Fumigant toxicity of cassia bark and cassia and cinnamon oil compounds to Dermatophagoides farinae and Dermatophagoides pteronyssinus (Acari: Pyroglyphidae).

The toxicity to adults of the American house dust mite, Dermatophagoides farinae, and the European house dust mite, Dermatophagoides pteronyssinus, of cassia bark and cassia and cinnamon oil compounds was examined using residual contact and vapour-phase toxicity bioassays. Results were compared with those of the currently used acaricides: benzyl benzoate and dibutyl phthalate. The acaricidal principles of cassia bark were identified as (E)-cinnamaldehyde and salicylaldehyde. In fabric-circle residual contact bioassays with adult D. farinae, salicylaldehyde (17.3 mg/m(2)) and (E)-cinnamaldehyde (25.8 mg/m(2)) were 2.5 and 1.7 times more toxic than benzyl benzoate (43.7 mg/m(2)), respectively, based on 24-h LD(50) values. The acaricidal activity was more pronounced in benzaldehyde, menthol, alpha-terpineol, and thymol (70.8-234.3 mg/m(2)) than in dibutyl phthalate (281.0 mg/m(2)). Against adult D. pteronyssinus, salicylaldehyde (17.3 mg/m(2)) and (E)-cinnamaldehyde (19.3 mg/m(2)) were 2.4- and 2.2-fold more active than benzyl benzoate (41.9 mg/m(2)). The toxicity of benzaldehyde, menthol, alpha-terpineol, and thymol (75.3-179.2 mg/m(2)) was higher than that of dibutyl phthalate (285.1 mg/m(2)). In vapour-phase toxicity tests with adult D. farinae, the test compounds described were much more effective in closed--but not in open--containers, indicating that the effect of these compounds was largely a result of action in the vapour phase.