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

Beauveria bassiana associated with a novel biomimetic hydrogel to control Aedes albopictus through lure and kill ovitraps

BACKGROUND

Within the framework of sustainable and effective control methods for Aedes albopictus, two different conidial suspensions, BbCS-1 and BbCS-2 (respectively without and with nutrients), were used as solvents for the biopolymers water-soluble 2-hydroxyethylcellulose (HEC) and sodium alginate (SA). In this way, two different classes of hydrogels were prepared for each polymer (previously shown to attract tiger mosquito oviposition) to produce HEC-based and SA-based Bb/Gel systems with and without nutrients. The aim was to achieve a long-lasting and cost-effective lure-and-kill oviposition substrate useful for lethal ovitraps. Beauveria bassiana (Bb) survival and growth in the different Bb/Gel systems were monitored for 24 days. Following the growth assay, 24-day-old Bb/Gel systems were tested against Ae. albopictus eggs through a hatching test to evaluate their lethal effect.

RESULTS

Gel systems enhance Bb's longevity (up to 24 days) more effectively than standard liquid conidial suspensions, proving that tested HEC- and SA-based hydrogels are not toxic for Bb (biocompatibility) and create a microenvironment suitable to sustain prolonged fungal growth. In particular, the results indicate that gel system based on hydroxyethylcellulose is a suitable delivery substrate for supporting the activity of Bb and is simultaneously effective against Ae. albopictus eggs through a combined mechanism of mechanical effect and fungal action (CM > 90%).

CONCLUSION

The efficacy of Bb gel systems was assessed according to its properties in favouring the growth and vitality of Bb as well as in reducing the Ae. albopictus hatching eggs rate. Further studies, in semi-field and field conditions, will be useful to evaluate the efficacy of Bb/Gel systems on adults in terms of attraction, oviposition, mortality, and potential autodissemination to propose a new tool in precision pest management. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Global climate change and its impact on the distribution and efficacy of Bacillus thuringiensis as a biopesticide

This study is the first modeling exercise to assess the impacts of climate change on the current and future global distribution of Bacillus thuringiensis (Bt). Bt is a common Gram-positive, rod-shaped bacterium widely distributed in various environments, including soil and water. It is widely recognized as a source of effective and safe agricultural biopesticides for pest management in various climatic regions globally. In the present work, ensemble species distribution models were developed for Bt based on the generalized linear model (GLM), generalized boosting model (GBM), random forest (RF), and maximum entropy (MaxEnt) under two distinct scenarios, SSP2-4.5 (optimistic) and SSP5-8.5 (pessimistic) for the year of 2050, 2070, and 2090. The performance of our models was evaluated based on true skill statistics (TSS) and the area under the receiver-operator curve (AUC) indices. Both AUC and TSS values were observed in an acceptable range, with AUC at 0.84 and TSS at 0.512, respectively. Results indicate that most of the areas currently suitable for Bt will likely remain stable in the future, particularly Central America, Central and South Africa, South Asia, and parts of Oceania. Norway, Peru, and the UK will have notable habitat gains by 2090 based on SSP2-4.5 and SSP5-8.5 scenarios. On the contrary, Serbia, Guinea, Poland, Croatia, Spain and Romania showed notable losses under both scenarios. Our results underscore Bt potential to improve pest control, crop yields, and environmental sustainability, especially in regions where agriculture is predominant. Our research highlights the need to understand ecological dynamics for future conservation and agricultural planning in the face of climate change.

Insecticidal activities of three recombinant venom proteins of the predatory stink bug, Arma custos

BACKGROUND

Widespread resistance of insect pests to insecticides and transgenic crops in the field is a significant challenge for sustainable agriculture, and calls for the development of novel alternative strategies to control insect pests. One potential resource for the discovery of novel insecticidal molecules is natural toxins, particularly those derived from the venoms of insect predators.

RESULTS

In this study, we identified three insecticidal proteinaceous toxins from the venom glands (VGs) of the predatory stink bug, Arma custos (Hemiptera: Asopinae). Transcriptomic analysis of A. custos VGs revealed 151 potentially secreted VG-rich venom proteins. Three VG-rich venom proteins (designated AcVP1 ~ 3) were produced by overexpression in Escherichia coli. Injection of the recombinant proteins into tobacco cutworm (Spodoptera litura) larvae showed that all of the three recombinant proteins caused paralysis, liquefaction and death. Injection of recombinant proteins into rice brown planthopper (Nilaparvata lugens) nymphs showed higher insecticidal activities, among which a trypsin (AcVP2) caused 100% mortality postinjection at 1.27 pmol mg-1 body weight.

CONCLUSION

A natural toolkit for the discovery of insecticidal toxins from predatory insects has been revealed by the present study. © 2024 Society of Chemical Industry.

Biocontrol agents and their potential use as nano biopesticides to control the tea red spider mite (Oligonychus coffeae): A comprehensive review

Tea red spider mite (TRSM), Oligonychus coffeae Nietner, is one of the major pests that cause considerable crop losses in all tea-growing countries. TRSM management often involves the use of multiple chemical pesticides that are linked to human health risks and environmental pollution. Considering these critical issues, employing biocontrol agents is a potential green approach that may replace synthetic pesticides. This review study aims to discuss the efficacy of plant extracts, entomopathogenic microorganisms, and predators in controlling TRSM. This study includes 44 botanical extracts, 14 microbial species, and 8 potential predators used to control TRSM, along with their respective modes of action. Most of the botanical extracts have ovicidal, adulticidal, and larvicidal activity, ranging from 80 to 100 %, attributed to bioactive compounds such as phenols, alcohols, alkaloids, tannins, and other secondary metabolites. Among microbial pesticides, Purpureocillium lilacinum, Metarhizium robertsii, Aspergillus niger, Pseudomonas fluorescens, and Pseudomonas putida are highly effective against TRSM without causing any harm to the nontarget beneficial insects. Besides, some predators, including green lacewings, ladybirds, and phytoseiid mites have the potential to control TRSM. Employing these biocontrol agents simultaneously in tea plantations could be more effective in preventing TRSM. Nevertheless, their high biodegradability rate, uneven distribution, and uncontrolled release pose challenges for large-scale field applications. This study also explores how nanotechnology can enhance sustainability by addressing the limitations of biopesticides in field conditions. This review study could contribute to the search for potential biocontrol agents and the development of commercial nano biopesticides to control TRSM.

Relative activity of 15 bacterial strains against the larvae of Helicoverpa armigera, Spodoptera exigua, and Spodoptera litura (Lepidoptera: Noctuidae)

Crystal toxins produced by different strains of entomopathogenic Bacillus thuringiensis (Bt) have been characterized and widely applied as commercial biological pesticides owing to their excellent insecticidal properties. This study aimed to identify novel bacterial strains effective in controlling Spodoptera exigua Hübner, Helicoverpa armigera Hübner, and Spodoptera litura Fabricius. Fifteen culturable bacterial strains were isolated from 60 dead larvae (H. armigera and S. exigua) collected in the field. The biochemical characteristics and 16S rRNA sequences of these strains indicated that one strain (B7) was Lysinibacillus sp., 12 strains (B1, B3, B4, B5, B6, B8, P2, P3, P4, P5, P6, and DW) were Bt kurstaki, and P2-2 and B2 were Bacillus velezensis subsp. Laboratory bioassays indicated that strains B3, P6, B6, and P4 showed high toxicity to second-instar larvae of S. exigua, with LC50 values of 5.11, 6.74, 205.82, and 595.93 µg/ml, respectively; while the strains P5, B5, B6, and P6, were the most efficient against second-instar larvae of H. armigera with LC50 values of 725.82, 11,022.72, 1,282.90, 2,005.28, respectively, and strains DW, P3, P2, and B4 had high insecticidal activity against second-instar larvae of S. litura with LC50 values of 576.69, 1,660.96, 6,309.42, and 5,486.10 µg/ml, respectively. In conclusion, several Bt kurstaki strains with good toxicity potential were isolated and identified in this study. These strains are expected to be useful for biointensive integrated pest management programs to reduce the use of synthetic insecticides.

Phytostimulation and biocontrol potential of Gram-positive endospore-forming Bacilli

The spore-forming Bacillus and Paenibacillus species represent the phyla of beneficial bacteria for application as agricultural inputs in form of effective phytostimulators, biofertilizers, and biocontrol agents. The members of the genera Bacillus and Paenibacillus isolated from several ecological habitats are been thoroughly dissected for their effective application in the development of sustainable and eco-friendly agriculture. Numerous Bacillus and Paenibacillus species are reported as plant growth-promoting bacteria influencing the health and productivity of the food crops. This review narrates the mechanisms utilized by these species to enhance bioavailability and/or facilitate the acquisition of nutrients by the host plant, modulate plant hormones, stimulate host defense and stress resistance mechanisms, exert antagonistic action against soil and airborne pathogens, and alleviate the plant health. The mechanisms employed by Bacillus and Paenibacillus are seldom mutually exclusive. The comprehensive and systematic exploration of the aforementioned mechanisms in conjunction with the field investigations may assist in the exploration and selection of an effective biofertilizer and a biocontrol agent. This review aims to gather and discuss the literature citing the applications of Bacillus and Paenibacillus in the management of sustainable agriculture.