Bacillus thuringiensis (Bt) based products have an important role in the management of insecticide resistance, the avoidance of problems induced by the destruction of natural biocontrol, and the reduction of the chemical pesticide load in the environment. An estimated 100 000 ha of early-stage cotton were treated with Bt in 1990, usually in combination with endosulfan or thiodicarb at reduced rates. A further 10 000-20 000 ha of other crops, mainly vines, pome fruits and cole crops, were also treated. Occasional problems have resulted from the limited mode of action and low persistence on crops demonstrated by Bt, and a pricing structure that encouraged its use at marginally effective rates.
