Bt-Resistance Update

Good news for cotton growers: Two of their biggest pests, cotton bollworm and tobacco budworm, have not become more resistant to the natural insecticide Bacillus thuringiensis (Bt), according to Agricultural Research Service scientists.

That finding comes from an ongoing ARS project to develop a reliable system for tracking insect resistance to Bt. In 1996-97, the ARS researchers studied 67 insect colonies (24 tobacco budworm and 43 cotton bollworm) in nine states.

Monsanto first developed crops with built-in Bt in the early 1990s as an alternative to synthetic insecticides. Today, Bt-formulated crops are a major source of insect control. Many crops, including corn, cotton and potatoes, have been genetically engineered with the Bt gene to provide "homegrown" protection against pests. Cotton with built-in Bt is grown throughout the United States and in Australia.

Over time, some insects can develop resistance to insecticides, which means more chemicals must be applied to achieve control. This can lead to environmental hazards as well as increased costs for the grower. Several pests, including the indianmeal moth, the diamondback moth and at least nine other insects, have developed resistance to Bt.

ARS researchers plan to establish Bt.-resistance thresholds that would trigger remedial action. They're also working to determine the appropriate actions to take if resistance is discovered.

Scientific contact: Dick D. Hardee, Southern Insect Management Research Unit, Stoneville, Miss., phone (601) 686-5231, fax (601) 686-5421, dhardee@ag.gov.