Relationship between poplar leaf chemicals and cottonwood leaf beetle adult feeding preferences

Lin, Sisi
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The cottonwood leaf beetle, Chrysomela scripta F. (Coleoptera: Chrysomelidae), is considered to be one of the most serious defoliators of Populus plantations in North America. This research was conducted to understand the relationship between poplar leaf secondary chemicals and adult beetle feeding preferences;Leaf surface chemicals from a cottonwood leaf beetle-preferred poplar clone, 'Eugenei' (Populus deltoides x Populus nigra), was found to induce feeding in the adult cottonwood leaf beetle. The feeding stimulants were isolated and identified as n-beheryl alcohol (C22), n-lignoceryl alcohol (C24), n-hexacosanol (C26), n-octacosanol (C28), n-triacontanol (C30), and [alpha]-tocopherylquinone ([alpha]-TQ), (2-(3-hydroxy-3,7,11,15-tetramethyl-hexadecyl)-3,5,6-trimethyl-<1,4>benzoquinone). It is the first time that long chain fatty alcohols and [alpha]-TQ have been identified as cottonwood leaf beetle adult feeding stimulants. And it is the first time that [alpha]-TQ has been reported as a feeding stimulant for an insect. Fatty alcohols or [alpha]-TQ alone do not induce beetle feeding significantly, but a mixture of alcohols and [alpha]-TQ synergistically stimulates beetle feeding;Field-planted University of Washington poplar pedigree materials (parent clones ILL-129, Populus deltoides, and 93-968, Populus trichocarpa, F, clones, 53-242 and 53-246, and 87 F2 selections) were used for leaf disc feeding tests. Field cage feeding tests were performed with parent and F1 clones. Leaf surface chemicals, long chain fatty alcohols and [alpha]-TQ, and the phenolic glycosides tremulacin and salicortin were analyzed to correlate chemical abundance with cottonwood leaf beetle adult feeding preference. The beetles showed varied feeding preferences among parent clones, F1 clones, and F2 clones. Contents of the alcohols or the phenolic glucosides did not explain adult beetle feeding preference. Content of [alpha]-TQ on the leaf surface, in the presence of the alcohols, could explain the adult beetle feeding preference. The beetle preferred to feed on clones with [alpha]-TQ rather than on clones without [alpha]-TQ. As the amount of [alpha]-TQ increased, the feeding preference increased, and then decreased as the amount of [alpha]-TQ increased further.