Survival and Growth of Bollworm and Tobacco Budworm on Nontransgenic and Transgenic Cotton Expressing a CryIA Insecticidal Protein (Lepidoptera: Noctuidae)
Larval and pupal survival and development were assessed for bollworm, Helicoverpa zea (Boddie), and tobacco budworm, Heliothis virescens (F.), fed the transgenic variety (BTK) of cotton, Gossypium hirsutum L., that expressed an insecticidal protein, CryIA(c) from Bacillus thuringiensis Berliner subsp. kurstaki . The parameters measured for bollworm and tobacco budworm fed flower buds excised from BTK or nontransgenic (non-BTK) cotton plants were percentage of survival, length of immature stage, length of pupal stage, larval/ pupal weights, and sex ratio of each instar. Bollworm and tobacco budworm provided with BTK flower buds as 1st, 2nd, 3rd, and 4th instars, fed little and died after a period of ≍1–4 d. Importantly, a large percentage of 5th instars of both species survived, pupated, and became adults on the BTK flower buds. Significantly more bollworm 5th instars pupated and survived to the adult stage when fed non-BTK cotton (76.0 and 51.3%, respectively) compared with those fed BTK cotton (46.0 and 27.1 %, respectively). However, the number of tobacco budworm 5th instars that pupated and emerged as moths when fed non-BTK flower buds (73.3 and 41.3%, respectively) was not different from those fed BTK flower buds (75.3 and 48.0%, respectively). Larval weight was significantly lower for bollworm but not for tobacco budworm fed BTK flower buds as 5th instars. Total length of bollworm and tobacco budworm larval life was greater for the larvae fed non-BTK flower buds compared with the larvae fed BTK flower buds during the 1st–4th instars. Pupal weight, length of pupal stage, and the percentage of male and female pupae produced were not significantly different between the 2 plant phenotypes for the 2 insect species. These results suggest that these transformed BTK cotton plants are highly toxic to 1st–4th instars of bollworm and tobacco budworm, but not to 5th instars. Movement of 5th instars of either insect species from non-BTK plants to BTK cotton plants in mixed stands could result in feeding and injury to BTK plants.