Attraction of the Biocontrol Agent, Galerucella placida Towards Volatile Blends of Two Polygonaceae Weeds, Rumex dentatus and Polygonum glabrum.

The Polygonaceae weed, Rumex dentatus L. grows in association with wheat, mustard and potato, while Polygonum glabrum Willd. grows in association with rice in India. Both larvae and adults of Galerucella placida Baly (Coleoptera: Chrysomelidae) voraciously consume these weeds. Applications of synthetic herbicides to control weeds are harmful to the environment including beneficial organisms. We propose to find volatile organic compounds (VOCs) from both weeds causing attraction of the biocontrol agent, G. placida, in order to attempt to use the insect as a biological weed control. Behavioral responses of G. placida towards volatile blends characteristic of undamaged (UD), insect-damaged (ID), jasmonic acid-treated (JA) or mechanically-damaged (MD) plants were conducted by Y-tube olfactometer bioassays. Cuminaldehyde was predominant in VOCs of UD R. dentatus, ID P. glabrum, and both JA and MD R. dentatus and P. glabrum. Geraniol was predominant in VOCs of UD P. glabrum, while 1,3-diethylbenzene predominated in VOCs of ID R. dentatus. Females were more attracted towards volatile blends of ID plants compared to UD or JA plants. Females did not show attraction towards volatile blends of JA plants. We identified two bioactive synthetics blends, one comprised of seven compounds - 16.65 µg 1,3-diethylbenzene, 10.72 µg acetophenone, 6.52 µg 2,6-(E,Z)-nonadienal, 2.46 µg 1-nonanol, 4.19 µg decanal, 9.86 µg 4-ethylacetophenone and 3.34 µg 1-hexadecene dissolved in 25 µl CH2Cl2 and the other containing five compounds - 2.50 µg 2-octanol, 6.84 µg limonene, 0.64 µg dodecane, 6.63 µg 4-ethylacetophenone and 0.24 µg geranyl acetone dissolved in 25 µl CH2Cl2. These two blends of volatile compounds could be used to attract the biocontrol agent during early vegetative period of these two weeds, which could lead to eradication of weeds from crop fields.