These crops contain genes from bacteria that make them toxic to some insect pests. A central concern in regulating these genetically modified crops is the risk of insects evolving resistance to the Bt toxins.
To reduce this risk, the "high dose/refuge" strategy is now being used, in which non-Bt fields (refuges for insect pests) are planted near Bt fields (where there is high dose of toxin).
In the November issue of Ecology Letters, Ives and Andow use mathematical theory to explain how the high dose/refuge strategy works. This analysis leads to several unexpected results. For example, for some Bt crops and some pests, spraying insecticides in refuges should not severely compromise the value of refuges.
This makes the high dose/refuge strategy more practical by allowing farmers to protect their crops in refuges. The new theory could lead to new resistance management strategies.