Toxicity of Nicotine in Synthetic Diets to Larvae of the Tobacco Hornworm1, 2

First, 3rd, and 5th instars of the tobacco hornworm, Manduca sexta (L.) (Lepidoptera: Sphingidae), were affected adversely in survival, rate of development, and weight of their prepupae or pupae by 2% or higher concentrations of nicotine incorporated in a synthetic diet. One percent nicotine in the diet had no observable effect, while 1.5% nicotine had a slight effect on survival and rate of development of 1st and 3rd instars. Under free choice conditions, hornworm larvae fed more on diets without nicotine than on diets containing nicotine, especially on those diets with high nicotine concentrations. Although tobacco hornworm larvae may be adapted to feeding on nicotine-containing plants, resistance to this insect in solanaceous plants could result from the presence of nicotine and/or related alkaloids in the plant.