Survival and development of tobacco hornworm larvae on tobacco plants grown under elevated levels of ozone

Tobacco plants, Nicotiana tabacum were grown under different levels of ozone (O-3) in open-top chambers. Ozone concentrations were established by charcoal filtration, which reduced O-3 to approximately one-half ambient, or by the addition of O-3 to unfiltered air to increase concentrations to approximately 1.4 or 1.7 times ambient O-3. Survival of tobacco hornworm, Manduca sexta, larvae was increased when second instars were fed tobacco leaves grown in chambers with elevated levels of O-3. Second instars also gained significantly more weight when they were fed for one week on plants exposed to elevated levels of O-3 than when they were fed plants grown in charcoal-filtered air. Ozone-treated tobacco plants had higher levels of total nitrogen (primarily reduced nitrogen) and soluble carbohydrates (sugars), and lower levels of leaf-surface components, starch, nicotine, and rutin. Increased survival and growth response of hornworm larvae to elevated O-3 levels in these experiments suggests that similar responses could occur in the southeastern US tobacco production areas where O-3 levels can be high enough to injure tobacco plants.