Residual and Direct Contact Toxicities of Crude Extracts and Essential Oils from Acorus calamus L. (Acoraceae) Rhizomes against Cassava Red Mites (Acari: Tetranychidae)

Abstract

Abstract Tetranychus truncatus Ehara (Acari: Tetranychidae) is a serious economic pest of many plants in Thailand and other countries. The use of plant extracts is an alternative to conventional synthetic pesticides for controlling mite pests. This study was conducted to evaluate the residual and direct contact toxicities of crude extracts and essential oils obtained from Acorus calamus L. (Acoraceae) rhizomes against T. truncatus eggs and adult females under laboratory conditions. Residual toxicity was assayed by applying compounds on leaf discs and then releasing adult female mites on the discs; direct contact toxicity was assayed by spraying the compounds on eggs and adult females. In residual assays, a 10% (v/v) concentration of essential oils extracted from fresh A. calamus rhizomes caused 73.8% mortality of T. truncatus adults, while treatment with oils from dried rhizomes caused 91.8% mortality of adults. In direct-contact toxicity assays, essential oils from fresh rhizomes reduced egg hatch by 96.3% at 5% (v/v) concentration and 100.0% at 10%. Oils extracted from dried rhizomes reduced egg hatch by 28.8% at 5% and 91.8% at 10%. The respective median lethal concentrations (LC50s) were 2.18% and 5.91%, based on cumulative mortality at 7 d after treatment. Methylene chloride extracts from fresh and dried rhizomes (individual extraction method) caused a cumulative adult mite mortality of 100% and 91.4% at 5% (v/v) concentration, with LC50s of 1.31% and 2.52%. Based upon our results, essential oils and methylene chloride extracts from A. calamus rhizomes appear as suitable botanical acaricides for further development for the management of T. truncatus.