Abstract
Bacillus thuringiensis (Bt) is currently the most successful microbial biopesticide globally. Despite this, its potential to mitigate the devastating effects of chemical pesticides and its widespread adoption in large-scale field applications have not yet been fully realized due to its sensitivity to various environmental stressors. Among these stressors are ultraviolet radiation, temperature, precipitation, pH fluctuations, soil properties, and leaf surface morphology. Previous studies have assessed the individual impact of these factors on the degradation of Bt spores and Cry proteins. This review provides critical insight into the major environmental stressors that influence the persistence, stability, and efficacy of Bt-based biopesticides in field applications. Particularly, we address the mechanisms by which these stressors degrade Bt biopesticides and contribute to their poor success in field applications. Moreover, various formulation strategies, including microencapsulation, nanotechnology and Pickering emulsions, drying, hydrogels, and cell-encapsulation, that have been adopted over the past decades to overcome the environmental challenges associated with Bt-based pesticides are discussed. The strengths and limitations of these techniques in improving the stability and persistence of Bt biopesticides are evaluated. This study serves as a guide for researchers, farmers, engineers, and Bt biopesticide manufacturers regarding the use of formulation strategies to improve the environmental shelf-life, stability, and efficacy of Bt products.
Introduction
Bacillus thuringiensis (Bt) is a Gram-positive, aerobic, and endospore-forming bacterium widely distributed across various ecosystems, including soil, water, plant surfaces, dead insects, and grain storage facilities (Argôlo-Filho and Loguercio, 2013; Karim et al., 2023; Yılmaz et al., 2025). The most distinctive feature distinguishing this bacterium from its closest relatives such as Bacillus cereus is its ability to produce toxic, proteinaceous, parasporal crystalline inclusions, known as δ-endotoxins, during the sporulation phase (Yilmaz et al., 2017). These endotoxins exhibit highly specific biological activity against target insect pests and certain invertebrates (Ibrahim et al., 2010). Currently, there are over 1000 pesticidal homologs of Bt toxins classified under the Cry, Cyt, App, Mcf, Mpf, Mpp, Mtx, and Vip groups (BPPRC, 2026).
Today, Bt is recognized as the most reliable, sustainable, and eco-friendly alternative to the devastating effects of synthetic chemical pesticides on the environment and human health. Bt-based products account for approximately 97% of the global microbial biopesticide market (Ramírez-Guzmán et al., 2026), and are projected to reach a market value of USD 16.88 billion by 2031 (Ghodake et al., 2026).
Despite the success and potential of Bt usage, the global adoption of Bt-based products in agriculture and forestry faces significant practical hurdles, largely due to their low stability and limited persistence under field conditions (De Haddad et al., 2005). Although highly effective under laboratory conditions, Bt biological agents degrade rapidly when applied in the field due to abiotic stress factors, thereby diminishing their pesticidal efficacy. The total field persistence of Bt, which is defined as the duration during which pathogenicity remains active in the field, is significantly influenced by climatic and environmental parameters such as ultraviolet radiation, precipitation, extreme temperature fluctuations, and pH (Zhu et al., 2022). This is primarily due to the direct exposure of Bt spores and Cry proteins to these environmental factors following field application. The structural incompatibility that often exists between Bt and open field conditions constitutes the major obstacle to the mass adoption and widespread use of these products. Naghavi et al. (2016) reported that the efficacy of unprotected Bt formulations, especially those exposed to direct sunlight, can be completely lost within as little as 10 days. In extreme cases, losses of up to 95–99% have been recorded within the first three days following field application (Melo et al., 2025). This rapid degradation necessitates much more frequent field applications to keep pest populations below the economic injury level. However, increased application frequency raises costs and reduces the competitiveness of Bt-based biopesticides against synthetic chemical pesticides.
In response to overcoming the barriers of poor field stability and short-term persistence of Bt-based biopesticides, researchers have explored numerous formulation techniques designed to protect Bt from harmful environmental factors. These techniques aim to extend the shelf life of Cry toxins and prevent their rapid degradation in the environment. In this context, formulation strategies designed to enhance the field efficacy of Bt biopesticides typically rely on biodegradable biopolymers, additives, and suitable carriers (Kumar et al., 2019).
Adopting effective and appropriate formulation techniques requires a thorough understanding of the key factors and mechanisms responsible for the rapid decline in efficacy and the degradation of Bt-based biopesticides. While previous studies have discussed the environmental persistence of Bt and various formulation strategies (Brar et al., 2006; De Oliveira et al., 2021; Kumar et al., 2019), this review expands upon that body of work by comprehensively discussing the environmental factors affecting Bt and their impact on the persistence and efficacy of Bt-based biopesticides under field conditions. Furthermore, the review covers both historical approaches and current developments in formulation techniques, placing special emphasis on cutting-edge strategies such as sulfur quantum dots, cell encapsulation using bacterial ghosts, biopolymer hydrogels, and fluidized-bed drying. Additional significant formulation strategies employed to mitigate the adverse effects of abiotic stress factors on the stability and persistence of Bt are also discussed.
Section snippets
Effects of environmental stressors on Bt stability
The success of Bt-based biopesticides in agricultural and forestry applications largely depends on the persistence and stability of the active components (spores and insecticidal crystal) in the application area. Formulations that demonstrate high toxicity under laboratory conditions can be rapidly inactivated by the cumulative effect of abiotic stress factors when applied to field conditions. The major abiotic factors determining the environmental fate of Bt include sunlight, precipitation
The fate of Bt in the soil ecosystem
Soil is not only a natural habitat of Bt but also serves as a reservoir where Bt spores and pesticidal proteins such as Cry, Cyt, and Vip toxins accumulate following agricultural management and forestry practices. While Bt and its insecticidal components may naturally occur in soil microflora at low levels, they are introduced in large quantities through the application of synthetic biopesticides (Helassa et al., 2011). Bt agents enter the soil environment via three primary pathways: (1) direct
Advancements in formulation strategies to enhance the environmental stability of Bt biopesticides
The inherent vulnerability of Bt-based biopesticides to environmental stressors such as UV radiation, thermal fluctuations, wash off, and enzymatic biodegradation has necessitated the use of advanced formulation techniques. These techniques aim to enhance efficacy under field conditions and extend shelf and field life, thereby enabling Bt biopesticides to compete with synthetic chemical pesticides. Since the application of pure spore-crystal suspensions alone to agricultural, forestry, or
Conclusion and future prospects
The environmental fate of Bt relies on a dynamic balance between the structural integrity, often compromised by abiotic stressors, the survival strategies of the bacterium, and the protection provided by advanced formulation strategies. Over the years, extensive research has led to the development of advanced formulation techniques designed to shield Bt biopesticide from harmful environmental factors while enhancing their bioavailability. Notable among these advanced formulations are SDQs, cell
CRediT authorship contribution statement
Abdul Aziz Karim: Writing – review & editing, Writing – original draft, Visualization, Software, Methodology, Investigation, Conceptualization. Abdul Razak Ahmed: Writing – review & editing, Writing – original draft, Conceptualization. Semih Yilmaz: Writing – review & editing, Writing – original draft, Visualization, Supervision, Methodology, Investigation, Conceptualization.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
