Bt Research 2024, Vol.15, No.2, 76-86 http://microbescipublisher.com/index.php/bt 83 8 Applications in Pest Management 8.1 Development of Bt-based biopesticides Bacillus thuringiensis (Bt) has been extensively utilized in the development of biopesticides due to its potent insecticidal properties. Bt-based biopesticides are particularly effective against a wide range of insect pests, including those that affect economically important crops. For instance, Bt toxins have been shown to cause significant mortality in pests such as the diamondback moth, Plutella xylostella, by targeting specific midgut receptors (Guo et al., 2019). Additionally, Bt-based biopesticides have been employed to manage pests like the castor semilooper, Achaea janata, which is a major threat to castor crops (Dhania et al., 2019). The use of Bt biopesticides not only reduces the reliance on chemical insecticides but also minimizes environmental impact and promotes sustainable agricultural practices. 8.2 Transgenic crops expressing Bt toxins Transgenic crops expressing Bt toxins have revolutionized pest management by providing an effective and environmentally friendly alternative to chemical pesticides. These crops, such as Bt corn and Bt cotton, express Cry proteins that are toxic to specific insect pests. For example, transgenic tobacco plants expressing the Cry2Aa2 protein have demonstrated high levels of resistance against both susceptible and Bt-resistant insect strains, including the tobacco budworm and cotton bollworm. Similarly, transgenic potato plants expressing hybrid Bt toxins have shown resistance to pests from different insect orders, such as the Colorado potato beetle and the European corn borer (Naimov et al., 2002). The widespread adoption of Bt crops has significantly reduced crop losses and pesticide usage, contributing to increased agricultural productivity and sustainability. 8.3 Strategies to combat resistance The evolution of resistance in insect pests poses a significant challenge to the long-term efficacy of Bt-based pest management strategies. To address this issue, several approaches have been developed to delay or overcome resistance. One such strategy involves the use of CRISPR/Cas9-mediated genome editing to study and manipulate resistance genes in pests. For instance, knockout strains of the diamondback moth with mutations in the PxABCC2 and PxABCC3 genes have been created to understand the genetic basis of resistance to Cry1Ac toxin (Guo et al., 2019). Another approach is the development of transgenic plants expressing multiple Bt toxins or hybrid toxins with different modes of action, which can reduce the likelihood of resistance development (Naimov et al., 2002). Additionally, understanding the molecular mechanisms of Bt toxin action and resistance, such as the role of ABC transporters and other midgut proteins, can inform the design of novel toxins and resistance management strategies (Heckel, 2012; Pardo-López et al., 2013; Coates et al., 2016). These efforts are crucial for maintaining the effectiveness of Bt-based pest management and ensuring the sustainability of agricultural practices. 9 Concluding Remarks The characterization of plasmid-encoded toxins in Bacillus thuringiensis (Bt) has revealed significant insights into the genetic and functional diversity of these elements. Several studies have identified novel Cry toxins and their unique genetic organizations, such as the orf1-gap-orf2 structure found in the H3 strain, which carries 11 novel Cry proteins on its plasmid pH3-180. The transcriptional analysis of the pBtoxis plasmid in Bt subsp. israelensis has shown that many of its coding sequences are actively transcribed, including those involved in gene regulation and physiological processes. Additionally, the horizontal transfer of toxin-encoding plasmids, such as pTAND672-2, has been demonstrated, highlighting the role of mobile genetic elements in the diversity and adaptability of mosquitocidal bacteria. Furthermore, the construction of recombinant plasmids combining genes from different Bt subspecies has broadened the host range and enhanced the larvicidal activity against various mosquito species. Plasmid-encoded toxins in Bacillus thuringiensis are crucial for the bacterium's insecticidal properties, which are widely utilized in biopesticides. These toxins, particularly the Cry and Cyt proteins, target specific insect larvae, making Bt a valuable tool in integrated pest management. The presence of multiple plasmids carrying diverse
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