Insect Resistance to Bt

In 1985, McGaughey [37] reported that Plodia interpunctdla became resistant to Bt when reared for several generahons in the laboratory with a sublethal dose of a Bt commercial product, presumably Bt kurstaki HDl. When Van Rie et al. 

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Insects have evolved resistance to Bt toxins in the laboratory, yet only one crop pest, the diamondback moth (Plutella xylostella), has evolved resistance to Bt toxins under open field conditions (Tabashnik et al. 2003). But this resistance was not caused by Bt crops, rather it occurred in response to repeated foliar sprays of Bt toxins to control this pest on conventional (non-GE) vegetable crops (Tabashnik 1994). Based partly on the experience with diamondback moth and because Bt crops cause season-long exposure of target insects to Bt toxins, some scientists predicted that pest resistance to Bt crops would occur in a few years. 

Tabashnik, B. E., Yves Carriere, TimothyJ. Dennehy, Shai Morin, Marks. Sisterson, Richard T. Roush, Anthony M. Shelton, and Jian-Zhou Zhao. Insect resistance to transgenic Bt crops Lessons from the laboratory and field. Journal of Economic Entomology 96 1031. 

Reduced binding of toxin is a primary mechanism of insect resistance to Cry proteins (Ferre and Van Rie, 2002). Resistance of the Indian meal moth to Bt was due to a 50-fold reduction in affinity of the membrane receptor (from brush borer membrane vesicles of larval midguts) for 5-endotoxin. In pinkbollworms, Bt resistance is associated with reduced binding of CrylAb to the brush borer membrane vesicle. Similarly, CrylAc resistance in diamondback moths was demonstrated to be due to dramatically reduced target binding. 

In this paper, the use of Bt -based insecticides as tools for controlling insects resistant to synthetic insecticides will be explored through a review of the development of two very different Bt based products M-One Insecticide, based on the naturally occurring Bt variety son diego controls the Colorado potato beetle, a pest that has... 

Two problems must be considered. Insects do develop resistance to the Bt toxin.m This problem... 

More recently, Mota-Sanchez et al. (2002) found a similar trend using database analysis. Table 10.3 shows that the majority of reported cases of resistance are arthropod resistance to organophosphate (44%) and organochlorine (32%) insecticides. It is understandable, because these two classes of insecticides have been used in pest control for over half a century. As shown in Table 10.4, twelve species of insects have developed resistance to various strains of Bt and Bt toxins in the laboratory and/or the field. 

According to Gianessi et al. [7], insect resistant Bt cotton has been introduced in many... 

Although it was once thought that insects would not develop resistance to microbial insecticides, scientists have confirmed cases of diamondback moths in commercial farms that showed resistance. This is another argument for using BT with care, and only after trying cultural or physical control methods for which resistance is not a factor. 

By incorporating these characteristics of the Bt toxin into valued crop species, crop resistance to insects feeding on crop species may be enhanced helping to increase vitality, size, and acreage yields. 

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