Synergistic action of piperonyl butoxide with macrocyclic lactones in Rhipicephalus microplus

Area of Science:

• Veterinary Entomology
• Parasitology
• Chemical Ecology

Background:

• Rhipicephalus microplus resistance to macrocyclic lactones poses significant economic challenges in livestock production.
• Indiscriminate acaricide use drives resistance, necessitating novel control strategies like synergists.

Purpose of the Study:

• To evaluate piperonyl butoxide (PBO) as a synergist to overcome macrocyclic lactone resistance in Rhipicephalus microplus.
• To assess the impact of PBO on ivermectin, eprinomectin, and moxidectin efficacy in Brazilian tick populations.

Main Methods:

• Bioassays were conducted on five Rhipicephalus microplus populations from Northeast Brazil.
• The synergistic effect of PBO was tested in combination with ivermectin, eprinomectin, and moxidectin.
• Larval concentration-mortality (LC50) values were determined to quantify resistance and synergism.

Main Results:

• Widespread resistance to macrocyclic lactones was confirmed, with varying LC50 values across populations.
• PBO significantly enhanced acaricide efficacy, reducing LC50 values in multiple populations for all tested macrocyclic lactones.
• Synergism was observed even in highly resistant populations, particularly with eprinomectin and moxidectin.

Conclusions:

• Piperonyl butoxide (PBO) demonstrates significant synergistic activity, partially overcoming macrocyclic lactone resistance in Rhipicephalus microplus.
• Oxidative detoxification is implicated as a contributing mechanism to resistance, but other factors are also involved.
• PBO offers a promising pharmacological approach to improve acaricide effectiveness against resistant tick strains.