Eficácia de fungos e nematoides entomopatogênicos testados isoladamente ou em combinação para controle de Rhipicephalus microplus: do laboratório para o campo

Abstract

Entomopathogenic fungi and nematodes are biocontrol agents widely investigated for the biological control of several pests, including ticks. This study aimed to determine the efficacy of fungi and nematodes, combined or not combined, against Rhipicephalus microplus engorged females under laboratory and field conditions. Bioassays under controlled conditions were conducted to evaluate the pathogenicity of the nematode Heterorhabditis bacteriophora HP88 against R. microplus females with different weights (150, 200, 250, 300, and 350 mg), and against females from eight different populations. In addition, a study under field conditions were conducted to evaluate the efficacy of H. bacteriophora HP88 formulated on Tenebrio molitor cadavers for controlling non-parasitic R. microplus on infested pastures. Likewise, a study was sought to determine, under controlled conditions, the synergistic combination between Metarhizium spp. and H. bacteriophora HP88 against R. microplus engorged females, as well as to determine a granular formulation containing M. robertsii IP 146 microsclerotia with potential to produce conidia when incubated onto different substrates. Lastly, a study was conducted to determine, under field conditions, the efficacy of combined granular formulation and H. bacteriophora HP88 infective juveniles (third stage) for controlling non-parasitic R. microplus population on infested pastures during different seasons of the year (wet or dry). Nematode pathogenicity to R. microplus females did not show variation of the percent control (98.4% to 97.5%) on the groups with different weights. There were also no differences on susceptibility of females from different populations (percent control between 89% and 99%) to HP88. In the field test, non-parasitic R. microplus population was reduced by 73.1% in the plots treated with H. bacteriophora HP88. Combined treatments with Metarhizium spp. and H. bacteriophora HP88 reduced biological parameters of engorged females, with additive effect detected. However, treatmented with M. robertsii IP 146 combined with H. bacteriophora HP88 sub-doses demonstrated synergism. The field test conducted in the wet season reduced the non-parasitic R. microplus population on infested pastures, with efficacy of 54.09% (fungus only), 38.11% (nematode only), and 46.72% (fungi and nematodes combined). In the dry period, only the fungal treatment reduced R. microplus population, with efficacy of 26.27%. We concluded that M. robertsii IP 146 and H. bacteriophora HP88 are promising agents for biological control of the non-parasitic phase of R. microplus, although the treatment efficacy had varied according to the wet or dry seasons.