17.5 to 80.0%, respectively, 3 d after infestation. These same insecticide treatments produced fall armyworm mortality on Bollgard II(55-100%) and conventional bolls (52.5-100%) at 7 d after infestation. Reduced rates of selected insecticides were efficacious against fall armyworms on Bollgard II cotton plant tissues and could reduce chemical control costs against field infestations of this pest.
