Resistance to amitraz in cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) and sensibility to plant extracts and entomopathogenic fungi

Abstract

The cattle tick Rhipicephalus (Boophilus) microplus (Canestrini) is a hematophagous ectoparasite for which the main hosts are cattle living in regions located between the parallels 32ºN and 32ºS. The damages caused by the high infestation of the parasite are related to blood lost, leather damage and transmission of causative agents of babesiosis and anaplasmosis, with consequent reduction on the meet and milk production. The actual situation of the tick chemical control is characterized by the progressive increase in the number of cases of resistance for this ectoparasite, with consequent increase in the acaricide application frequency and the presence of pesticide residues in milk and meet. Amitraz, of formamidine group, has been used for more than 30 years as acaricide and presents an important role in the control of cattle tick. Its application is viable because of the short residual period and rapid degradation in the environment. The amitraz resistance in R. (B.) microplus has already been reported in many countries, based on adult female tests. There are cases of amitraz resistance reported in Brazil. The objective of this research is to study the resistance of R. (B.) microplus to amitraz and to study possible alternative procedures for the control of the pest, aiming at providing basic information for the management of the pest in Brazil. The specific objectives are: 1) to establish the lethal concentrations 50% and 99% (LC50 and LC99) for the diagnosis of amitraz resistance in R. (B.) microplus in larval immersion test (LIT), using "Mozo" susceptible strain; 2) to evaluate resistance in cattle ticks, from several farms in the State of São Paulo with suspect of amitraz resistance; 3) to submit a strain of R. (B.) microplus to amitraz selection pressure, to observe the potential for evolution of resistance and to obtain a strain resistant to the acaricide; 4) to conduct studies on the mechanisms of the acaricide resistance (tests with synergists); 5) to carry out tests of sensibility of R. (B.) microplus to some plant extracts; 6) to carry out tests of sensibility of R. (B.) microplus to some strains of entomopathogenic fungi.