Caracterização e seleção de isolados de Beauveria bassiana para o controle microbiano do carrapato Boophilus microplus / Characterization and selection of Beauveria bassiana isolates to microbiological control of Boophilus microplus tick

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Beauveria bassiana is an entomopathogenic fungus used worldwide as a biological control agent of pest arthropods. The present study aimed at characterizing several isolates of B. bassiana and selects those with major potential to control ticks population and other arthropods under natural conditions. Thus, 53 isolates of B. bassiana and 7 isolates including 5 other Beauveria spp. and 1 Engyodontium albus (=Beauveria alba) were investigated. These isolates were originally from different regions of Brazil and other nations, and different hosts or substrate. Initially, all the isolates were morphologically analyzed and investigated about the potential of conidial production. Afterwards, experiments were conducted to investigate the genetic diversity of Brazilian isolates of B. bassiana, to evaluate the spatial distribution of genotypes, and to understand the genetic relationship among isolates of different species of Beauveria. Thus, all isolates were analyzed by isozymes electrophoresis, AFLP-PCR and sequencing of ITS1 and ITS2 regions. The results have permitted the taxonomic identification of isolates and the selection of those with major potential to conidial production. The results have also showed the detection of high genetic variability among B. bassiana isolates, indicating that this fungus represents a species aggregate. Furthermore, the genetic distance among isolates was directly related to the geographic distances. In addition, the isolates were evaluated to UV-B tolerance, heat tolerance, and cold activity. Heat and cold are two abiotic factors of the environment that restrict the use of entomopathogenic fungi as agents for biological control of insects. In addition, solar radiation, particularly the UV-B wavelength, is a major environmental factor that can negatively affect this entomopathogenic fungus in the field. High variability in UV-B tolerance was detected among the isolates after 2 h of radiation exposure. Conidial relative germination ranged from 0% to almost 80%, and a delayed germination was detected. Moreover, isolates of B. bassiana originating from lower latitudes tended to have lower UV-B tolerance than isolates from higher latitudes. A high variability in thermotolerance was also observed among the isolates after 2 h of heat exposure at 45 C, ranging from low, to medium, to high viability. The thermal death point of most resistant isolates was between 44 C and 45 C after 6 h of heat exposure. At cold temperatures most of the isolates grew at 5 C. An attempt to correlate the latitude of origin with thermotolerance or cold activity indicated that isolates from higher latitudes were more cold-active than isolates from nearer the equator. The present study also evaluated the virulence of the isolates toward Boophilus microplus larvae, and virulence ranged from very low to very high. It was observed that different populations of B. microplus may present different susceptibility to B. bassiana infection. Therefore, the present study has selected isolates of this entomopathogenic fungus with major effective potential to control B. microplus and other pest arthropods under environmental conditions.

ASSUNTO(S)

beauveria spp boophilus microplus medicina veterinaria biological control controle biológico

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