Contact Toxicity of an Essential Oil from Acorus calamus (Acoraceae) Rhizomes against Tetranychus urticae and Tetranychus macfarlanei (Acari: Tetranychidae) and Amblyseius longispinosus (Acari: Phytoseiidae)1

The contact toxicity activity of an essential oil extracted from Acorus calamus (L.) (Acoraceae) was evaluated against the phytophagous spider mites Tetranychus urticae Koch and Tetranychus macfarlanei Baker & Pritchard (Acari: Tetranychidae) and the predatory mite Amblyseius longispinosus (Evans) (Acari: Phytoseiidae). Adult mortality 24 h following application of 5% (v/v) concentration of the essential oil exceeded 90% for T. urticae and T. macfarlanei. Application of 1.2–5% concentrations of the essential oil to mite eggs reduced egg viability, with 0–54% hatch of T. urticae eggs and 0% hatch of T. macfarlanei eggs 6 d following treatment. At 2.5%, the essential oil was toxic to A. longipinosus by residual contact toxicity (58% mortality) and direct contact toxicity (0% mortality). No eggs and 47.6 eggs of A. longispinosus were oviposited with residual contact toxicity and direct contact toxicity, respectively. The chemical constituents of the essential oil, as determined with gas chromatography–mass spectrometry, showed that camphor (41.07%) and 5,5-dimethyl-2-ethynylcyclopent-2-en-1-ol (27.96%) were the major chemical compounds of the essential oil. These results indicate that this essential oil extracted from fresh A. calamus rhizomes could prove useful in controlling T. urticae and T. macfarlanei. Our findings also showed that the essential oil had no deleterious effects against A. longispinosus by direct contact toxicity test; however, A. longispinosus consuming spider mite eggs treated with essential oil were negatively impacted.