BEHAVIOR, GROWTH, SURVIVAL, AND PLANT INJURY BY HELIOTHIS-VIRESCENS (F) (LEPIDOPTERA, NOCTUIDAE) ON TRANSGENIC BT COTTONS

Six cotton lines were evaluated for resistance to tobacco budworm, Heliothis virescens (F.), in two glasshouse experiments. The cotton lines were four transgenic somaclones carrying the delta-endotoxin gene (Bt) from Bacillus thuringiensis variety kurstaki and a marker gene (NPTII), and two control lines without the Bt gene (one transgenic control carrying only the NPTII gene, an antibiotic resistance marker gene, and one nontransgenic control). In a behavior experiment, the lines were evaluated for their influence on feeding, resting, locomotion, and spin-down (i.e., leaving the plant on a silken thread) behaviors of third-instar H. virescens. The percentage of time larvae were observed in spin-down behavior was significantly greater on one somaclone carrying the Bt gene than for the nontransgenic 'Coker 312' control. No significant differences were observed in percentage of time larvae spent feeding or resting, or in the occurrence of larvae on flower bud, leaf, or stem-petiole on the six lines. However, more larvae were found in the terminals of one somaclone carrying the Bt/NPTII genes than for the 'Coker 312' control. In a second experiment, neonates were confined on the six cotton lines for 10 d to compare larval growth, survival, and plant injury. Larval weight (fresh) and injury to small bolls were reduced on one somaclone carrying the Bt gene compared with the nontransgenic control. However, flower bud injury was not different among the six lines. These data suggest that the transgenic Bt lines were not expressing the delta-endotoxin at levels sufficient to have a relatively large influence on larval behavior, growth, survival, or plant damage.