Attraction of the biocontrol agent, Galerucella placida Baly (Coleoptera: Chrysomelidae) to the leaf surface alkanes of the weed, Polygonum orientale L.

Extraction, thin layer chromatography, and gas chromatography-mass spectrometry of leaf surface waxes of Polygonum orientale L. (Polygonaceae) weed revealed 16, 19 and 15 n-alkanes between n-C15 and n-C33 in the young, mature and senescent leaves, respectively. In the young, mature and senescent leaves, the predominant alkanes were (heptacosane, nonacosane and nonacosane) were 11.92, 15.95 and 14.83 %, respectively. Heneicosane, dotriacontane and tritriacontane were absent in the young and senescent leaves, whilst eicosane was absent only in the senescent leaves. The role of cuticular alkanes to the female insect, Galerucella placida Baly (Coleoptera: Chrysomelidae) was evaluated in the Y-shaped glass tube olfactometer bioassay under laboratory conditions. The cuticular alkanes from the young, mature and senescent leaves, and the synthetic blends comparable to the cuticular alkanes of three types of leaves were attractive to G. placida at 4, 1-2 and 4 leaf equivalent alkanes, respectively. Females were attracted to the individual synthetic n-C15, n-C16, n-C17, n-C18, n-C20, n-C21, n-C23, n-C24, n-C25, n-C26, n-C28 and n-C31 alkanes at the minimum concentrations of 4, 2, 1, 20, 40, 2, 4, 8, 6, 14, 14 and 50 µg in a dose-dependent bioassay, respectively. A synthetic blend of 1.60, 0.86, 11.90, 17.79, 1.82, 1.54, 12.06, 6.60, 6.55 and 25.45 µg of n-C16, n-C17, n-C18, n-C20, n-C21, n-C23, n-C24, n-C26, n-C28 and n-C31, respectively, indicated highest attraction of the insect, and provide a basis in developing a lure to monitor field population.