Toxicity of hiba oil constituents and spray formulations to American house dust mites and copra mites.

Abstract

Dermatophagoides farinae and Tyrophagus putrescentiae are recognised as an important source of allergens. An assessment was made of the toxicity of hiba, Thujopsis dolabrata var. hondai, oil and 13 organic compounds and the control efficacy of four experimental spray formulations containing the oil (5-30 g L(-1) spray) against both mite species. In a contact + fumigant mortality bioassay, (-)-thujopsene was the most toxic constituent against D. farinae and T. putrescentiae (24 h LC50 9.82 and 10.92 µg cm(-2)), and the toxicity of the compound was nearly identical to that of benzyl benzoate (9.33 and 10.14 µg cm(-2)). The toxicity was more pronounced in carvacrol, (+)-terpinen-4-ol, β-thujaplicin, (-)-terpinen-4-ol, cedrol and α-terpineol (LC50 12.05-15.20 and 12.74-16.48 µg cm(-2)) than in N,N-diethyl-3-methylbenzamide (LC50 35.53 and 38.42 µg cm(-2)) against both mite species. The hiba oil 30 g L(-1) spray and commercial permethrin (cis:trans 25:75) 2.5 g L(-1) spray treatment resulted in 100 and 11% mortality against the two mite species respectively. In vapour-phase mortality tests, the two compounds were consistently more toxic in closed versus open containers, indicating that toxicity was achieved mainly through the action of vapour. Reasonable mite control in indoor environments can be achieved by a spray formulation containing the 30 g L(-1) hiba oil as a potential contact-action fumigant.