Ovipositional response of tobacco hornworm moths (Lepidoptera: Sphingidae) to tobacco plants grown under elevated levels of ozone

Abstract

Tropospheric ozone (O3) is an important air pollutant that can injure plants, and it may have direct or indirect effects on associated insects. Thus, tobacco plants, Nicotiana tabacum L., were exposed to 4 concentrations of O3 in open-top chambers at the U. S. Department of Agriculture, Agricultural Research Service, Air Quality Research Unit at Raleigh, NC. The O3 treatments were charcoal-filtered air (CF), nonfiltered air (NF), and NF with O3 added for 12 h/d (0900-2100 hours EST) to obtain proportions of O3 ≃1.4 times ambient (NF1) and 1.7 times ambient (NF2). After plants had been exposed to ozone for at least 5 d, eggs from tobacco hornworm moths, Manduca sexta (L.), were counted and removed daily from the plants. Hornworm moths oviposited significantly more eggs on plants grown in the highest O3 treatment (NF2). However, when plants were removed from the chambers, or when the O3 was turned off in the chambers, there were no differences in ovipositional preferences of M. sexta females. Tobacco plants in treatments with enhanced O3 had lower levels of total cuticular cembranoid diterpenes, which are important ovipositional stimulants for M. sexta. Therefore, observed changes in leaf-surface chemistry (i.e., lowered cembranoid diterpenes) do not explain the higher oviposition rates by M. sexta moths on plants grown in chambers with enhanced O3.