Acaricidal activity of the plant sesquiterpenoids α-costic acid and inuloxin A against the cattle ectoparasitic tick, Rhipicephalus (Boophilus) annulatus

The obligate ectoparasite Rhipicephalus (Boophilus) annulatus, also known as cattle tick, is the hard tick vector of babesiosis, a protozoal infection that causes severe meat production losses at huge economic costs. Although babesiosis was eradicated from the United States, its vector still exists in Mexico and different security measures are used to prevent its reintroduction into the U.S. Furthermore, the massive use of chemical acaricides during the last century has resulted in the development of resistance and toxicological problems. A possible and more sustainable alternative could be represented by the applications of biopesticides. Recently, two sesquiterpenoids, inuloxin A and alpha-costic acid isolated fromDittrichia viscosa, a perennial native plant of the Mediterranean basin, showed several interesting biological activities including acaricidal and antifeedant activities. Both inuloxin A and alpha-costic acid caused an impact on the hatch rate of the eggs and a larval mortality rate higher than 80% in vitro bioassays on eggs of R. annulatus. Moreover, the hatch rate of the eggs and the mortality rate of the larvae seem to be dependent on the timing of application of the compounds on the eggs. These results suggested a potential use of both compounds to control R. annulatus. [GRAPHICS] .