Bt Resistance Management: Have We Been Lucky or Smart?

Prior to the development of plants genetically engineered to express insecticidal crystal proteins (ICP) from Bacillus thuringiensis (Bt), Bt had been a relatively minor insecticide, with total sales <2% in the annual $8 billion global market. However by 2004, 22.5 million hectares of Bt crops (maize and cotton) were grown worldwide, making Bt one of the most widely used insecticides. Bt plants were first commercialized in 1996 amid concern from some scientists, regulators and environmentalists that the widespread use of Bt crops would inevitably lead to resistance and the loss of a highly valued, safe insecticide. Ten years later, there has been no evidence of any insect species having developed resistance to Bt plants. The absence of resistance to Bt plants is remarkable and greatly exceeds the typical period of time before resistance first occurs to most conventional insecticides. However, caution is warranted since the ability of some species of agriculturally important insects to develop resistance to an ICP has been documented in the field with the diamondback moth and in the greenhouse with the cabbage looper.