Virulence of Mexican isolates of entomopathogenic fungi (Hypocreales: Clavicipitaceae) upon Rhipicephalus = Boophilus microplus (Acari: Ixodidae) larvae and the efficacy of conidia formulations to reduce larval tick density under field conditions

Authors

César Andrés Ángel-Sahagún, Universidad de GuanajuatoFollow
Roberto Lezama-Gutiérrez, Universidad de ColimaFollow
Jaime Molina-Ochoa, Universidad de ColimaFollow
A. Pescador-Rubio, Universidad de ColimaFollow
S. R. Skoda, USDA-ARSFollow
C. Cruz-Vázquez, Instituto Tecnológico El Llano Aguascalientes
A. G. Lorenzoni, University of Arkansas, Fayetteville
E. Galindo-Velasco, Universidad de ColimaFollow
H. Fragoso-Sánchez, SENASICA-SAGARPA
John E. Foster, University of Nebraska-LincolnFollow

ORCID IDs

John E. Foster

Document Type

Article

Date of this Version

2010

Citation

Veterinary Parasitology 170 (2010), pp. 278–286.

Comments

U.S. government work.

Abstract

The first objective was laboratory evaluation of the virulence of 53 Mexican isolates of fungi against larvae of Rhipicephalus (Boophilus) microplus. Thirty-three isolates of Metarhizium anisopliae var. anisopliae (Metschnickoff) Sorokin (Hypocreales: Clavicipitaceae) and 20 isolates of Isaria (Paecilomyces) fumosorosea (fumosoroseus) (Wize) (Eurotiales: Trichomaceae) were tested on 7-day-old larvae under laboratory conditions. Larvae were immersed in a suspension containing 10⁸ conidia/mL and the CL₅₀ values were estimated. Then, field tests were conducted to determine the efficacy of formulations of the isolate with the highest virulence. M. anisopliae (Ma 14 isolate) was formulated with four carriers: Tween, Celite, wheat bran, and Citroline (mineral oil) and applied on pasture beds of Cynodon plectostachyus (L.), at a dose of 2×10⁹ CFU/m². In the first trial, M. anisopliae was applied on plots naturally infested with larvae; in the second trial, tick populations in the experimental plots were eliminated and then re-infested with 20,000 7-day-old larvae. In the laboratory, all M. anisopliae isolates infected larvae with a mortality range between 2 and 100%; also, 13 of 20 I. fumosorosea isolates caused mortality rates between 7 and 94%. In the first field trial, 14 days post-application, conidial formulations in Celite and wheat bran caused 67.8 and 94.2% population reduction, respectively. In the second trial, the Tween formulation caused the highest larval reduction, reaching up to 61% (28 days post-application). Wheat bran formulation caused 58.3% larval reduction (21 days post-application) and was one of the most effective. The carriers and emulsifiers have a large impact on the effectiveness of conidial formulations.