Bt Research 2024, Vol.15, No.2, 87-95 http://microbescipublisher.com/index.php/bt 91 5.2 Sub-lethal effects Sub-lethal effects are those that do not cause immediate death but can impair the physiological or behavioral functions of non-target organisms. For example, Bt proteins have been shown to accumulate in spiders, leading to unintended physiological effects (Bordalo et al., 2021). These sub-lethal impacts can manifest as reduced feeding rates, impaired reproduction, or altered development, which can have long-term consequences on population dynamics. In aquatic ecosystems, sub-lethal effects of Bt-based insecticides on shredders and chironomids have been observed, leading to reduced leaf decomposition rates and altered ecosystem functioning (Bordalo et al., 2021). 5.3 Indirect ecological interactions Indirect ecological interactions occur when Bt crops affect non-target organisms through changes in the ecosystem, such as altered prey availability or habitat conditions. For instance, the reduction in target pest populations can lead to a decrease in prey for predators and parasitoids, indirectly affecting their abundance and diversity (Belousova et al., 2021; Bordalo et al., 2021). In some cases, Bt crops have been associated with increased abundance of certain non-target taxa compared to fields treated with conventional insecticides, suggesting that the indirect effects of Bt crops might be less detrimental than those of chemical pest control methods (Marvier et al., 2007; Naranjo, 2009). However, the complexity of these interactions necessitates further research to fully understand the cascading effects within ecosystems (Brunk et al., 2019; Belousova et al., 2021). The mechanisms of non-target effects of Bt crops on invertebrates are multifaceted, involving direct toxicity, sub-lethal impacts, and indirect ecological interactions (Liang et al., 2018; Brühl et al., 2020). While laboratory studies provide valuable insights, field studies are crucial for a comprehensive understanding of these effects in real-world conditions. 6 Mitigation and Management Strategies 6.1 Development of bt varieties with reduced non-target effects The development of Bt crops with minimized impacts on non-target invertebrates is crucial for sustainable agricultural practices. Research has shown that while Bt crops generally have fewer adverse effects on non-target organisms compared to conventional insecticides, there are still some non-target taxa that are affected (Marvier et al., 2007; Wolfenbarger et al., 2008; Naranjo, 2009). To mitigate these effects, it is essential to focus on the strategies, engineering Bt crops to express Cry proteins only in specific tissues or developmental stages can reduce exposure to non-target organisms. For instance, targeting the expression to parts of the plant that are less likely to interact with non-target species can help minimize unintended impacts (Naranjo, 2014; Romeis et al., 2019). Incorporating multiple Bt genes that target different pest species can reduce the overall amount of each toxin produced, potentially lowering the risk to non-target organisms (Duan et al., 2009; Navasero et al., 2016). Developing new Bt proteins that are highly specific to target pests while being harmless to non-target species can further reduce ecological risks. Studies have shown that different Cry proteins have varying effects on non-target organisms, suggesting that careful selection and design of these proteins are vital (Naranjo, 2014; Krogh et al., 2020). 6.2 Use of buffer zones and refuges Buffer zones and refuges are critical components in the management of Bt crops to protect non-target invertebrates and delay resistance development in target pests. These strategies involve the planting non-Bt crops adjacent to Bt fields can provide a habitat for non-target organisms and help maintain their populations. This approach also supports the survival of susceptible pest individuals, which can mate with resistant ones, thereby slowing the development of resistance (Naranjo, 2009; Navasero et al., 2016). Buffer zones of non-Bt vegetation around Bt fields can act as a barrier, reducing the movement of Bt toxins into surrounding ecosystems. These zones can also serve as habitats for beneficial non-target species, promoting biodiversity and ecological balance (Wolfenbarger et al., 2008; Naranjo, 2014). Rotating Bt and non-Bt crops spatially and temporally can reduce the continuous exposure of non-target organisms to Bt toxins, allowing their populations to recover and maintain ecological functions (Marvier et al., 2007; Duan et al., 2009).
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