Acaricidal activity of Cnidium officinale rhizome-derived butylidenephthalide against Tyrophagus putrescentiae (Acari: Acaridae).

The acaricidal activity of materials derived from the rhizome of Cnidium officinale Makino against Tyrophagus putrescentiae Schrank adults was examined using direct contact application and fumigation methods, and compared with that of benzyl benzoate and N,N-diethyl-m-toluamide (DEET). The biologically active constituent of the Cnidium rhizome was identified as butylidenephthalide by spectroscopic analyses. On the basis of 24-h LD50 values, acaricidal activity was more pronounced with butylidenephthalide (5.80 microg cm(-2)) than with benzyl benzoate (9.75 microg cm(-2)) and DEET (16.26 microg cm(-2)). In typical poisoning symptoms, butylidenephthalide resulted in lethargy of treated mites, leading to death without knockdown, whereas benzyl benzoate and DEET caused death associated with uncoordinated behaviour. In a fumigation test with T. putrescentiae adults, butylidenephthalide was much more effective in closed containers than in open ones, indicating that the effects of this compound were largely due to action in the vapour phase. Naturally occurring C. officinale rhizome-derived materials merit further study as potential T. putrescentiae control agents or as lead compounds.