WHY IT MATTERS WHERE ON A LEAF A FOLIVORE FEEDS

Because the tip of many dicot leaves matures and ceases expansion well before the base, we predicted that the removal of a given amount of leaf tissue from the base of an expanding leaf would result in greater reductions in final leaf area and overall plant performance than removal of the same amount of tissue from the tip of an expanding leaf or from either the base or tip of mature, fully expanded leaves. We tested this notion by removing a circular 3.9 cm(2) hole from either the base or tip of rapidly expanding leaves (20-30% expanded, two nodes from the apex) or nearly fully expanded, mature leaves (85-100% expanded, five nodes from the apex) of tobacco (Nicotiana tabaccum) and measuring the final area of the hole, the final area of the fully expanded damaged leaf, and the number and mass of fruits produced by a plant. A given amount of area removed from the base of an expanding leaf resulted in almost 4 times the amount of visible damage than occurred when the same amount of damage was applied to the tip or base of a mature leaf and over twice the amount of visible damage than occurred on the tip of an expanding leaf. Furthermore, damage to the base of an expanding leaf resulted in nearly a 40% reduction in the final area that the leaf would have achieved without damage and a 35% reduction in the number and mass of fruits produced. These results not only suggest that where on a leaf a folivore feeds has consequences to the ultimate area that a leaf can reach and to overall plant performance, but they also have strong implications for a number of research areas in plant-herbivore interactions. For example, these data show that a lack of consideration of leaf developmental patterns can result in gross overestimates of consumption by folivores and severe under-estimates of the effect of folivory on leaf area display.