Cry1Ac Toxic Protein in Overwintered Volunteer and Annual Seeded NUCOTN 33B7 (Bt) and Deltapine (DPL) 5415 Cottons: Efffects on Pink Bollworm (PBW) and Tobacco Budworm (TBW) Larval Mortalities

Abstract

Season-long protection from pink bollworm (PBW), Pectinophora gossypiella (Saunders), damage has been outstanding each year, since 1996, in NuCOTN 33B7 (Bt) commercial cotton plantings in Arizona. Cotton is a perennial plant and whether or not the insect toxic protein was expressed in overwintered Bt cotton was unknown. This could be a consideration in Arizona Bt resistance monitoring in the field since occasional overwintered volunteer cotton plants may occur. In 2002 we studied Cry1Ac levels in overwintered volunteer Bt cotton plants and determined their effects on PBW and tobacco budworm (TBW), Heliothis virescens F., larval mortalities. No TBW larvae survived three-day feeding periods on Bt leaves compared with < 3% TBW larval mortality feeding on DPL 5415 leaves. PBW larval mortality after three-day feeding on flower buds or seven-day feeding on Bt cotton bolls exceeded 98% compared with 40 to 41 % mortality feeding in DPL 5415 fruiting forms. Cry1Ac toxic protein in leaves, flower buds or cotton bolls of overwintered Bt cotton was not significantly different compared with 2002 seeded cotton.