Susceptibility of field populations of Haematobia irritans to fipronil in Uruguay

Abstract

Fipronil was registered in Uruguay in 1997, and, since then, it has been used for the control of Haematobia irritans irritans and Rhipicephalus microplus. The susceptibility of H. irritants to this drug has not been evaluated. Therefore, the goal of the present study was to evaluate the resistance of H. irritans to fipronil. Additionally, a survey was carried out with the farmers to evaluate the use of fipronil for H. irritans control in the ranches where the flies came from. For the bioassays, 31 field populations of H. irritans were exposed to 10 concentrations of fipronil (3.2-16.0μg.cm2), and their LC50 values were calculated using probit analysis. A bioassay was performed with horn flies from the susceptible colony maintained at the USDA-ARS Knipling-Bushland U.S. Livestock Insects Research Laboratory for comparison and calculation of resistance ratios (RRs). All 31 field populations surveyed in the study were susceptible to fipronil, with resistance ratios ranging from <0.5 to 2.2. Four populations with RRs >1 did not differ significantly from the susceptible strain. A single population showed an RR >2.2. Overall, the survey shows that fipronil was mostly used for R. microplus control, and in only three ranches, which were free of R. microplus, was fipronil used for horn fly control. Seventeen farmers did not use fipronil at all in the last three years. It is concluded that, in Uruguay, field populations of horn flies remain susceptible to fipronil.

Phenotypic and Target-Directed Screening Yields New Acaricidal Alternatives for the Control of Ticks

“…South American countries are the main producers and suppliers of beef internationally [1]; Brazil is the world's leading exporter of beef, with 200 million heads, and breeding which has increased approximately 30% in the last decade [2]; therefore, any event that damages livestock production in these countries is of high importance and has an economic impact [3,4]. The tick Rhipicephalus microplus (R. microplus) is one of the main ectoparasites of cattle, generating economic losses in Uruguay of USD 46 million annually, due to production losses, treatments costs, and deaths due to tick-borne diseases [2]. R. microplus is a vector of multiple hemoparasites such as Babesia bovis, B. bigemina, and Anaplasma marginale, causative agents of tick-borne diseases.…”