Bt Research 2024, Vol.15, No.5, 232-239 http://microbescipublisher.com/index.php/bt 234 Figure 1 Proposed mode of action of the Vip3 proteins (Adopted from Chakroun et al., 2016) Image caption: The full-length protoxin is proteolytically processed by midgut proteases. The 65-kDa fragment binds to specific receptors (with the 22-kDa fragment still bound or not). Pores are then formed, which leads to the death of the cell (Adopted from Chakroun et al., 2016) 3.3 Synergism between Bt toxins and non-Bt insecticidal proteins Bt toxins also exhibit synergistic interactions with non-Bt insecticidal proteins. For example, the combination of Cry1Ac with cadherin (a non-Bt protein) in insect cell lines has shown a strong synergistic effect on the cytotoxicity of activated Cry1Ac. This suggests that Bt toxin receptors-expressing insect cell lines can be used as an alternative model for evaluating the cytotoxicity of Bt toxins and studying their mechanisms of action. Furthermore, the interaction between Cry1A toxins and the ABC transporter HevABCC2, along with the cadherin protein HevCaLP, in Heliothis virescens demonstrates that both proteins need to be expressed within the same cell for high cytotoxicity, indicating a novel role for HevCaLP in increasing Cry1A toxicity (Bretschneider et al., 2016; Xu, 2024). 4 Applications of Synergistic Combinations in Pest Control 4.1 Bt-based genetically modified (GM) crops with synergistic proteins Bt-based GM crops have been a cornerstone in pest management, particularly in crops like corn, cotton, and soybean. The integration of multiple Bt toxins in these crops has shown significant promise in enhancing pest control efficacy and delaying resistance development. For instance, the combination of Cry1 and Cry2 toxins in Bt cotton has been widely adopted, with substantial success in controlling lepidopteran pests and reducing the reliance on chemical insecticides (Tabashnik, 2015). The inclusion of vegetative insecticidal proteins (Vip3A) alongside Cry proteins has demonstrated synergistic effects, further improving pest mortality rates and providing a broader spectrum of pest control. 4.2 Bt bioinsecticides and synergistic protein formulations Bt bioinsecticides, formulated with multiple Bt toxins, have emerged as a viable alternative to chemical pesticides. Studies have shown that combinations of Cry1, Cry2, and Vip3A proteins exhibit synergistic interactions, significantly enhancing their insecticidal activity against pests like Spodoptera exigua and Spodoptera frugiperda (Baranek et al., 2021). These formulations not only improve pest control efficacy but also help in managing resistance by targeting multiple sites within the pest's physiology. The development of such bioinsecticides is crucial for sustainable pest management, especially in regions where resistance to single-toxin Bt crops has been reported (Jurat-Fuentes et al., 2021; Huang et al., 2023).
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