Leaf age heterogeneity among selected Populus clones: 1 Influences on feeding and oviposition preferences of adult Chrysomela scripta F (Coleoptera: Chrysomelidae): 2 Correlations of preferences with foliar phenolic glycoside profiles

摘要

The cottonwood leaf beetle, Chrysomela scripta F., (Coleoptera: Chrysomelidae), is considered to be one of the more serious defoliators of plantation Populus in North America. This research was undertaken to examine the effects of leaf age and plant chemicals on the feeding and oviposition behaviors of adult beetles. The most preferred leaf age class was established for both behaviors and the composition and concentration of selected phenolic glycosides were analyzed for the most and least preferred leaf age classes. Correlations were then made between the phenolic glycoside profiles of the leaves and the host preferences of the beetles for both behaviors;Greenhouse preference studies performed under controlled conditions established that adults exhibit preferences among selected Populus for feeding and oviposition and that the same clones were favored choices for both behaviors. Preferences for specific leaf age classes were observed and the relationship between leaf age class and feeding damage can be explained by a quadratic model. A positive correlation was also found between the amount of feeding damage and the distribution of egg masses;Laboratory high performance liquid chromatography analyses were conducted to determine the concentrations of salicin, salicortin, and tremulacin in the foliage of a non-host aspen hybrid and the same Populus clones used in the preference trials. Two leaf age classes (the most preferred age class and a nonpreferred age class) were examined and most samples contained all three of the targeted chemicals. Overall, the concentrations were higher in the younger, most preferred leaves than in the nonpreferred leaves. No direct correlations between host selection for feeding and oviposition and the concentration of these glycosides were found, but some general trends were evident. The levels of salicin and salicortin were moderate to high in the most preferred clones, while the concentrations of tremulacin were low. This suggests possible positive influences of salicin and salicortin on host selection and possible negative effects of tremulacin. The degree of resistance exhibited by some Populus may be caused in part to the composition or concentration of phenolic glycosides, especially salicin.