Identification and virulence of metarhizium anisopliae (Hypocreales: Clavicipitaceae) as biological control agent of rhipicephalus microplus (acari: Ixodidae) in Panama

Abstract

The Rhipicephalus microplus tick is the main ectoparasite of cattle in Panama and other tropical and subtropical regions of the world. Traditionally, the R. microplus control method is based on the use of chemical acaricides. However, this method has obstacles such as the development of resistance, contamination of the environment, and food, which has favored the evaluation of control strategies alternative to acaricides. The objective of this study was to identify and evaluate the virulence of native isolates of Metarhizium aniso-pliae on larvae of R. microplus under in vitro conditions. The identification of Mt1, Mt2, and Mt5 isolates was performed based on their morphological characteristics and by sequencing the ITS-5.8S region of ribosomal DNA. The three native isolates were identified as M. anisopliae. Bioassays were done using a completely randomized experimental design. With each isolate, four concentrations of 1x105, 106, 107 and 108 conidia mL–1, and a control (0.1% Tween 80 solution) were evaluated. Significant differences (P < 0.01) were found in the mortality percentages (PM) on larvae between the concentrations evaluated for each of the isolates, at 10, 20, and 30 days post-treatment (DPT). The three isolates reached the maximum PM (>98%) on larvae at concentrations 1x107 and 1x108 conidia mL–1, at 30 DPT. In the control treatment, no larval mortality was observed. The Mt5 isolate was the most virulent with a mean lethal concentration (LC50) of 1.17x105 conidia mL–1, followed by the Mt2 and Mt1 isolates with LC50 of 2.94x105 and 1.23x106 conidia mL–1, respectively. The results found in the present study suggest that the native Mt5 and Mt2 isolates of M. anisopliae could be considered promising agents for the biological control of the tropical tick of the R. microplus cattle in cattle farms in Panama.