FIELD PERFORMANCE OF COTTONS EXPRESSING TRANSGENIC CRYIA INSECTICIDALPROTEINS FOR RESISTANCE TO HELIOTHIS-VIRESCENS AND HELICOVERPA-ZEA (LEPIDOPTERA, NOCTUIDAE)

Transgenic cotton plants (BTK lines), carrying a gene construction tha t codes for the CryIA(b) or CryIA(c) delta-endotoxins from Bacillus th uringiensis variety kurstaki were evaluated in the field for resistanc e to naturally occurring tobacco budworm, Heliothis virescens (F.), bo llworm, Helicoverpa zea (Boddie), and cabbage looper, Trichoplusia ni (Hubner). Five BTK lines (each line was an independent insertion event ) were evaluated in 1990 and 6 in 1991. Also 2 nontransgenic commercia l cultivars,'Coker 312', the explant source cultivar for the BTK lines , and an adapted cultivar, 'Stoneville 453', were evaluated. A split-p lot design was used with lepidopteran control as the main plot and cot ton lines as the subplots, Main plot treatments were weekly spray appl ications of insecticide for lepidopteran control during 8 or 9 wk of t he growing season, or no insecticidal sprays for lepidopteran control. The season mean numbers of tobacco budworm and bollworm larvae on pla nt mainstem terminals, flower buds and capsels, and the percentage of flower buds and capsels injured were lower for all BTK lines, in spray ed and unsprayed plots, than for the 2 nontransgenic cultivars. Averag ed over both years, the season mean percent injury in plots of the uns prayed Coker 312 was approximate to 23% of the flower buds and 12% of the capsels. In unsprayed plot; of the BTK lines, the season mean perc ent injury was approximate to 2.3 of the flower buds and 1.1 of the ca psels. In unsprayed plots, the number of cabbage looper larvae and the amount of cabbage looper feeding injury to leaves also was lower on t he BTK lines compared with the 2 nontransgenic cultivars. Using the re commended treatment thresholds for tobacco budworm and bollworm of 8-1 5% injured flower buds, none of the BTK lines would have been treated, whereas injury in the 2 non-transgenic cultivars would have required multiple insecticide applications. Averaged over both years, the yield of unsprayed Coker 312 was 1,050 kg/ha and the average of all the uns prayed BTK lines was 1,460 kg/ha. Expression of these cryIA genes in C oker 312 cotton resulted in greater yield, 408 kg/ha, 38.8%, in the pr esence of lepidopteran pests. The use of these insect-resistant BTK li nes or equally efficacious commercial BTK cultivars in production agri culture should reduce insecticide applications for tobacco budworm, bo llworm, and cabbage looper while increasing farm profit and opportunit ies for the use of biological control.