Feeding behavior of bollworm and tobacco budworm (Lepidoptera : Noctuidae)larvae in mixed stands of nontransgenic and transgenic cotton expressing an insecticidal protein

Feeding behavior of third-instar bollworm, Helicoverpa ten (Boddie), and to bacco budworm, Heliothis virescens (F.), was observed in pure and mixed sta nds of nontransgenic and transgenic cotton (BTK), Gossypium hirsutum L., ex pressing an insecticidal protein CryIA(c) from a bacterium, Bacillus thurin giensis Berliner subsp. kurstaki. Five plant stands composed of BTK and non -BTK plants were evaluated; two pure stands and three mixed stands. Percent age ratios of BTK to non-BTK plants in the stands were 100:0, 75:25, 50:50, 25:75 and 0:100, respectively. In all stands with BTK plants, fewer bollwo rm and tobacco budworm larvae were found on BTK plants than non-BTK plants 24 h after infestation with third instars. At 48 h, significantly fewer tob acco budworm larvae, but not fewer bollworm larvae, were found on BTK plant s. However, the number of larvae of either insect did not increase on non-B TK plants compared with the initial infestation density of three larvae per plant. The number of obacco budworm injured flower buds, and capsules was lower in all plant stands containing BTK plants compared with the pure stan d of non-BTK at 48 h after infestation. Higher numbers of larvae on non-BTK plants were possibly the result of larval intoxication, reduced feeding, a nd increased plant abandonment and death on BTK plants rather than a classi cal feeding preference. Unexpectedly, the number of newer buds and capsules injured ly bollworm and tobacco budworm when averaged per plant for all pl ants in a stand, differed little among the 75:25, 50:50 and 25:75 plant mix tures. These data suggest that larvae of both species frequently moved amon g plants, feeding indiscriminately on BTK and non-BTK plants.