In Vivo and in Vitro Evaluation of Permethrin, Cypermethrin or Zeta-Cypermethrin Mixed with Plant Extracts against Susceptible and Resistant (San Alfonso) Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Strains

Acaricide resistance is a major problem that hinders the control of the cattle tick Rhipicephalus (Boophilus) microplus in Mexico. Permethrin (P), cypermethrin (C) and zeta-cypermethrin (Z) have been used to control R. (B.) microplus, and tick populations have developed resistance to these acaricides. The aim of the present study was to evaluate the effectiveness of a mixture containing P, C, or Z mixed with plant extracts through in vitro laboratory bioassays, using susceptible and triple resistant (San Alfonso) R. microplus strains. Untreated controls received only water. Results of laboratory bioassays using larval packet tests revealed an efficacy of 100% (P), 100% (Z), and 98.03% (C) using susceptible larvae, and an efficacy of 88.67% (P), 91.51% (C), and 99.27% (Z) on triple-resistant larvae. Egg laying, larvae hatching and efficacy was assessed using ticks collected from treated and untreated animals. Product Z produced a 92.04% efficacy on engorged ticks collected from experimentally-infested cattle, whereas C and P exerted 80.66% and 20.04% efficacy, respectively. Engorged females collected exclusively from control animals were challenged in vitro with the experimental products, and efficacy was as follows: 91.37% (Z), 85.95% (C), and 13.58% (P). Adding plant extracts to a pyrethroid formulation led to dramatic increases of percent reduction of both susceptible and resistant immature ticks in contrast to untreated larvae and susceptible adults. Results from this study may lead to suggesting the adoption of an acari-cide-botanical mixture strategy for tick control worldwide.