Persistência de Bacillus thuringiensis Berliner, 1911 em condições de campo na cultura da soja (Glycine max (l.) merrill) e efeito na mortalidade de Anticarsia gemmatalis (Hübner, 1818) (Lepidoptera: Erebidae)
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Data
2019-07-24
Autores
Nascimento, Joacir do
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Universidade Estadual Paulista (Unesp)
Resumo
A soja se destaca com um dos principais produtos do agronegócio brasileiro. No entanto, o ataque de insetos desfolhadores como Anticarsia gemmatalis comprometem a produtividade. O controle dessa praga é baseado na aplicação de inseticidas químicos e no uso de plantas Bt. Contudo, a seleção de populações resistentes é uma séria limitação para o manejo dessa praga. Em vista disso, torna-se necessário um sistema de manejo que também auxilie a retardar a evolução da resistência. Uma alternativa é o uso de agentes de controle microbiano, com o uso de bioinseticidas à base da bactéria Bacillus thuringiensis (Bt). Entretanto, a principal limitação do uso desses bioinseticidas é elevada sensibilidade a fatores climáticos, como radiação UV, temperatura e umidade. A maioria dos estudos disponíveis sobre persistência de Bt são antigos e foram realizados no hemisfério Norte em espécies ornamentais e florestais, onde as condições climáticas diferem do hemisfério Sul. Os bioinseticidas a base de Bt são utilizados em todo o mundo, visando o controle de pragas agrícolas. Dentre as suas principais vantagens em relação aos inseticidas convencionais se destacam a seletividade aos inimigos naturais e risco reduzido ao meio ambiente. Apesar de algumas limitações, esses bioinseticidas foram muito importantes para suprimir surtos recentes de lepidópteros praga no Brasil, onde os inseticidas convencionais falharam. Diante disso, faz-se necessário estudos de persistência em condições de campo. Os ensaios de persistência de Bt em campo foram conduzidos na cultura da soja nas safras 2017 e 2018 na área experimental da FCAV/UNESP, com parcelas de 10m x 5m e 4 repetições. Os tratamentos utilizados foram conduzidos em esquema fatorial [(2x3x3x2)+1], constituídos de cepas de B. thuringiensis subsp. tolworthi HD-125 (2017) e B. thuringiensis subsp. kurstaki HD-1 (2018) sem e com encapsulamento nos respectivos anos e do bioinseticida Dipel composto de dois horários de aplicação (8:00 e 16:00 horas), três espectros de gota (fina, média e grossa), duas vazões de aplicação (70 e 100 L.ha-1). Água foi utilizada como controle. E os ensaios de mortalidade de A. gemmatalis foram realizados no LCMAP/FCAV. A concentração de Bt na calda para aplicação foi 3 x 108 esporos.mL-1. Doze horas após a aplicação dos tratamentos, foram realizadas oito (primeira safra) e cinco (segunda safra), devido a 55 mm de precipitação a segunda safra foi realizado somente 5 coletas de folhas no terço superior das cinco linhas centrais de cada parcela, com um intervalo de 12 horas entre as coletas, totalizando 30 folhas. Para cada folha foram retirados 2 discos de 3,0 cm de diâmetro; um utilizado no bioensaios de mortalidade de A. gemmatalis e outro para avaliar a persistência do Bt através da contagem de esporos. No teste de mortalidade, foram utilizadas 25 lagartas por tratamento, distribuídas em 5 repetições. A avaliação da mortalidade foi realizada 5 dias após a montagem do bioensaio. Na avaliação da persistência, foi realizada a contagem de esporos utilizando câmara de Neubauer e microscópio com contraste de fase (400 x). O bioensaio de mortalidade demonstrou que não houve diferença estatística quando utilizado gota grossa na aplicação, bem como quando avaliado o horário de aplicação. A formulação encapsulada utilizada não influenciou na persistência do Bt e na mortalidade de A. gemmatalis
The soybean stands out as one of the main products of Brazilian agribusiness. However the attack of defoliating insects such as Anticarsia gemmatalis compromises productivity. Control of this pest is based on the application of chemical insecticides and the use of Bt plants. However, the selection of resistant populations is a serious limitation for the management of this pest. Given this, a management system that also helps to retard the evolution of resistance becomes necessary. An alternative is the use of microbial control agents with the use of Bacillus thuringiensis (Bt) -based Biopesticide. However, the main limitation of the use of these bioinsecticides is their high sensitivity to climatic factors such as UV radiation, temperature, and humidity. Most of the available studies on Bt persistence are old and have been carried out in the northern hemisphere on ornamental and forest species, where climatic conditions differ from the southern hemisphere. Bt B. thuringiensisbased Bioinsecticides are used worldwide to agricultural pest control. Among its main advantages over conventional insecticides are selectivity to natural enemies and reduced risk to the environment. Despite some limitations, these bioinsecticides have been very important in suppressing recent outbreaks of pest Lepidoptera in Brazil, where conventional insecticides have failed. Therefore, persistence studies under field conditions are necessary. Field Bt persistence tests were conducted on soybean crop in 2017 and 2018 crops in the experimental area of FCAV / UNESP, with plots of 10m x 5m and 4 replications. The treatments were conducted in a factorial scheme [(2x3x3x2) +1], consisting of strains of B. thuringiensis subsp. tolworthi HD-125 (2017) and B. thuringiensis subsp. kurstaki HD-1 (2018) without and with encapsulation in the respective years and the Dipel® bioinsecticide composed of two application times (8:00 and 16:00 hours), three drop spectra (fine, medium and coarse), two application rates (70 and 100 L.ha-1). Water was used as a control. And A. gemmatalis mortality assays were performed on the LCMAP / FCAV. The concentration of Bt in the spray solution was 3 x 108 spores.mL-1 . Twelve hours after the application of the treatments, eight (first crop) and five (second crop) leaf collections were performed in the upper third of the five central lines of each plot, with an interval of 12 hours between collections, totaling 30 leaves. For each sheet, 2 3.0 cm diameter discs were removed; one used in A. gemmatalis mortality bioassays and the other to evaluate the persistence of Bt by spore counting. In the mortality test, 25 caterpillars per treatment were used, distributed in 5 repetitions. Mortality assessment was performed 5 days after bioassay assembly. Spore counting was performed using a Neubauer chamber and phasecontrast microscope (400 x) to evaluate Bt persistence. The mortality bioassay showed that there was no statistical difference when coarse drop was used in the application, as well as when evaluate for application times The encapsulated formulation used did not influence Bt persistence andmortality of A. gemmatalis.
The soybean stands out as one of the main products of Brazilian agribusiness. However the attack of defoliating insects such as Anticarsia gemmatalis compromises productivity. Control of this pest is based on the application of chemical insecticides and the use of Bt plants. However, the selection of resistant populations is a serious limitation for the management of this pest. Given this, a management system that also helps to retard the evolution of resistance becomes necessary. An alternative is the use of microbial control agents with the use of Bacillus thuringiensis (Bt) -based Biopesticide. However, the main limitation of the use of these bioinsecticides is their high sensitivity to climatic factors such as UV radiation, temperature, and humidity. Most of the available studies on Bt persistence are old and have been carried out in the northern hemisphere on ornamental and forest species, where climatic conditions differ from the southern hemisphere. Bt B. thuringiensisbased Bioinsecticides are used worldwide to agricultural pest control. Among its main advantages over conventional insecticides are selectivity to natural enemies and reduced risk to the environment. Despite some limitations, these bioinsecticides have been very important in suppressing recent outbreaks of pest Lepidoptera in Brazil, where conventional insecticides have failed. Therefore, persistence studies under field conditions are necessary. Field Bt persistence tests were conducted on soybean crop in 2017 and 2018 crops in the experimental area of FCAV / UNESP, with plots of 10m x 5m and 4 replications. The treatments were conducted in a factorial scheme [(2x3x3x2) +1], consisting of strains of B. thuringiensis subsp. tolworthi HD-125 (2017) and B. thuringiensis subsp. kurstaki HD-1 (2018) without and with encapsulation in the respective years and the Dipel® bioinsecticide composed of two application times (8:00 and 16:00 hours), three drop spectra (fine, medium and coarse), two application rates (70 and 100 L.ha-1). Water was used as a control. And A. gemmatalis mortality assays were performed on the LCMAP / FCAV. The concentration of Bt in the spray solution was 3 x 108 spores.mL-1 . Twelve hours after the application of the treatments, eight (first crop) and five (second crop) leaf collections were performed in the upper third of the five central lines of each plot, with an interval of 12 hours between collections, totaling 30 leaves. For each sheet, 2 3.0 cm diameter discs were removed; one used in A. gemmatalis mortality bioassays and the other to evaluate the persistence of Bt by spore counting. In the mortality test, 25 caterpillars per treatment were used, distributed in 5 repetitions. Mortality assessment was performed 5 days after bioassay assembly. Spore counting was performed using a Neubauer chamber and phasecontrast microscope (400 x) to evaluate Bt persistence. The mortality bioassay showed that there was no statistical difference when coarse drop was used in the application, as well as when evaluate for application times The encapsulated formulation used did not influence Bt persistence andmortality of A. gemmatalis.
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Glycine max, Inseto, Microorganismo, Pragas agrícolas, Insect, Crop pest, Microorganism