Comparative acaricidal properties of different solvents and surfactants on Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Abstract

Use of herbal acaricides is considered one of the options for integrated tick management. Many natural compounds have low water solubility and use of solvents/surfactants is obligatory to test the efficacy of the herbal extracts in experimental conditions. In an attempt to identify best suitable solvents, experiments were conducted on laboratory reared homogenous colonies of adults of R.(B.) microplus. Adult immersion test was conducted by exposing the adults on solvents (methanol, ethanol, acetone, n-butanol, di-methyl sulphoxide) and surfactant (tween 20). The effect of solvents and surfactant was monitored in terms of causing mortality and inhibition of oviposition (IO). Out of 4 solvents used, n-butanol was found most toxic to tick system with a mean mortality of 20.0±8.2% at 10% concentration. Though no mortality was seen in 25% ethanol treated ticks but percentage inhibition of oviposition (%IO) of 10.3 was recorded. In contrast, upto 50% concentration acetone and methanol were found to be safe as a solvent since it had least toxic effect on tick mortality. Amongst the two detergents tested up to 6% concentration tween- 20 found safe while DMSO can be used even at higher concentration up to 10% without any toxic effect. The results revealed that of the 4 commonly used solvents tested, acetone was the least toxic while n-butanol was highly toxic to ticks both in terms of causing mortality and IO. The surfactant DMSO was found safe at 10% level against adults of R.