Nematóides entomopatogênicos (Rhabditida, Heterorhabditidae) no controle biológico de Rhipicephalus (Boophilus) microplus (Acari, Ixodidae)

Abstract

Because of the widespread resistance of cattle ticks to commercial carrapaticides and the need to protect the environment and food supply from chemical residues, there is increasing interest in finding new control alternatives. Among these is the use of entomopathogenic nematodes as biological control agents. In this effort, the Embrapa Dairy Cattle Research Center (Embrapa Gado de Leite) has been conducting a line of research investigating the interactions between cattle ticks and these nematodes. The present work examines the efficiency of two nematode species in the control of cattle ticks. We conducted three experiments to evaluate the in vitro potential of Heterorhabditis bacteriophora HP88 and Heterorhabditis amazonensis RSC-5 as biological controls of Rhipicephalus (Boophilus) microplus. The study was conducted in the Parasitology Laboratory of Embrapa Gado de Leite in Juiz de Fora, Minas Gerais, Brazil. In the first experiment the efficiency was evaluated of different concentrations of infective juveniles of H. bacteriophora HP88 to control the ticks. The efficiency of the treatment was greater than 90% at all the concentrations tested, demonstrating this isolate is highly effective in reducing the reproductive capacity of R. (B.) microplus in laboratory conditions. In the second experiment, the same evaluation was carried out employing different concentrations of the nematode H. amazonensis RSC-5. The results were inferior to those obtained with H. bacteriophora HP88. The best efficacy xvi was 67% in the treatment with 300 EPNs/female. Because it was more efficient, we chose H. bacteriophora HP88 for the third experiment, which evaluated the effect of different exposure times of engorged females of R. (B.) microplus to infective juveniles of this nematode. The results obtained show that exposure times shorter than 24 hours are not sufficient for the nematode to have a significant control effect on this tick. However, with exposure for longer than 24 h the control percentage rose to 82%, and at 48 and 72h it reached 100%. The results obtained in this study show that in vitro these nematodes are efficient in controlling cattle ticks, but further studies are necessary to investigate the of these biological control agents under field conditions and the possible impacts this can cause.