We quantified the density-dependent effects of herbivory by the psyllid Boreioglycaspis melaleucae Moore on the senescence of expanding and fully expanded leaves from two chemical variants (chemotypes) of the invasive tree Melaleuca quinquenervia (Cav.) S. T. Blake. Foliar chlorophyll content (OD) and percent nitrogen were not influenced by leaf age classes and chemotypes. In contrast, increases in the level of herbivory resulted in concomitant decreases in chlorophyll compared with undamaged leaves, with medium and high levels of herbivory reducing chlorophyll content by 64 and 72%, respectively. Likewise, low, medium, and high levels of herbivory resulted in 20, 53, and 60% reductions in percent nitrogen, respectively. Color analysis showed that increased herbivory also increased the amount of damaged tissue per leaf across both age classes, but younger leaves showed less susceptibility to herbivory than older leaves. Leaves sustaining moderate to high levels of herbivory progressed from dark green to yellow and finally to light tan as they deteriorated. These changes in color, particularly the yellowing aspect, were often more pronounced along the main leaf veins and vascular tissues. Feeding by B. melaleucae increased the likelihood of leaf abscission by 4.7-fold compared with leaves not subjected to herbivory and was not influenced by leaf age or chemotype. Implications for biological control of M. quinquenervia are discussed.
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