Insecticidal activity of isolated phenylpropanoids from <i>Alpinia galanga</i> rhizomes against <i>Spodoptera litura</i>

Abstract

Botanical insecticides as a means of controlling insects present an alternative approach that is safer than the use of synthetic insecticides. The present study identified the insecticidal activity of extracts of the rhizomes of <i>Alpinia galanga</i> (L.) Willd. and seven isolated phenylpropanoids against the second instar of <i>Spodoptera litura</i> Fab. by topical application. The ethyl acetate extract had the highest toxicity on this insect with LD₅₀ values of 1.68 and 1.25 μg/larva after 24 and 48 h posttreatment, respectively. Among the seven phenylpropanoids separated from the ethyl acetate extract, 1'<i>S</i>-1'-acetoxychavicol acetate was identified as the most active compound with LD₅₀ values of 1.63 and 1.40 μg/larva after 24 and 48 h posttreatment, respectively, followed by <i>p</i>-coumaryl diacetate. In addition, the two active compounds decreased glutathione <i>S</i>-transferase activity and increased acetylcholinesterase activity. <i>p</i>-Coumaryl diacetate also decreased carboxylesterase activity.