Biopesticides of bacterial origin represent a substitute for chemical insecticides, but however their use is limited, since most microbes show a narrow spectrum of activity that enables them to kill only certain insect species. Bacillus thuringiensis (Bt) insecticidal crystal proteins (Cry toxins) however offer a number of advantages over synthetic pesticides, including environmental safety, and high specificy to target insects and therefore safety to non-target organisms, like humans and other mammals. Cry toxins have also been introduced into transgenic crops. This approach has resulted in significant reduction in use of chemical insecticides in places where this technology has been embraced. The major weakness of the use of Bt crops is development of insect resistance to Cry toxins developed by mutations. The use of gene stacking of different Cry toxins with different modes of action in the same plant is one strategy to cope with the apperance of insect resistance as well as combining it with the use of refuge strategy. The novel generation of Bt corn express a series of toxins including Cry34Ab1/Cry35Ab1 binary toxin and Cry3Bb toxin. Cry34 proteins, including Cry34Ab1, are the only representatives of crystal toxic proteins that are structurally similar to aegerolysins. Cry35Ab1 forms a complex with an aegerolysin-like Cry34Ab1 protein, and this complex then forms pores in the membrane. Since corn rootworm larvae have already developed resistance to Bt maize, discovery of new protein toxins that do not belong to Bt is very important, so there is less chance of developing cross-resistance.
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