ABSTRACT Among the management and control tactics of the coffee berry borer Hypothenemus hampei (Ferrari), there is the use of entomopathogenic fungi. Due to the importance of prospecting isolates of entomopathogenic fungi for the control of the coffee berry borer, the objective of this study was to evaluate the efficiency of 26 isolates of entomopathogenic fungi in the control of this insect pest in the laboratory. The coffee berry borers were immersed in a solution adjusted to the concentration of 1 to 3 × 108 conidia/mL of each isolate and the control treatment (sterilized water). After seven days total mortality and confirmed mortality were evaluated. The isolates that caused the highest mortality and two commercial isolates were selected for evaluation of lethal concentration (LC50 and LC90) and lethal time (LT50 and LT90). Coffee berry borers were treated at different conidia concentrations for lethal concentration to assess total and confirmed mortality. For a lethal time, the coffee berry borers were treated at the concentration of 108 conidia/mL of the selected isolates, and, after two days and every 24 hours until the eighth day, the number of dead individuals was verified. Among the 26 isolates evaluated, 24 presented mortality higher than the control treatment, and three presented mortality higher than 85%. In the LC50 and LC90 assays, the IBCB 353 and IBCB 364 isolates were more lethal to H. hampei. In the LT50 and LT90 assays, the IBCB 66 and IBCB 353 isolates caused lethality in a shorter time.

RESUMO: O algodoeiro (Gossypium hirsutum) é acometido por várias doenças de importância econômica, dentre as quais a meloidoginose (Meloidogyne incognita raças 3 e 4). Entre os métodos de controle dessa doença, destacam-se as aplicações de nematicidas, a solarização, a aração profunda, a rotação de culturas e o uso de microrganismos antagonistas. Dentre as espécies do gênero Bacillus, existem estirpes que atuam como biorreguladores e antagonistas de vários patógenos. Os testes para identificação dessas estirpes são prejudicados pela dificuldade de se obter grandes populações do patógeno e pelo tempo de execução dos testes in vivo que devem ser conduzidos por cerca de 90 dias. Diante disso, o presente trabalho teve como objetivo comparar a toxicidade de estirpes de B. thuringiensis a dois nematoides, M. icognita e Caenorhabditis elegans, verificando a possibilidade de empregar C. elegans como indicador para a seleção de estirpes com potencial de biocontrole contra M. incognita. Para tanto, a toxicidade de nove estirpes de B. thuringiensis para C. elegans e M. incognita foi avaliada em laboratório e em casa de vegetação. A maioria das estirpes tóxicas ao C. elegans in vitro, também foi tóxica ao M. incognita, sendo que três delas (S906, S1192, S2036) reduziram significativamente as populações dos dois nematoides. O efeito tóxico apresentado pelas estirpes de B. thuringiensis contra C. elegans foram similares aos apresentados pelos mesmos isolados contra M. incognita in vivo. Esses resultados sugerem que é plausível o uso do C. elegans como indicador de toxicidade para seleção de estirpes de B. thuringiensis tóxicas a M. incognita.

ABSTRACT: The cotton plant (Gossypium hirsutum) is affected by several diseases of economic importance, among them root-knot nematode (Meloidogyne incognita races 3 and 4). Methods to control this disease include the application of nematicides, solarization, deep plowing, crop rotation and use of antagonistic microorganisms. Among species of Bacillus, there are strains that act as bioregulators and antagonists of several pathogens. Tests to identify these strains are hampered by the difficulty of obtaining large populations of the pathogen and by the time of execution of the in vivo tests that should be conducted for about 90 days. The objective of this research was to compare the toxicity of B. thuringiensis strains to two nematodes, M. incognita and Caenorhabditis elegans, evaluating the possibility of using C. elegans as an indicator for the selection of strains with biocontrol potential against M. incognita. Therefore, the toxicity of nine B. thuringiensis strains on C. elegans and M. incognita was evaluated under laboratory and greenhouse conditions. Most strains toxic to C. elegans in vitro were also toxic to M. incognita, and three of them (S906, S1192, S2036) significantly reduced the populations of the two nematodes. The toxic effect of B. thuringiensis strains on C. elegans was like that reported for the same bacterial isolates on M. incognita in vivo. These results suggested that it is plausible to use C. elegans as an indicator of toxicity for selection of B. thuringiensis strains toxic to M. incognita.

Neste trabalho foram realizados testes de patogenicidade com 210 estirpes de Bacillus thuringiensis contra larvas de Aedes aegypti e Culex quinquefasciatus, a fim de se determinar as mais eficazes. Estas estirpes foram isoladas de diversas regiões do Brasil e estão armazenadas na coleção de Bacillus spp. da Embrapa Recursos Genéticos e Biotecnologia. As estirpes selecionadas foram caracterizadas por métodos morfológicos (microscopia), bioquímicos (SDS-PAGE 10%) e moleculares (Reação em Cadeia da Polimerase). Foram selecionadas seis estirpes entomopatogênicas de Bacillus thuringiensis. Nenhuma das estirpes de Bacillus thuringiensis apresentou produtos de PCR esperados para a detecção dos genes cry4, cry11 e cyt1A. A patogenicidade das estirpes não está associada à presença das toxinas Cry4, Cry11 ou Cyt, assim, essas estirpes poderão ser utilizadas para a formatação de um bioinseticida alternativo contra mosquitos.

The objective of this work was to evaluate 210 Bacillus thuringiensis strains against Aedes aegypti and Culex quinquefasciatus larvae to select the most effective. These strains were isolated from different regions of Brazil and are stored in a Bacillus spp. collection at Embrapa Recursos Genéticos e Biotecnologia, Brasília, Brazil. The selected strains were characterized by morphological (microscopy), biochemical (SDS-PAGE 10%) and molecular (PCR) methods. Six B. thuringiensis strains were identified as mosquito-toxic after the selective bioassays. None of the strains produced the expected PCR products for detection of cry4, cry11 and cyt1A genes. These results indicate that the activity of mosquitocidal Brazilian strains are not related with Cry4, Cry11 or Cyt proteins, so they could be used as an alternative bioinsecticide against mosquitoes.