Problems of insect resistance to Bacillus thuringiensis
1994
McGaughey, W.H.
Insect resistance to Bacillus thuringiensis (Bt) has been a recognised problem for only about 6 years. It now seriously threatens both conventional and gene transfer uses for this environmentally safe biological insecticide. Since 1985, the potential for resistance has been demonstrated in at least five insect species, and high levels of resistance among field populations have been reported in one species. In two moth species, Plodia interpunctella and Plutella xylostella, the potential for resistance is widespread among diverse populations and laboratory studies suggest that it can progress to high levels within only a few generations. The mechanism of resistance in these species involves a change in binding affinity of the insects' midgut membrane that is specific for the particular toxin type used in selecting the resistant population. Recognition of the inevitability of Bt resistance in insects has led to increased research on deployment strategies that might delay or prevent its evolution. Although resistance to Bt toxins expressed in genetically engineered plants has not been reported yet, it is imperative that resistance management tactics be developed before resistance reduces the pest control value of Bt. Currently, the focus of strategies for managing resistance is on techniques that minimise selection pressure, such as providing untreated refuges, and on the use of multiple toxins in various mixture, mosaic, rotational, or sequential patterns. Experimental data are needed to support the value of these approaches in different pest and cropping systems.
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