Evaluación de la resistencia de Rhipicephalus spp. a ivermectina y factores condicionantes en bovinos en el cantón Joya de los Sachas.

Abstract

The tick genus (Rhipicephalus spp) is distributed throughout the world causing economic losses in livestock farms in tropical and subtropical areas. Acaricides play an important role in the control of these populations; howerer the excessive use is a consequence for resistance. The objective of the current research work was to evaluate the resistance of Rhipicephalus spp to ivermectin and conditioning factors in cattle. In the field, 880 ticks were collected from 4 farms and conducted a survey. In the laboratory, resistance to ivermectin was evaluated by means of bioassays. For the adult immersion test (AIT), it determined: fertility index, oviposition inhibition, reproductive efficiency, product efficacy and the percentage of the resistance through Kolmogorov-Smirnov normality tests, two-way analysis of variance (ANOVA) and comparision of means by Dunnett. For the larval immersion test (LIT) determined mortality, also carried out a PROBIT analysis in order to calculate the lethal concentrations CL50, CL99 and slope, afterwards for the conditioning factors performed a Pearson correlation with the resistance ratio values. On the other hand, the resistance levels in the PIA were: 62.5 percent susceptible, 27.8 percent medium resistance and 16.7 percent high resistance in tick populations. The LIT determined the resistance ratio CL50 ranging between 1.0 and 7.00 and CL99 between 1.0 and 6.15 among the farms, presenting susceptibility in 75 percent of the farms, a correlation was found between the application interval and the presence of resistance. Finally, it is concluded that Rhipicephalus spp. populations are widely susceptible to ivermectin; being the application interval of the acaricidal a conditioning factor associated to resistance.