A new biopesticide from a local Bacillus thuringiensis var. tenebrionis (Xd3) against alder leaf beetle (Coleoptera: Chrysomelidae)

An overview of the production and use of Bacillus thuringiensis toxin

The widespread utilization of traditional chemical pesticides has given rise to numerous negative impacts, leading to a surge in interest in exploring environmentally friendly alternatives. Bacillus thuringiensis (Bt), a bacterium renowned for its insecticidal properties, produces Cry proteins during its lifecycle. These proteins have distinct advantages over traditional chemical pesticides, including higher environmental safety, broader insecticidal spectra, and lower pesticide residues. Consequently, the discovery and application of Bt hold immense significance in plant disease and pest management, as well as in plant protection. Currently, Bt preparations occupy a prominent position as the world's largest and most widely used biopesticides. This article comprehensively reviews the fundamental aspects, insecticidal mechanisms, practical applications, and fermentation technologies related to Bt.

An Overview of Some Biopesticides and Their Importance in Plant Protection for Commercial Acceptance

Biopesticides are natural, biologically occurring compounds that are used to control various agricultural pests infesting plants in forests, gardens, farmlands, etc. There are different types of biopesticides that have been developed from various sources. This paper underscores the utility of biocontrol agents composed of microorganisms including bacteria, cyanobacteria, and microalgae, plant-based compounds, and recently applied RNAi-based technology. These techniques are described and suggestions are made for their application in modern agricultural practices for managing crop yield losses due to pest infestation. Biopesticides have several advantages over their chemical counterparts and are expected to occupy a large share of the market in the coming period.

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

Bacillus thuringiensis (Bt), a natural pathogen of different invertebrates, primarily insects, is widely used as a biological control agent. While Bt-based preparations are claimed to be safe for non-target organisms due to the immense host specificity of the bacterium, the growing evidence witnesses the distant consequences of their application for natural communities. For instance, upon introduction to soil habitats, Bt strains can affect indigenous microorganisms, such as bacteria and fungi, and further establish complex relationships with local plants, ranging from a mostly beneficial demeanor, to pathogenesis-like plant colonization. By exerting a direct effect on target insects, Bt can indirectly affect other organisms in the food chain. Furthermore, they can also exert an off-target activity on various soil and terrestrial invertebrates, and the frequent acquisition of virulence factors unrelated to major insecticidal toxins can extend the Bt host range to vertebrates, including humans. Even in the absence of direct detrimental effects, the exposure to Bt treatment may affect non-target organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability. The immense phenotypic plasticity of Bt strains, coupled with the complexity of ecological relationships they can engage in, indicates that further assessment of future Bt-based pesticides' safety should consider multiple levels of ecosystem organization and extend to a wide variety of their inhabitants.

Possible interference of Bacillus thuringiensis in the survival and behavior of Africanized honey bees (Apis mellifera)

Bacillus thuringiensis (Bt), an entomopathogenic bacterium, has been used as bioinsecticides for insect pest control worldwide. Consequently, the objective of this work was to evaluate the possible effects of commercial formulations of Bt products, Dipel and Xentari, on the survival and behavior of Africanized honey bees (Apis mellifera). Bioassays were performed on foragers and newly emerged (24-h-old) bees that received the products mixed in the food. Their survival and behavior were evaluated through the vertical displacement tests and the walk test, analyzed using software Bee-Move. Then, histological analysis of the mesenterium was performed. As control treatment was used sterile water. The honey bees' survival was evaluated for between 1 and 144 h. No interference of B. thuringiensis, Dipel and Xentari, in the survival of Africanized honey bees were found. Only Xentari interfered with vertical displacement behavior of newly emerged (24-h-old) bees. Both the products tested were selective and safe for A. mellifera.

Bacillus thuringiensis endotoxin production: a systematic review of the past 10 years

Bacillus thuringiensis (Bt) is one of the most promising biological control agents used commercially. Its products can contribute to reducing ecological and environmental problems associated with the use of chemical pesticides. Among the limiting factors of using Bt as bioinsecticide are the costs and ensuring its biological activity, which may vary according to the strain and culture conditions. This systematic review aimed to collect state-of-the-art information on the production of Bt endotoxins and to score the methodological feasibility of the data obtained, thus highlighting possible incoherencies. In order to consolidate recent findings and guide future studies, a total of 47 original articles from the last 10 years was analysed, with special attention being given to corroborating data, identifying inconsistencies and suggesting future adjustments so as to increase data reliability. With a maximum score of 8 points, three production parameters were classified on the following scale: preferable (score: 2), adequate (score: 1) and inadequate (score: 0), and another two parameter were classified as adequate (score: 1) or inadequate (score: 0). No article scored more than 6 out of the maximum of 8, thus reflecting the need for more detailed studies regarding Bt endotoxin production. The lack of standardization of methods and units of measurement also have made a comparison of results and an overall analysis difficult. Standards are suggested in the present study. The inclusion of bioassays and quantifying toxin via alkaline dilution are strongly recommended for studies of this nature, along with LC50 expressed in mg/L. Sixteen articles (34%) did not use either of these suggested methods, which indicates the need for further supporting studies. These findings reinforce the need for robust studies in this area, which could include the development of more affordable and effective bioinsecticides, thus increasing their competitiveness against insecticides derived from unsustainable sources.

Microencapsulation of an indigenous isolate of Bacillus thuringiensis by spray drying

In this study, microencapsulation by spray drying was performed to protect spores and crystals of an indigenous isolate of Bacillus thuringiensis Se13 from environmental stress. The effects of wall material, inlet temperature, and outlet temperature on microencapsulation of Bt-Se13 were investigated using Taguchi's orthogonal array. The most suitable wall material determined as maltodextrin DE10. The optimum inlet and outlet temperatures of spray drier were determined as 160 °C and 70 °C, respectively. The number of viable spores, mean particle size, wetting time, percentage of suspensibility and moisture content of the product produced under optimum conditions were determined as 8.1 × 10¹¹ cfu g^-1, 13.462 µm, 25.22 s, 77.66% and 7.29%, respectively. As a result of efficiency studies on Spodoptera exigua in the laboratory conditions, the LC₅₀ was determined as 1.6 × 10⁴ cfu mL^-1. Microencapsulated Bt-Se13 based bio-pesticide may be registered for the control of S. exigua and can be tested against other lepidopterans which share the same environment.

Biodiversity and pathogenicity of bacteria associated with the gut microbiota of beet armyworm, Spodoptera exigua Hübner (Lepidoptera: Noctuidae)

In order to find an effective and environmentally friendly biocontrol agent against Spodoptera exigua, we isolated and identified a total of 15 different bacterial species belonging to phyla Firmicutes, Proteobacteria and Bacteroidetes. According to the phenotypic, genotypic and phylogenetic properties, bacterial isolates were identified as Bacillus cereus (Se1), Lysinibacillus macroides (Se2), Pseudomonas geniculata (Se3), Paenibacillus tylopili (Se4), Staphylococcus succinus (Se5), Acinetobacter soli (Se6), Chryseobacterium indologenes (Se7), Bacillus toyonensis (Se8), Serratia marcescens (Se9), Paenibacillus amylolyticus (Se10), Paenibacillus xylanexedens (Se11), Enterobacter ludwigii (Se12), Bacillus thuringiensis (Se13), Bacillus thuringiensis (Se14) and Lysinibacillus fusiformis (Se15). Screening of bacterial isolates for insecticidal potential was conducted at 10⁹ cfu ml^-1 bacterial concentration. The highest larvacidal effect was obtained with Bacillus thuringiensis Se13 with 100% mortality. In the dose response experiments performed with this bacterium, the median lethal concentration (LC₅₀) was estimated as 7.5 × 10⁴ cfu ml^-1 against 3rd instar larvae of the pest at 10 days post treatment. The median lethal time (LT₅₀) value of 10⁹ cfu ml^-1 bacterial concentration was also determined as 1.59 days. Phase-contrast and scanning electron microscope studies exhibited that B. thuringiensis Se13 produced different shape and size crystals (bipyramidal, cubic and spherical). Phylogenetic analysis of cry1 and cry2 gene content of this isolate displayed that B. thuringiensis Se13 had 99% homology with cry1Ac and cry2Aa, respectively. Finding from this study indicated that B. thuringiensis Se13 appears to be a promising microbial control agent for use against S. exigua.