Observations on Feeding and Movement of Tobacco Hornworm Larvae12

Eighteen mature potted tobacco plants were set up in isolated rows under constant light in an experimental room held at a mean temperature of 25.6°C and 75% relative humidity. Eggs of the tobacco hornworm moth, Manduca sexta (Johannson), were placed on leaves of 6 plants which were designated P-5, P-10, P-15, P-30, P-60, and P-90, according to the number of eggs placed on the plants. Intraplant movement did not occur until larvae had completed all of the 3rd and part of the 4th instars and had consumed most, if not all, of the leaf where the eggs had been placed. Interplant movement became evident as the plants were denuded and was most evident on plants P-30 P-60, and P-90. Larvae on P-10 and P-15 did not appear to be any more crowded than those on P-5, which was used as the control. The study demonstrated that movement of tobacco hornworm larvae between plants does occur but only under abnormally crowded conditions.