ABSTRACT
The importance of Bt in an environmentally sound insect control program is well accepted. Therefore there is an active interest in search for novel toxins as well as in the discovery of more active strains. The bacterial strains used for all of the early and some of the current Bt foliar insecticides are wild type strains, that is, they were found in nature in the form in which they are used to produce the microbial spray. The use of conventional Bt insecticides, however has limitation like narrow specificity, low potency and short shelf life. On the other hand, certain combinations of Cry proteins have been shown to exhibit synergistic effects. Therefore, genetic manipulation of Bt - to create combinations of genes more useful for a given application than those known to occur in natural isolates - may be desirable. These combinations can be constructed by various approaches that utilize the tools of molecular biology and genetic engineering, as well as conventional microbiological methods.
