title: Effects of passages through a suitable host of the fungus, Metarhizium anisopliae, on the virulence of acaricide-susceptible and resistant strains of the tick, Rhipicephalus microplus.
abstract: The aim of this work was to assess the virulence of strain M379 of the fungus, Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) after different passages through a suitable host and at different concentrations for the control of both acaricide-susceptible and resistant strains of the tick, Rhipicephalus (formerly Boophilus) microplus Canestrini (Ixodida:Ixodidae) in vitro. The highest value of LC50 for the susceptible strain corresponded to zero passage with 7.68 × 107 conidia/ml followed by the fourth passage with 2.68 × 107, which reduced 2.87-fold the lethal concentration. When comparing LC50 values of the fourth vs. the seventh passage (2.59 × 105 conidia/ml), the lethal concentration was reduced 103.47-fold by the seventh passage. In addition, in the resistant strain the LC50 highest value corresponded to zero passage with 4.95 × 107 conidia/ml followed by the fourth passage with 7.86 × 106, which reduced 6.30-fold the lethal concentration. When comparing LC50 values of the fourth vs. the seventh passage (1.04 × 105 conidia/ml) in the resistant strain, the lethal concentration was reduced 75.58-fold by the seventh passage. These results suggest that the number of passages on M. anisopliae through a suitable host increased its virulence on both R. microplus strains. When comparing LC50 of the zero passage through a suitable host of both acaricide-susceptible and resistant strains, the highest LC50 values corresponded to the susceptible strain with 7.68 × 107 conidia/ml followed by the resistant one with 4.95 × 107, showing that on the resistant strain the lethal concentration is reduced by 1.55-fold. When comparing the fourth passage, the highest values of LC50 corresponded to the susceptible strain with 2.68 x 107 conidia/ml followed by the resistant one with 7.86 × 106 conidia/ml, showing for the resistant strain a 3.41-fold reduced lethal concentration. Moreover, when comparing the seventh passages, the highest values of LC50 corresponded to the susceptible strain with 2.59 × 105 followed by the resistant with 1.04 × 105 conidia/ml, revealing for the resistant strain a 2.49-fold reduced lethal concentration. These results suggest that the resistant strain needs a lower concentration of conidia than the susceptible strain. In this case, the acaricide-resistant strain is more susceptible to M. anisopliae of zero- and seven-passage strains.
authors.affiliation: 1CeIB, Universidad Autónoma del Estado de Morelos. Av. Universidad 1001, Colonia Chamilpa, Cuernavaca, Morelos, Mexico, C.P. 62209, Mexico.
authors.forename: Markis
authors.initials: M
authors.lastname: Adames
authors.forename: Manuel
authors.initials: M
authors.lastname: Fernández-Ruvalcaba
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Peña-Chora
authors.forename: Víctor M
authors.initials: VM
authors.lastname: Hernández-Velázquez
mesh_terms: D000818:Animals; D002417:Cattle / Q000469:parasitology; D054884:Host-Pathogen Interactions; D052981:Metarhizium / Q000472:pathogenicity* / Q000502:physiology; D008800:Mexico; D010058:Oviposition; D010572:Pest Control, Biological / Q000379:methods*; D048494:Rhipicephalus / Q000382:microbiology*; D013172:Spores, Fungal; D013983:Tick Control / Q000379:methods; D014774:Virulence