Isolation of Insecticidal Constituents from the Essential Oil of Ageratum houstonianum Mill. against Liposcelis bostrychophila Badonnel

The aim of this research was to determine chemical composition and insecticidal activities of the essential oil of Ageratum houstonianum Mill. aerial parts against booklice, Liposcelis bostrychophila Badonnel, and to isolate any insecticidal constituents from the oil. Essential oil of A. houstonianum was obtained by hydrodistillation and analyzed by GC-MS. A total of 35 components in the essential oil were identified. The major compounds were precocene II (62.68%), precocene I (13.21%), and β-caryophyllene (7.92%). Based on bioactivity-guided fractionation, precocene II and precocene I were isolated and identified as the active constituents. The essential oil exhibited contact toxicity against L. bostrychophila with an LC50 value of 50.8 g/cm2. Precocene II (LC50 = 30.4 g/cm2) exhibited stronger acute toxicity than precocene I (LC50 = 64.0 g/cm2) against the booklice. The essential oil and the two isolated constituents also possessed strong repellent activity against L. bostrychophila. The results indicated that the essential oil and its constituent compounds have potential for development into natural insecticides or repellents for control of insects in stored grains.