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

Tropospheric ozone (O-3) is an important air pollutant that can injure plan ts, and it may have direct or indirect effects on associated insects. Thus, tobacco plants Nicotiana tabacum L., were exposed to 4 concentrations of O -3 in open-top chambers at the U.S. Department of Agriculture, Agricultural Research Service, Air Quality Research Unit at Raleigh, NC. The O-3 treatm ents were charcoal-filtered ail (CF), nonfiltered air (NF), and NF with O-3 added for 12 h/d (0900-2100 hours EST) to obtain proportions of O-3 approx imate to 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 moth s, Manduca sexta (L.), were counted and removed daily from the plants. Horn worm moths oviposited significantly more eggs on plants grown in the highes t O-3 treatment (NF2). However, when plants were removed from the chambers, or when the O-3 was turned off in the chambers, there were no differences in ovipositional preferences of M. sexta females. Tobacco plants in treatme nts with enhanced O-3 had lower levels of total cuticular cembranoid diterp enes, which are important ovipositional stimulants for M sexta. Therefore, observed changes in leaf-surface chemistry (i.e., lowered cembranoid diterp enes) do not explain the higher oviposition rates by M sexta moths on plant s grown in chambers with enhanced O-3.