Zixuan Wang

Bacillus thuringiensis (Bt) is one of the most extensively used microbial insecticides, attributed to the action of insecticidal crystal proteins (ICPs), primarily Cry toxins, which mediate damage to the insect midgut epithelium. Recent evidence suggests that Bt toxicity is also strongly influenced by its physiological state and interactions with the host gut environment. Biofilm formation represents an important adaptive strategy that enhances bacterial stress tolerance and may modulate insecticidal performance, although the underlying mechanisms remain unclear. However, it is still unclear how Bt in the biofilm state alters host responses at the structural and transcriptomic levels. Using the tea plantation pest Ectropis grisescens as a model, we systematically evaluated the insecticidal efficacy of biofilm-state Bt formulations and their synergistic effects with a biofilm inducer system composed of Tween-80, tea saponin, matrine, and tea polyphenols. Bioassays showed that the biofilm-state Bt supplemented with composite inducers achieved the highest corrected mortality and reduced the LC₅₀ against neonate larvae by 2.88-fold compared with conventional planktonic Bt. Histopathological, biochemical, and transcriptomic analyses further revealed that biofilm-state Bt caused more severe midgut damage and induced extensive remodeling of detoxification- and stress-response-related pathways. These findings highlight Bt physiological state as a critical determinant of formulation efficacy and provide a novel framework for Bt optimization through microbial physiological regulation.

Phyllotreta striolata is a major pest of Brassica chinensis, with chemical pesticides being the primary method for pest control. However, their negative impact on crop growth and environmental risks have prompted the search for low-toxicity, environmentally friendly alternatives. This study systematically evaluates the control effectiveness of two commonly used chemical pesticides, Zu Jia^® and Jie Tiao^®, along with their impact on the growth characteristics of B. chinensis and compares them to the biopesticide Bacillus thuringiensis (Bt) strain G033A. The control efficacy was assessed by measuring the insect population reduction rate and plant physiological indicators (weight, plant height, chlorophyll content, and root length). The differences between biopesticide and the two chemical pesticide treatments were analyzed. The results indicated that both Bt strain G033A and the chemical pesticides significantly controlled P. striolata. However, chemical pesticides (Zu Jia^® and Jie Tiao^®) significantly reduced the chlorophyll content, plant height, and weight of B. chinensis (p < 0.05), whereas Bt strain G033A had no significant adverse effects on these plant traits (p > 0.05). The colonization characteristics of the Bt strain suggest potential for sustained pest control, while chemical pesticides exhibited rapid pest suppression effects. The findings highlight a novel IPM strategy that integrates the long-lasting efficacy of Bt biopesticides with the rapid action of chemical pesticides, offering a more sustainable and balanced approach to P. striolata management in B. chinensis cultivation.

This study investigated the effects of fertilizers on the biofilm formation, ultraviolet (UV) resistance, and insecticidal activity of Bacillus thuringiensis (Bt). Bacillus thuringiensis, a widely used microbial pesticide, has a minimal environmental impact and is highly effective against specific pests but is susceptible to environmental factors in field applications. Bacterial biofilms provide protection for Bt, enhancing its survival and functionality in the environment. However, the mechanisms by which fertilizers regulate the characteristics of microbial pesticides and enhance biofilm formation are not well understood. This study evaluated the effects of six fertilizers on the bacterial biofilm formation, the UV resistance, and the insecticidal activities of Bt wettable powders. The results demonstrated that fertilizers significantly enhanced the performance of three Bt preparations (Lv’an, Kang’xin, and Lu’kang). A compound fertilizer with 8.346 g/L of KCl, 2.751 g/L of ZnSO₄·7H₂O, and 25.681 μL/mL of humic acid was identified by response surface optimization, achieving the maximum BBF formation with OD₅₉₅ value of 2.738. Furthermore, KH₂PO₄, HA, and ZnSO₄·7H₂O notably improved the survivability of Bt preparations under prolonged UV exposure, with the compound fertilizer providing the greatest protection. What’s more, fertilizers reduced the LC₅₀ values of all Bt preparations, with the compound fertilizer decreasing the LC₅₀ of the Lv’an Bt wettable powder to 0.139 g/L, a 3.12-fold increase in efficacy. This study demonstrated that fertilizers significantly enhance the UV resistance and insecticidal activity of Bt wettable powders by promoting bacterial biofilm formation. Herein, this study provides new strategies and theoretical support for Bt applications in modern sustainable agriculture.