Abstract Stemona plants have been traditionally used against various insects in Thailand
and Southeast Asian countries. The acaricidal efficacy of 9 species of Stemona grown in
Thailand was evaluated against dairy cattle tick, Rhipicephalus microplus using adult
immersion test and in vivo evaluation on infested calves. From the ten Stemona root
extracts used in this study, S. collinsiae of a concentration 250 mg/ml possessed the
highest activity. In vivo study revealed that S. collinsiae extract could significantly reduce
the attached ticks on calf skin compared to the control and promoted not significantly
different efficacy from flumethrin, a common pyrethroid used in dairy farms. No side effect
was found on calves during the experiment. The results confirmed traditional use of
S. collinsiae as a better source of insecticide than other species and could be used as
guidance for further development of S. collinsiae as a herbal acaricide.