The progress in insect cross-resistance among Bacillus thuringiensis toxins.

Bt crop pyramids produce two or more Bt proteins active to broaden the spectrum of action and to delay the development of resistance in exposed insect populations. The cross-resistance between Bt toxins is a vital restriction factor for Bt crop pyramids, which may reduce the effect of pyramid strategy. In this review, the status of the cross-resistance among more than 20 Bt toxins that are most commonly used against 13 insect pests was analyzed. The potential mechanisms of cross-resistance are discussed. The corresponding measures, including pyramid RNA interference and Bt toxin, "high dose/refuge," and so on are advised to be taken for adopting the pyramided strategy to delay the Bt evolution of resistance and control the target pest insect.