Comparison of three larval bioassays to evaluate susceptibility of Rhipicephalus (Boophilus) microplus to amitraz
Related Experiment Video
Updated: May 3, 2026
Topical Application Bioassay to Quantify Insecticide Toxicity for Mosquitoes and Fruit Flies
Published on: January 19, 2022
Tânia Regina Bettin Santos1, Guilherme Marcondes Klafke2, Felipe Geraldo Pappen3
1Laboratório do Doenças Parasitárias, Departamento de Veterinária Preventiva, Faculdade de Veterinária, Universidade Federal de Pelotas - UFPel, Capão do LeãoRS, Brasil, Laboratório do Doenças Parasitárias, Departamento de Veterinária Preventiva, Faculdade de Veterinária, Universidade Federal de Pelotas - UFPel, Capão do Leão, RS, Brasil.
Abstract:
Field samples of Rhipicephalus (Boophilus) microplus from the state of Rio Grande do Sul, Brazil, were assessed using the following methods: larval packet test (LPT), larval immersion test (LIT) and syringe immersion test (SIT). The following parameters were determined for each population and for the Mozo susceptible reference strain: lethal concentration for 50% (LC50) with its 95% confidence interval (95% CI), regression line slope and resistance ratio (RR). Using the LPT, only one population was susceptible to amitraz, presenting a RR of 1.9. Using the same technique, the other populations presented RRs of between 92.9 and 3445.8 and were considered resistant. The LC50 of the Mozo strain calculated using the LPT, LIT and SIT was 2.9, 27.3, and 52.7 µg/mL, respectively. In general, a good fit to the probit statistical model was only achieved using the LPT. The results obtained in this study impair recommendations for using the LIT and SIT to diagnose amitraz resistance in R. (B.) microplus populations. Additional studies are required to improve the sensitivity of these tests in relation to the LPT.
