Bt Research 2024, Vol.15, No.5, 223-231 http://microbescipublisher.com/index.php/bt 224 target the midgut cells of mosquito larvae. The Cry toxins, such as Cry4Aa, Cry4Ba, and Cry11Aa, bind to specific receptors in the midgut, causing cell lysis and larval death. Cyt1Aa, another crucial toxin, acts synergistically with Cry toxins by inserting itself into the cell membrane, enhancing the overall insecticidal effect and reducing the risk of resistance development (Hayakawa et al., 2017; Silva-Filha et al., 2021). 2.2 Key Bt strains used in mosquito control The primary Bt strain used in mosquito control is Bacillus thuringiensis var. israelensis (Bti). Bti is favored due to its high specificity and effectiveness against mosquito larvae, including species such as Aedes aegypti and Culex pipiens. Other strains like Bacillus sphaericus are also used, known for their persistence in field conditions. Recent advancements have seen the development of formulations combining Bti with other bacterial strains or secondary metabolites to enhance efficacy and reduce resistance (Park et al., 2016; Derua et al., 2018). 2.3 Historical development and global implementation of bt-based mosquito control programs The use of Bt-based mosquito control programs began in the late 20th century, with Bti being introduced as a microbial larvicide. Over the years, Bti has been widely adopted globally due to its environmental safety and effectiveness. Programs have been implemented in various regions, including the highlands of western Kenya, where long-lasting formulations like FourStar® and LL3 have been used to control malaria vectors without significantly impacting non-target organisms. Additionally, Bt-based control methods have been integrated into broader public health strategies to combat mosquito-borne diseases, demonstrating significant reductions in mosquito populations and disease transmission (Allgeier et al., 2019). 3 Efficacy of Bt-Based Control Programs in Reducing Mosquito Populations 3.1 Field trials and case studies in urban and rural areas 3.1.1 Successes in dengue and malaria control programs Bt-based mosquito control programs have shown significant success in various field trials and case studies. A community-based application of Bacillus thuringiensis var. israelensis (Bti) in Rwanda demonstrated a substantial reduction in Anopheles larval habitats, with a 49% reduction in supervised areas and a 28% reduction in community-led areas. This intervention also nearly eliminated pupal production, thereby preventing the emergence of adult mosquitoes (Hakizimana et al., 2022). Similarly, a large-scale field trial in Burkina Faso using Bti for biological larviciding achieved a 77.4% reduction in adult Anopheles mosquito abundance, indicating the potential of Bt-based methods in malaria vector control (Dambach et al., 2020). 3.1.2 Variability in efficacy based on environmental conditions The efficacy of Bt-based mosquito control programs can vary significantly based on environmental conditions. Factors such as seasonality, local climate, and the specific ecological characteristics of the intervention area can influence outcomes. For example, the effectiveness of biological methods like Wolbachia-infected mosquitoes can be hampered by extreme weather conditions such as heatwaves, which may result in the loss of Wolbachia infection (Ogunlade et al., 2023). Additionally, the success of community-based interventions may depend on the level of community engagement and the availability of resources for sustained implementation (Figure 1) (Salazar et al., 2019). 3.2 Comparative effectiveness: Bt-based vs. chemical-based mosquito control When comparing Bt-based mosquito control methods to chemical-based approaches, several studies highlight the advantages of biological methods. Chemical methods, while initially effective, often lead to increased resistance in mosquito populations, reducing long-term efficacy (Ogunlade et al., 2023). In contrast, Bt-based methods, such as the use of Bti, have shown sustained effectiveness without the risk of resistance development. A systematic review and meta-analysis found that environmental methods, including the use of Bti, were more sustainable and posed fewer risks of environmental contamination compared to chemical insecticides (Buhler et al., 2019). Moreover, the use of Wolbachia-infected mosquitoes has demonstrated a significant reduction in dengue incidence, with a protective efficacy of 77.1% in treated areas (Utarini et al., 2021).
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