The Use of Disabled Insecticidal Proteins (DIPs) to Investigate the Interaction Between Aedes aegypti-Active Toxins from Bacillus thuringiensis

A variety of pesticidal proteins derived from the bacterium <i>Bacillus thuringiensis</i> exhibit activity against the yellow fever mosquito <i>Aedes aegypti</i> and are used to control this insect vector. Several of these proteins, including Cry1Ca and Cry2Aa, additionally have activity against lepidopteran insects. Furthermore, the specificity of Cry2Aa has recently been shown to depend on domain I of the Cry protein, whereas it is generally recognized that domain II is the primary specificity-determining domain. This work has made use of disabled forms of three Cry proteins (Cry2Aa, Cry1Ca and Cry11Aa) and one naturally non-active protein (Cry2Ab) in an in vivo competition assay to investigate whether Cry2Aa and the dual-active Cry1Ca share a common receptor with the other pesticidal proteins. It was found that despite their differing specificities and potential modes of action, all of the <i>Aedes</i>-active proteins tested made use of a common receptor, although evidence is presented that Cry2Aa can use multiple receptors. When additional toxins (Cry41Aa, Cry1Aa, Cry1Ac) with no activity against this mosquito were tested, they too were found to share the same receptor, suggesting that Cry toxins may have evolved to utilize a common set of receptors in insects but that additional factors determine species specificity.