Letteratura scientifica selezionata sul tema "Bioinsecticides Bt"

Bioinsecticides made from the bacterium Bacillus thuringiensis (Bt) are the bestselling bioinsecticide worldwide. Among Bt bioinsecticides, those based on the strain Bt subsp. kurstaki (Btk) are widely used in farming to specifically control pest lepidopteran larvae. Although there is much evidence of the lack of acute lethality of Btk products for non-target animals, only scarce data are available on their potential non-lethal developmental adverse effects. Using a concentration that could be reached in the field upon sprayings, we show that Btk products impair growth and developmental time of the non-target dipteran Drosophila melanogaster. We demonstrate that these effects are mediated by the synergy between Btk bacteria and Btk insecticidal toxins. We further show that Btk bioinsecticides trigger intestinal cell death and alter protein digestion without modifying the food intake and feeding behavior of the larvae. Interestingly, these harmful effects can be mitigated by a protein-rich diet or by adding the probiotic bacterium Lactobacillus plantarum into the food. Finally, we unravel two new cellular mechanisms allowing the larval midgut to maintain its integrity upon Btk aggression: First the flattening of surviving enterocytes and second, the generation of new immature cells arising from the adult midgut precursor cells. Together, these mechanisms participate to quickly fill in the holes left by the dying enterocytes.

Drosophila suzukii, Spotted Wing Drosophila (SWD), is a serious economic issue for thin-skinned fruit farmers. The invasion of this dipteran is mainly counteracted by chemical control methods; however, it would be desirable to replace them with biological control. All assays were performed with Bacillus thuringiensis (Bt), Xenorhabdus nematophila (Xn), and Xn secretions, administered orally in single or combination, then larval lethality was assessed at different times. Gut damage caused by Bt and the influence on Xn into the hemocoelic cavity was also evaluated. In addition, the hemolymph cell population was analyzed after treatments. The data obtained show that the combined use of Bt plus Xn secretions on larvae, compared to single administration of bacteria, significantly improved the efficacy and reduced the time of treatments. The results confirm the destructive action of Bt on the gut of SWD larvae, and that Bt-induced alteration promotes the passage of Xn to the hemocoel cavity. Furthermore, hemocytes decrease after bioinsecticides treatments. Our study demonstrates that combining bioinsecticides can improve the efficacy of biocontrol and such combinations should be tested in greenhouse and in field in the near future.

About 10% of angiosperms, an estimated 20,000 species, produce latex from ubiquitous isoprene precursors. Latex, an aqueous suspension of rubber particles and other compounds, functions as an antifeedant and herbivory deterrent. It is soluble in neutral to alkaline pH, and coagulates in acidic environments. Here, I propose that foregut-fermenting herbivores such as ruminants, kangaroos, sloths, insect larvae, and tadpoles have adapted to latex in forage with the evolution of alkaline anterior digestive chamber(s). However, they consequently become susceptible to the action of Bacillus thuringiensis (Bt) δ-endotoxin and related bioinsecticides which are activated in alkaline environments. By contrast, hindgut-fermenting herbivores, such as horses and rabbits, have acidic anterior digestive chambers, in which latex coagulates and may cause gut blockage, but in which Bt is not activated. The latex-adapted foregut herbivore vs. latex-maladapted hindgut herbivore hypothesis developed in this paper has implications for hindgut-fermenting livestock and zoo animals which may be provided with latex-containing forage that is detrimental to their gut health. Further, ruminants and herbivorous tadpoles with alkaline anterior chambers are at risk of damage by the supposedly “environmentally friendly” Bt bioinsecticide, which is widely disseminated or engineered into crops which may enter animal feed streams.

Bacillus thuringiensis (Bt) is an ubiquitous Gram positive, spore forming bacterium that forms parasporal crystal inclusions. These proteinaceous inclusions are called crystal (Cry) proteins or delta- endotoxins, which are toxic to insects. Hence preparations of Bt are being used as bioinsecticides for the past four decades in commercial agriculture and forest management for the control of certain insect species belonging to the orders of Lepidoptera, Diptera and Coleoptera. Bt is a major source for transfer of genes into plants to impart insect resistance. Since 1996 millions of hectares are grown with insect resistant transgenic plants containing Bt genes, in different parts of the world. Commercial release of transgenic Bt cotton in India is expected soon.

Many insects, including the Plutella xylostella (L.), have developed varying degrees of resistance to many insecticides, including Bacillus thuringiensis (Bt) toxins, the bioinsecticides derived from Bt. The polycalin protein is one of the potential receptors for Bt toxins, and previous studies have confirmed that the Cry1Ac toxin can bind to the polycalin protein of P. xylostella, but whether polycalin is associated with the resistance of Bt toxins remains controversial. In this study, we compared the midgut of larvae from Cry1Ac-susceptible and -resistant strains, and found that the expression of the Pxpolycalin gene was largely reduced in the midgut of the resistant strains. Moreover, the spatial and temporal expression patterns of Pxpolycalin showed that it was mainly expressed in the larval stage and midgut tissue. However, genetic linkage experiments showed that the Pxpolycalin gene and its transcript level were not linked to Cry1Ac resistance, whereas both the PxABCC2 gene and its transcript levels were linked to Cry1Ac resistance. The larvae fed on a diet containing the Cry1Ac toxin showed no significant change in the expression of the Pxpolycalin gene in a short term. Furthermore, the knockout of polycalin and ATP-binding cassette transporter subfamily C2 (ABCC2) genes separately by CRISPR/Cas9 technology resulted in resistance to decreased susceptibility to Cry1Ac toxin. Our results provide new insights into the potential role of polycalin and ABCC2 proteins in Cry1Ac resistance and the mechanism underlying the resistance of insects to Bt toxins.

The effectiveness of pre-sowing treatment of soybean seeds and application of biorational insecticides in reducing the number of major pests of soybean in the conditions of the Primorsky Territory have been studied. The results of using insecticides and biopreparations to regulate the number of dominant pests of soybean have been presented. The studies were conducted in 2020 and 2021. The efficiency of insecticidal protectants Imidor Pro, SC (2 l/t) and Tabu, WSC (1.0 l/t), bioinsecticides Fitoverm, EC (0, 16 l/ha), Proclaim, WSG (0.3 kg/ha), Batsikol, L (15 l/ha), Biosleep BW, L (2 l/ha), Biosleep BT, P (2 kg/ha) against two-striped leaf beetle (Medythia nigrobilineatus Motsch.) and soybean pod borer (Leguminivora glycinivorella Mats.) were studied. Pre-sowing seed treatment with insecticides Imidor Pro and Tabu reduced damage of soybean plants in the sprouting phase by Medythia nigrobilineatus beetles compared to the control by 94.0–98.2%. Seed dressing with imidacloprid-based preparations provided effective protection of crops against the pest in the sprouting – branching phase. Biorational insecticides based on avermectin C and Bacillus thuringiensis showed high biological efficacy (71.1–98.8%) on the 5–10th day after treatment against the two-striped leaf beetle. Soybean seed damage when bioinsecticides were used against Leguminivora glycinivorella was 1.9–3.0% compared to 5.6% in the control. The conducted studies testify to the prospect of using the preparations of biological origin to control the number of dominant pests in soybean crops.

Bacillus thuringiensis (Bt) Berliner has potential for use in insect management. Its use can be an alternative for the management of Bradysia aff. ocellaris (Comstock), considered one of the main strawberry pests in a soilless system. Therefore, the objective of this work was to evaluate the toxicity of different bacteria on B. aff. ocellaris in laboratory and greenhouse bioassays. The following isolates were used in the experiments: Bacillus circulans (Bc), B. thuringiensis var. oswaldo cruzi (Bto) or B. thuringiensis var. israelensis (Bti) and B. thuringiensis var. kurstaki (Btk) In the laboratory, B. aff. ocellaris larvae showed high susceptibility to Bti isolate (92 % mortality) 14 days after treatment exposure (DAET). In contrast, the isolates Bc, Bto, and Btk showed less than 32 % mortality, not differing from the control treatment (water – 22 % mortality). According to the concentration-response curves the values of lethal concentration LC50 and LC90 were 4 x 106 CFU.mL-1 and 4 x 1015 CFU.mL-1. By applying Bti (4 × 1012 CFU.mL-1) at the base of strawberry plants growing in plastic pots containing commercial plant substrate, a reduction of 26 % in the emergence of B. aff. ocellaris was observed. According to these results, the Bti isolate is considered promising for the formulation of bioinsecticides based on Bt for the management of B. aff. ocellaris in strawberry culture.

Anticarsia gemmatalis Hübner, 1818 is the main soybean defoliating pest in Brazil. The biological control of the species is done with products based on toxins produced by Bacillus thurigiensis (Bt), as bioinsecticides, or in transgenic plants. After activation by intestinal proteases, these toxins interact with receptors, especially cadherin, leading to death due to the formation of cellular pores. In recent years resistant populations have been identified in the laboratory, which can be a problem if the same patterns are found in crops, reducing their control effect. In this paper, we performed a comparative structural analysis of a mutation region for the gene of this receptor in A. gemmatalis, among resistant and susceptible strains treated with a toxin produced by Bt (Cry1Ac). The HaCad fragment of the cadherin gene was amplified by PCR, sequenced, and analyzed by bioinformatics tools. The PCR results were positive for resistant specimens but not for susceptible strains, suggesting the presence of a mutation in the resistant strain. In the sequenced fragments of the resistant insects, six haplotypes were found, and the originated amino acid sequences demonstrated the modification in four sites, which did not interfere with the three-dimensional shape of the protein. These data showed considerable variation taking into account the size of the fragment, even if they do not affect the final structure of the protein. The results allowed a better understanding of the mechanisms of resistance to Cry1Ac in the species, mainly in the involvement of cadherin in this process.

L'intestin est un organe multifonctionnel complexe faisant partie du système digestif. Pour maintenir son intégrité et ses différentes fonctions (digestives, absorbantes, immunitaires, endocriniennes), l'épithélium intestinal doit faire aux agressions quotidiennes provenant des aliments, des métabolites, du microbiote, des pathogènes ou des molécules chimiques ingérés. L'épithélium intestinal étant une unique couche cellulaire, il doit lutter en permanence pour garder son intégrité et ses fonctions. Pour y parvenir, les cellules souches intestinales (ISC) permettent à l'intestin de générer de nouvelles cellules remplaçant celles lésées, âgées ou mortes, maintenant l'homéostasie tout en limitant le risque de développer des pathologies telles que les maladies inflammatoires et les cancers.Mes travaux de thèse s'appuient sur l'intestin de Drosophila melanogaster, modèle reconnu pour étudier les mécanismes d'homéostasie intestinale et la biologie des cellules souches adultes. Dans un premier projet, j'ai analysé le rôle des protéines du groupe Polycomb (PcG) dans les ISC. J'ai également, dans un deuxième projet, étudié les effets de l'ingestion chronique d'insecticides à base de la bactérie Bacillus thuringiensis (Bt) sur le développement de maladies intestinales.Les protéines PcG participent à l'organisation 3D du génome et au contrôle de l'expression génique. Les PcG et leurs mécanismes sont conservés des plantes aux mammifères et ont d'abord été identifiés comme régulateurs dans les processus de développement. Plus tard, les PcG ont été décrits comme impliqués dans divers processus, notamment la régulation des cellules souches adultes. Les activités d'ubiquitination et de triméthylation de deux complexes répressifs Polycomb majeurs, PRC1 et 2, conduisent à la propagation et au maintien de la répression génique en compactant la chromatine. J'ai montré par des expériences de perte de fonction que PRC1 et PRC2 permettent le maintien de l'identité des ISC et de leur capacité à générer des cellules différenciées. En effet, les ISC mutantes perdent les marqueurs cellules souches et forment des tumeurs néoplasiques. En étudiant différentes voies de signalisation, j'ai identifié la voie JAK/STAT comme étant activée dans les tumeurs générées. Les protéines PcG impacte donc directement l'homéostasie intestinale en agissant comme suppresseur de tumeur dans les ISC.En condition défavorable, le genre Bacillus a la particularité de former un état de dormance extrêmement résistant, la spore. La réponse de l'intestin face aux spores de bactéries a été très peu étudiée et fait l'originalité de la thématique de l'équipe. Sous forme de spores, Bt est le bioinsecticide le plus utilisé en agriculture comme méthode alternative aux pesticides chimiques pour protéger les cultures des ravageurs. Bt est génétiquement très proche de B. cereus (Bc), qui est le deuxième agent responsable de toxi-infections alimentaires collectives (TIAC) en France. Alors que l'impact de Bt sur les organismes non-cibles est controversé, des études récentes suggèrent que certaines TIAC pourraient être attribuées à des souches de Bt d'origine agricole. Ainsi, mon deuxième projet avait pour objectif d'évaluer si la présence répétée de Bt dans l'intestin via l'alimentation pouvait induire un contexte pathologique. Nous avons montré que l'ingestion chronique de Bt, à des doses agricoles, induit une dysplasie précoce et un vieillissement prématuré de l'intestin. J'ai également montré que ce phénomène était aggravé chez des drosophiles génétiquement prédisposées à développer des maladies inflammatoires. Ainsi, ce travail permet une première évaluation des risques de maladies intestinales liées à la consommation chronique d'insecticides Bt
The intestine is a complex multifunctional organ that is part of the digestive system. To maintain its integrity and its various functions (digestive, absorbent, immune, endocrine), the intestinal epithelium must deal with daily aggressions from food, metabolites, microbiota, pathogens or chemical molecules that are ingested. Since the intestinal epithelium is a single-cell layer, it must constantly fight to maintain its integrity and functions. To achieve this, intestinal stem cells (ISC) allow the intestine to generate new cells to replace injured, old or dead ones, maintaining homeostasis while limiting the risk of developing pathologies such as inflammatory diseases and cancers. My thesis work relies on the intestine of Drosophila melanogaster, a recognized model for studying intestinal homeostasis mechanisms and adult stem cell biology. In a first project, I analyzed the role of Polycomb group (PcG) proteins in ISC. In a second project, I also studied the effects of chronic ingestion of Bacillus thuringiensis (Bt) insecticides on the development of intestinal diseases.PcG proteins participate in the genome 3D organization and in gene expression control. PcG and their mechanisms are conserved from plants to mammals and were first identified as regulators in developmental processes. Later, PcG were described as involved in various processes, including the regulation of adult stem cells. The ubiquitination and trimethylation activities of the two major Polycomb repressive complexes, PRC1 and 2, lead to the propagation and maintenance of gene repression by chromatin compaction. Through loss-of-function experiments, I have shown that PRC1 and PRC2 allow the maintenance of ISC identity and their ability to generate differentiated cells. Indeed, ISC mutant lose stem cell markers and form neoplastic tumors. By studying different signaling pathways, I identified the JAK/STAT pathway as being activated in the resulting tumors. PcG proteins therefore directly impact gut homeostasis by acting as tumor suppressors in ISCs.In unfavorable conditions, the Bacillus genus can form an extremely resistant state of dormancy, the spore. The intestinal response to bacterial spores has been poorly studied and makes the originality of the team's work. In the form of spores, Bt is the most widely used bioinsecticide in agriculture as an alternative method to chemical pesticides to protect crops from pests. Bt is genetically very close to B. cereus (Bc), which is the second agent responsible for foodborne outbreaks (FBO) in France. While the impact of Bt on non-target organisms is controversial, recent studies suggest that some FBO could be attributed to Bt strains from agriculture. Thus, my second project aimed to assess whether the repeated presence of Bt in the intestine through the food could induce a pathological context. We have shown that Bt chronic ingestion, at agricultural doses, induces early dysplasia and premature aging of the gut. I also showed that this phenomenon was aggravated in fruit flies genetically predisposed to develop inflammatory diseases. Thus, this work provides a first assessment of the risks of intestinal diseases linked to the chronic consumption of Bt insecticides

Orientador: Marcelo da Costa Ferreira
Resumo: O algodão (Gossypium hirsutum L.) tem grande relevância para a economia mundial. Dentre os principiais fatores limitantes da produção estão os problemas fitossanitários, que ocorrem em todas as fases da cultura. O inseto Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) é importante devido a sua capacidade de causar danos nas folhas e maçãs do algodoeiro, muitas vezes requerendo a aplicação frequente de inseticidas para o seu controle. Em geral são utilizados inseticidas químicos. Entretanto, o uso de bioinseticidas têm aumentado consistentemente, principalmente aqueles à base de Bacillus thuringiensis, chamados de Bt bioinseticidas. Fatores abióticos como a chuva também interferem na eficiência de aplicações de Bt bioinseticidas e consequentemente no controle do organismo alvo. Uma alternativa que pode dar proteção ao Bt mediante chuva é a adição de adjuvantes a calda. Porém, pouco se sabe o quanto a associação do Bt com adjuvantes afeta no crescimento vegetativo, esporulação e persistência da bactéria e o controle. Portanto é de extrema importância à compreensão das interações físico-químicas e biológicas da mistura de Bt bioinseticidas e adjuvantes. Neste contexto, objetivou-se avaliar o efeito da adição de adjuvantes nas características físico-química e biológicas dos Bt bioinseticidas nas formulações Dipel® WP e Dipel® SC submetidas à chuva artificial para o controle de S. frugiperda em plantas de algodão. Para simular a chuva, foram utilizadas as lâminas de chuv... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Cotton (Gossypium hirsutum L.) has great relevance to the world economy. Among the main limiting factors of production are the phytosanitary problems that occur at all stages of the crop. The insect Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae) is important because of its ability to cause damage to cotton leaves and apples, often requiring insecticides to be applied frequently for its control. In general, chemical insecticides are used. However, the use of bioinsecticides has consistently increased, especially those based on Bacillus thuringiensis, called Bt bioinsecticides. Abiotic factors such as rain also interfere with the efficiency of Bt applications and consequently in the control of the target organism. An alternative that can protect Bt in the rain is the addition of adjuvants to the syrup. However, little is known about how the association of Bt with adjuvants affects vegetative growth, sporulation and bacterial persistence and control. Therefore, it is extremely important to understand the physicochemical and biological interactions of the mixture of Bt bioinsecticides and adjuvants. In this context, the objective of this study was to evaluate the effect of the addition of adjuvants on the physicochemical and biological characteristics of Bt bioinsecticides in the formulations Dipel® WP and Dipel® SC submitted to artificial rain to control S. frugiperda in cotton plants. To simulate the rain, the 20mm artificial rain blades applied one hour after the ap... (Complete abstract click electronic access below)
Doutor

Bacillus thuringiensis (Bt) est une bactérie sporulante Gram-positive. Elle a synthétise des toxines (Cry) entomopathogènes qui sont enfermées dans un cristal au sein de la spore. Les produits Bt sont les bioinsecticides les plus efficaces contre les lépidoptères ravageurs de cultures et prédominent en agriculture biologique, occupant 70 % des parts de marché des bioinsecticides. La surface mondiale en agriculture biologique a doublé en 10 ans induisant de facto une augmentation de 4% par an de l'utilisation des bioinsecticides. Cette tendance va s'accentuer dans les années à venir suite aux incitations nationales et internationales visant à réduire l’utilisation des produits chimiques. Avec cette forte croissance, les populations sont de plus en plus exposées aux bioinsecticides via l’alimentation, ce qui soulève la question de leurs effets potentiels à long terme sur la santé. Le premier organe en contact avec de la nourriture contaminée par les bioinsecticides Bt est donc le tube digestif.Mon projet de thèse s'intéresse aux conséquences physiopathologiques intestinales liées à l'ingestion chronique de Bt aux doses retrouvées sur les légumes "bio" après traitement en utilisant la drosophile comme modèle. La drosophile permet d'identifier les mécanismes physiologiques, cellulaires et génétiques impliqués dans les effets observés. La conservation de ces mécanismes entre la drosophile et les vertébrés permet ensuite de rapidement aborder les problèmes chez les mammifères. J'ai ainsi montré que l'ingestion de bioinsecticides Btk kurstaki (Btk) aux doses environnementales par des drosophiles adultes induisait sous 24h une apoptose modérée des entérocytes. J'ai montré que cette apoptose est causée par les toxines Cry de Btk. Qui dit apoptose d'entérocytes, dit mise en route du processus de remplacement cellulaire via la différentiation des progéniteurs en entéroblastes puis en entérocytes. Etonnamment, j'ai observé une forte augmentation du nombre de cellules entéroendocrines à partir du premier jour suivant l'ingestion. Par lignage cellulaire, j'ai démontré que peu de nouveaux entérocytes apparaissaient, en tous cas pas suffisamment pour remplacer tous ceux mourant. De fait, le nombre total d'entérocytes dans l'intestin diminue alors que le nombre de cellules entéroendocrine augmente. Ensuite j'ai démontré que les cristaux de toxines de Btk détournaient les progéniteurs de leur destin initial d'entérocytes vers un destin de cellules entéroendocrines, à cause d'un affaiblissement de l'interaction cellule-cellule entre les cellules souches intestinales mères et les cellules filles progénitrices. J'ai pu sauver l'excès de cellules entéroendocrines dépendant du bioinsecticides Btk en augmentant la force des jonctions adhérentes entre les cellules souches et les progéniteurs. La souche Btk composant les produits commerciaux produit 5 toxines Cry différentes (Cry1Aa, Cry1Ab, Cry1Ac, Cry2Aa, et Cry2Ab) ciblant les larves de lépidoptères. J'ai montré que les toxines de type Cry1A sont capables, seules, d'induire l'augmentation du nombre de cellules entéroendocrines.En conclusion, une partie de mes travaux participent aux connaissances sur les mécanismes physiologiques, génétiques et cellulaires fondamentaux nécessaires au maintien de l'intégrité de l'épithélium intestinale après une agression modérée. D'autre part, mes travaux montrent que l’ingestion de bioinsecticides Btk aux doses utilisées en agriculture induit une perturbation de l’équilibre physiologique de l'intestin d'un organisme non-cible. La poursuite de ce type de travaux est essentielle pour arriver à évaluer minutieusement les risques consécutifs à une exposition aux biopesticides Btk par les organismes non-cibles. Il est important d’obtenir des données précises pour mettre en place des mesures préventives et/ou curatives pour la santé humaine et l'environnement
Microbes, toxins and chemicals such as pesticides are harmful agents that could attack the gastrointestinal tract throughout organismal life. This triggers a rapid renewing of damaged intestinal cells to sustain a functional barrier to limit the risk of developing pathologies. The repair process involves a transient proliferation of intestinal stem cells (ISCs) and the differentiation of their progeny into enterocytes to replace the damaged ones. Among pesticides, the broadly used bioinsecticides composed of spores and crystalline (Cry) toxins of Bacillus thuringiensis subsp kurstaki (Btk) are expected to supplant synthetic chemical pesticides to specifically fight lepidopteran pests. We have investigated here the effects of spores and toxins of Btk ingested along with the food on intestinal cellular homeostasis of the non-target dipteran Drosophila melanogaster. We showed that Btk Cry toxins induce enterocyte death and ISC proliferation. Surprisingly, a high proportion of ISC's daughter cells differentiate into enteroendocrine cells instead of their initial enterocyte destiny. This imbalanced intestinal cell composition is due to Cry toxins which weakened cell adhesion between the ISC mother cell and its immediate daughter progenitor leading the latter to adopt an enteroendocrine cell fate. Our results further showed that Cry1A family of toxins is implicated in this intestinal cell fate diversion, suggesting that Btk bioinsecticides induce non-negligible deleterious effects on gut physiology