Loss of in vitro Efficacy of Topical Commercial Acaricides on Rhipicephalus microplus (Ixodida: Ixodidae) From Antioquian Farms, Colombia.

ABSTRACT In Antioquia, the problems to control Rhipicephalus microplus (Canestrini, 1888) tick infestations have spread and ranchers claim conventional treatments are no longer effective. In this study, the in vitro efficacy of commercial topical products was tested with ticks obtained from two dairy farms in Antioquia with severe repeated infestations. About 800 engorged ticks were collected directly from animals in two separate visits at the beginning and end of the same month. The adult immersion test was used, which exposed groups of 40 ticks from each collection at the recommended concentration for five commercial products and combinations for 5 min. Efficacy was determined by comparing the reproductive index (fecundity × fertility) of each treated group to that of the control group. The values of all reproductive parameters obtained with ticks from the two collection dates were very similar. Cypermethrin (150 ppm) and amitraz (208 ppm) separately showed very low efficacies of only 10–20% at one farm...