Selection of Filamentous Fungi for the Biocontrol of Rhipicephalus (Boophilus) Microplus in Tropical Regions

Abstract

Rhipicephalus microplus is an ectoparasite that causes significant losses to livestock due to spoliation of cattle and the high cost of current control techniques. The control of this parasite is chemically accomplished, but the incorrect use of this method is causing resistance in this species. An alternative to control would be the use of fungi, as they do not need to be ingested by the host, being only necessary to have contact with the target such that it can grow and colonize. Thus, the present study aimed to isolate, identify and select efficient fungal strains in the biological control of Rhipicephalus microplus in tropical weather, such as found in Brazil. Soil and Brachiaria brizantha forage samplings were carried out for isolation, quantification and identification of fungal species. Engaged females of R. microplus were collected for the bioassay of colonization rate, hatchability of eggs and production of mycotoxins. A total of 2x10 -3 CFU g -1 fungi were found and five genera were identified. Aspergillus spp. was the most frequent genus amidst the isolates obtained from both environments. The forage presented a greater amount of fungal colonies.g -1 when compared to the soil. We identified entomopathogenic, saprophytic, pathogenic and keratinophilic species with biotechnological potential as well as for use for biological control. Aspergillus was the most prevalent genus in both soil and forage of tropical regions. Elevated fungal variety was observed in the ecosystems we studied. Metarhizium anisopliae efficiently colonized the parasites in an 80% rate, and differed from other treatments (p< 0.01). These study open doors for investigations concerning the evaluation of other fungi colony counting's, forms of manipulation and other bioassays.Keywords: Dairy cattle; Tick; Biological control; In vitro tests; Microbiology; R. microplus; Rhipicephalus microplus; Aspergillus IntroductionTicks are ectoparasites characterized mainly by blood feeding, independently of family, genus or species [1], and the species Rhipicephalus microplus causes substantial losses for beef and milk cattle due to spoliation of cattle and the high cost of current control techniques [2][3][4]. These parasites have a lifecycle in the host and another in the pasture, and only females fill with blood, after they release themselves from the host and fall to the ground, where they seek a dark and humid place, suitable to lay their eggs [5]. The weather conditions in Brazil contribute to the development of the ectoparasite, allowing ticks populations to be virtually established in the entire country [6]. The chemical control is currently the preferred for the combat of ticks; however, the incorrect use of this method favors the occurrence of multiple or cross resistance [7,8]. In addition, the permanence of residues in animals and their products, thereby, alternatives to the control of this parasite are highly relevant [9].There are several natural enemies that contribute to the control of this parasite in the host or in the soi...