Herbivory by Boreioglycaspis melaleucae (Hemiptera: Psyllidae) Accelerates Foliar Senescence and Abscission in the Invasive Tree Melaleuca quinquenervia

WequantiÞed thedensity-dependent effects of herbivory by thepsyllidBoreioglycaspis 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 inßuenced 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 Þnally to light tan as they deteriorated. These changes in color, particularly theyellowing aspect,wereoftenmorepronounced along themain 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 inßuenced by leaf age or chemotype. Implications for biological control of M. quinquenervia are discussed.