The bacterium Bacillus thuringiensis (Bt) produces delta-endotoxins that possess toxic properties and can be used as biopesticides, as well as a source of genes for the construction of transgenic plants resistant to insects. In Brazil, the introduction of Bt soybean with insecticidal properties to the velvetbean caterpillar, the main insect pest of soybean, has been seen a promising tool in the management of these agroecosystems. However, the increase in stink bug populations in this culture, in various regions of the country, which are not susceptible to the existing genetically modified plants, requires application of chemicals that damage the environment. Little is known about the actual toxicity of Bt to Hemiptera, since these insects present sucking mouthparts, which hamper toxicity assays with artificial diets containing toxins of this bacterium. In recent studies of cytotoxicity with the gut of different hemipterans, susceptibility in the mechanism of action of delta-endotoxins has been demonstrated, which can generate promising subsidies for the control of these insect pests in soybean. This paper aims to review the studies related to the selection, application and mode of action of Bt in the biological control of the major pest of soybean, Anticarsia gemmatalis, and an analysis of advances in research on the use of Bt for control hemipterans.

ResumoAs substâncias repelentes ou atraentes das plantas são, principalmente, de natureza terpênica e se apresentam como moléculas de baixo peso molecular e volátil. Essas substâncias, normalmente, são conhecidas como aromáticas e se denominam óleos essenciais, os quais se acumulam em todos os órgãos vegetais. Nos vegetais, os óleos essenciais desenvolvem funções relacionadas com sua volatilidade, agindo na atração de polinizadores, na proteção contra predadores, nos patógenos, na perda de água, no aumento de temperatura e também desempenhando funções ecológicas, especialmente como inibidoras de germinação. Essas características tornam as plantas que os produzem poderosas fontes de agentes biocidas, o que é largamente estudado nos agroecossistemas, principalmente no que concerne às ações bactericida, fungicida e inseticida. Os óleos essenciais têm como principais constituintes os monoterpenos, seguidos pelos sesquiterpenos, além de compostos aromáticos de baixo peso molecular. Sua função específi ca na planta ainda é desconhecida, porém se acredita que, durante o seu desenvolvimento, as plantas superiores sintetizam terpenóides essenciais para o próprio crescimento. Essas substâncias do metabolismo secundário podem agir como inibidores de germinação, proteção contra predadores, atração de polinizadores, entre outras. Entretanto, a avaliação desses compostos com fi nalidades diversas, como, por exemplo, no controle de microrganismos patogênicos de plantas cultivadas ou, ainda, como inseticida ou herbicida natural, é recente, visto que são poucos os trabalhos de pesquisa desenvolvidos e publicados nessa área. Esta revisão em artigo trata das interações dos óleos essenciais de plantas medicinais, silvestres e cultivadas com microrganismos e insetos.Palavras-chave: óleos essenciais, insetos, fungos, bactérias. AbstractThe repelling or attracting plants substances are mainly from terpenic nature and they appear as molecules with less molecular weight and volatile. Usually, these substances are known as aromatic or essential oils, which amass themselves at all herbal organs. In the herbs, essential oils develop functions related to volatility, acting to attract the pollinating, to protect against pathogens predators, in the missing of water, to rise the temperature and also making ecological functions, especially as a germination inhibitor. These features make the plants which produce these aromatics a powerful source of biocidal agents, being steadily studied in agroecosystems, principally because of the bactericidal, fungicidal, and insecticidal activities. The main components are the monoterpenes, followed by sesquiterpenes, besides aromatic compounds with low molecular weight. The specifi c function that essential oils turns out on the plant is still unknown; however, it is supposed that the higher plants synthesize terpenoids which are essential to their growth. These substances of secondary metabolism can act as germination inhibitors, protection against predators, pollinator attractors, among others. However, t...

The endophytic bacteria belong to a larger group of microorganisms that have their life-cycle partly or entirely inside the plant and are located in intra and inter-cellular spaces or in the vascular tissue. These bacteria can be found colonizing aerial parts or roots. This review aims to analyze the colonization strategies of endophytic bacteria through interaction with plants, as well as to highlight the metabolic influence of these organisms in plant tissues, which result in physiological and biochemical changes. Depending on the different mechanisms used internally to colonize a plant, these microorganisms are called obligate, facultative, or passive endophytes. Phytostimulation, biofertilization and biological control are mechanisms that result in the development of the plant through the production of plant hormones, bioavailability of nutrients and antagonistic action to phytopathogens, respectively. The association between endophytic bacteria and plants features important benefits such as significant increases in growth, plant biomass, length of roots, dry matter production, and grain yield. Studies show that there is a great diversity of endophytic bacteria colonizing plant structures that result in several benefits to the host plant.

Toxic effects of essential plant oils in adult Sitophilus oryzae (Linnaeus) (Coleoptera, Curculionidae). Stored grains are subject to losses in quality nutritional value and in sanitation from the time they are stored to the time they are consumed. Botanical insecticides may offer an alternative solution for pest control. The objective was to test the insecticidal properties of the essential oils of Cymbopogon citratus (leaf), Zingiber officinale (root) and Mentha sp. (leaf). The efficacy of these oils was tested to control the rice weevil, S. oryzae, using hydrodistillation. Chemical analysis of the essential oils was carried out by gas chromatography. Major components of C. citratus were geranial (48%) and neral (31%), of Z. officinale were α-zingibereno (13%), geranial (16%), neral (10%) and α-farneseno (5%) and of Mentha sp. was menthol (92%). Bioassays were carried out by fumigation and topical application. In topical application assays, the essential oil of C. citratus had greater toxicity (LC50 0.027 µL mL-1) and shorter exposure time than the oils of the other two plants. After 24 h and 48 h, 70% and 100% mortality of S. oryzae occurred, respectively. In fumigation assays, essential oil of Z. officinale had a lower LC50 (1.18 µL cm-2) and 70% mortality after 24 h exposure. Therefore, we recommend the use of essential oils of C. citratus and Z. officinale to control the rice weevil S. oryzae.
Efeito tóxico de óleos essenciais de plantas medicinais em adultos de Sitophilus oryzae (Linnaeus) (Coleoptera, Curculionidae). Grãos armazenados estão sujeitos a perdas na qualidade física, sanitária e nutricional, desde sua maturação fisiológica até o momento do consumo. Uma alternativa para o manejo de pragas são os inseticidas botânicos. O presente trabalho teve como objetivo avaliar o efeito inseticida de óleos essenciais de Cymbopogon citratus (folha), Zingiber officinale (raiz) e Mentha sp. (folha), obtidos através do método de hidrodestilação,no controle de adultos do gorgulho-do-arroz, S. oryzae. A caracterização química dos compostos encontrados nos óleos essenciais foi realizada por cromatografia gasosa, sendo observados como principais componentes para C. citratus: geranial (48%) e neral (31%), para Z. officinale: 16% de geranial, 13% de α-zingibereno, 10% de neral e 5% de α-farneseno e para Mentha sp.: 92% de mentol. Os bioensaios foram realizados por aplicação tópica e fumigação. Os resultados da aplicação tópica mostraram que o óleo essencial de C. citratus apresenta maior toxicidade quando comparado à Mentha sp.e ao Z. officinale, pois apresentou uma CL50 de 0.027 µL mL-2 e um menor período de exposição, causando 70% e 100% de mortalidade de adultos de S. oryzae, respectivamente, 24 e 48 horas após dos tratamentos. Nos ensaios com fumigação, em adultos de S. oryzae, o óleo essencial de Z. officinale, apresentou a menor CL50 (1,18 µL cm-2) e o menor período de exposição, causando 70% de mortalidade em 24 horas após a aplicação dos tratamentos. Desse modo conclui-se que os óleos de...

RESUMO Esta publicação apresenta alguns dados sobre as interações entre as bactérias e as plantas hospedeiras, considerando os simbiontes e os patógenos das plantas de importância agrícola, com ênfase nos agroecossistemas de arroz irrigado. Neste trabalho foram abordados aspectos relacionados a essas bactérias endofíticas, tais como: (i) endofíticos e suas interações com as plantas cultivadas; (ii) rizobactérias promotoras do crescimento vegetal [plant growth-promoting rhizobacteria (PGPR)] e sua aplicabilidade no controle biológico; (iii) bactérias endofíticas versus PGPR no controle biológico de fitopatógenos; (iv) aplicação de recombinantes endofíticos na agrobiotecnologia. No final do artigo estão apresentadas as opiniões e perspectivas dos autores sobre as bactérias que vivem associadas às plantas cultivadas nos agroecossistemas.

Among the phytophagous insects which attack crops, the fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera, Noctuidae) is particularly harmful in the initial growth phase of rice plants. As a potential means of controlling this pest, and considering that the entomopathogen Bacillus thuringiensis Berliner demonstrates toxicity due to synthesis of the Cry protein, the present study was undertaken to evaluate this toxic effect of B. thuringiensis thuringiensis 407 (pH 408) and B. thuringiensis kurstaki HD-73 on S. frugiperda. The following method was used. Both bacterial strains were evaluated in vitro in 1 st instar S. frugiperda caterpillars, by means of histopathological assays. The Cry1Ab and Cry1Ac proteins, codified by the respective strains of B. thuringiensis, were evaluated in vivo by bioassays of 1 st instar S. frugiperda caterpillars in order to determine the Mean Lethal Concentration (LC 50 ). The results of the histopathological analysis of the midget of S. frugiperda caterpillars demonstrate that treatment with the B. thuringiensis thuringiensis strain was more efficient, because the degradations of the microvilosities started 9 hours after treatment application (HAT), while in the B. thuringiensis kurstaki the same effect was noticed only after 12 HAT. Toxicity data of the Cry1Ab and Cry1Ac proteins presented for the target-species LC 50 levels of 9.29 and 1.79 µg.cm , respectivamente. As cepas e proteínas sintetizadas por B. thuringiensis thuringiensis e B. thuringiensis kurstaki são eficientes no controle de S. frugiperda, e poderão ser usadas na produção de novos biopesticidas ou a utilização dos genes na transformação genética de Oryza sativa L. Histopatologia e efeito letal de cepas e proteínas Cry de Bacillus thuringiensis

Cry1Ab and Cry1Ac strains and proteins synthesized by Bacillus thuringiensis thuringiensis and B. thuringiensis kurstaki were assessed in the following phytopathogens: Rhizoctonia solani, Pyricularia grisea, Fusarium oxysporum and F. solani, which had their micelial growth decreased after incubation in the presence of the bacterial strains. As to Cry proteins, there were no inhibition halo development in the assessed concentrations.

Bioassays with insecticidal crystal proteins (ICPs) from Bacillus thuringiensis have demonstrated that Cry1Aa, Cry1Ac, and Cry1Ba are the most active toxins on larvae of the Anticarsia gemmatalis. The toxins Cry1Da and Cry1Ea are less toxic, and toxins Cry2Aa are not active. Binding of these ICPs to midgut sections of the A. gemmatalis larvae was studied using streptavidin-mediated detection. The observed staining patterns showed that Cry1Aa and Cry1Ac bound to the brush border throughout the whole length of the midgut. However, the binding sites of Cry1Ba were not evenly distributed in the midgut microvilli. The in vivo assays against larvae of 2nd instar A. gemmatalis confirmed the results from the in vitro binding studies. These binding data correspond well with the bioassay results, demonstrating a correlation between receptors binding and toxicity of the tested ICPs in this insect.