Neiva Knaak

Mode of Action and Specificity of Bacillus thuringiensis Toxins in the Control of Caterpillars and Stink Bugs in Soybean Culture

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.

Toxic effects of essential plant oils in adult Sitophilus oryzae (Linnaeus) (Coleoptera, Curculionidae)

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.

Histopathology of Anticarsia gemmatalis Hübner (Lepidoptera; Noctuidae) treated with Nucleopolyhedrovirus and Bacillus thuringiensis serovar kurstaki

The Anticarsia gemmatalis is responsible for the use of chemical insecticides in the soybean culture, causing a significant increase in the costs of farming and a great unbalance in the ecosystem. The use of microbial agents, like Bacillus thuringiensis serovar kurstaki (Btk) and Anticarsia gemmatalis nucleopolyhedrovirus (AgNPV), they are an alternative to chemical control of the pest insects. In the interaction analysis of the entomopathogenic bacteria and virus it is considered important the in vitro action mode of these microbiology control agents. Therefore, the present study aims the histopathological analysis of the A. gemmatalis larvae digestive system after the interaction in vivo of the entomopathogenic Btk and AgNPV, represented the Dipel and Baculovirus anticarsia formulations, respectively. The evaluations were realized in larvae of 2nd instar, in which the mortality was evaluated daily, and a histopathology was done with collected larvae in time of 1, 3, 6, 12 and 24 hours after the treatments application. The results of the in vivo assays reveal that the treatment using the association of AgNPV-Btk (98.68% of mortality) was more efficient than using AgNPV isolatedly (81.28% of mortality), but the Btk when used isolatedly had a mortality of 100%. The treatments showed significant (P<0.05) differences between AgNPV and Btk, AgNPV and AgNPV/Btk. The histopathological analysis of the AgNPV and Btk in A. gemmatalis larvae suggests that the Dipel and Baculovirus anticarsia products were more efficient when they were used simultaneously, because the action of AgNPV was intensified when used in association with Btk, causing changes in the larvae midgut after 6 hours of treatments. When the entomopathogens were used isolating the gut cells alterations were observed only 12 hours after the treatments.

In vitro effect of Bacillus thuringiensis strains and Cry proteins in phytopathogenic fungi of paddy rice-field

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.

Potential of essential plant oils to control insects and microorganisms

As substâncias repelentes ou atraentes das plantas sao, principalmente, de natureza terpenica e se apresentam como moleculas de baixo peso molecular e volatil. Essas substâncias, normalmente, sao conhecidas como aromaticas e se denominam oleos essenciais, os quais se acumulam em todos os orgaos vegetais. Nos vegetais, os oleos essenciais desenvolvem funcoes relacionadas com sua volatilidade, agindo na atracao de polinizadores, na protecao contra predadores, nos patogenos, na perda de agua, no aumento de temperatura e tambem desempenhando funcoes ecologicas, especialmente como inibidoras de germinacao. Essas caracteristicas tornam as plantas que os produzem poderosas fontes de agentes biocidas, o que e largamente estudado nos agroecossistemas, principalmente no que concerne as acoes bactericida, fungicida e inseticida. Os oleos essenciais tem como principais constituintes os monoterpenos, seguidos pelos sesquiterpenos, alem de compostos aromaticos de baixo peso molecular. Sua funcao especifica na planta ainda e desconhecida, porem se acredita que, durante o seu desenvolvimento, as plantas superiores sintetizam terpenoides essenciais para o proprio crescimento. Essas substâncias do metabolismo secundario podem agir como inibidores de germinacao, protecao contra predadores, atracao de polinizadores, entre outras. Entretanto, a avaliacao desses compostos com finalidades diversas, como, por exemplo, no controle de microrganismos patogenicos de plantas cultivadas ou, ainda, como inseticida ou herbicida natural, e recente, visto que sao poucos os trabalhos de pesquisa desenvolvidos e publicados nessa area. Esta revisao em artigo trata das interacoes dos oleos essenciais de plantas medicinais, silvestres e cultivadas com microrganismos e insetos. Palavras-chave: oleos essenciais, insetos, fungos, bacterias.

Histopathology and the lethal effect of Cry proteins and strains of Bacillus thuringiensis Berliner in Spodoptera frugiperda J.E. Smith Caterpillars (Lepidoptera, Noctuidae)

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 1st 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 1st instar S. frugiperda caterpillars in order to determine the Mean Lethal Concentration (LC50). 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 LC50 levels of 9.29 and 1.79 microgxcm-2 respectively. The strains and proteins synthesised by B. thuringiensis thuringiensis and B. thuringiensis kurstaki are effective in controlling S. frugiperda, and may be used to produce new biopesticides or the genes may be utilised in the genetic transformation of Oryza sativa L.

Receptors and Lethal Effect of Bacillus thuringiensis Insecticidal Crystal Proteins to the Anticarsia gemmatalis (Lepidoptera, Noctuidae).

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.

Microbial Diversity: Relevance and Relationship Between Environmental Conservation And Human Health

This work presents bibliographic data on the role and function of microbial diversity. The increasing use of probiotics and prebiotics foods has led to the studies on their actual functions in the human body. It is known that in the environment, microorganisms are extremely important in recycling of nutrients, balance of trophic chains, vital physiological activities in the plants and animals, as well as the conservation of natural habitats. In human food, these microscopic organisms contribute from flavoring products to the synthesis of antimicrobial substances and vitamins essential to living beings.

Bacteria-Soil-Plant Interaction: This Relationship to Generate can Inputs and New Products for the Food Industry

A thorough study of microbial communities that inhabit aquatic agro-ecosystems is crucial to a better understanding of what happens in the soil, since these microorganisms play important roles for the maintenance of the habitat. Irrigated rice culture is very common in Brazil. However, the incorrect use of these environments can affect the soil and cause damage. The bacteria-soil-plant interaction has been used in order to support biotechnology, as the rhizosphere possesses a different microbial ecology from the rest of the soil. Microorganisms from this region are directly related to plant growth. Bacterial diversity in soil is extremely diverse, with its population changed rapidly as new nutrients are made available or the existing ones are exhausted. The bacteria that live there receive both the plant nutrients and antimicrobial agents, which are selective and inhibit certain undesirable microorganisms. Aiming at this data, this article has an objective to review existing literature on the interaction between microorganisms and their relationship with the plants, which can be transmitted to food through minerals and/or enzymes, thus enabling the generation of inputs or new products.

Toxicology of the Bioinsecticides Used in Agricultural Food Production

As populations grow in numbers, the demands for food production increase and are generally met by the intensification of livestock breeding and the increase of agricultural activities. This in turn increases the quantity of chemical pesticides required to control the losses in production caused by insect pests preying on the food plants and disturbing the animals. Once applied these pesticides may cause resistance to the synthetic molecules, contaminate biotic and abiotic components like plants, soil, water and/or the local water network and can also effect non-targeted organisms, such as fish, small mammals, birds and so on.