Complex architecture of Tamarix nilotica and resource utilization by the spindle-gall moth Amblypalpis olivierella (Lepidoptera: Gelechiidae).

Tamarix nilotica and the spindle-gall moth, Amblypalpis olivierella Rag., were studied to test the hypothesis that gall-inducing larvae utilize the most vigorous plant modules available on individual host plants. Five trees were studied in the vicinity of Caesarea, Israel, and the complexity of their architecture and phenology described. Four types of shoot were recognized: pendulous, upright, short, and bole sprouts. Three phenological conditions of shoot growth were categorized: ( 1 ) active meristematic growth; ( 2 ) dormant shoots; and ( 3 ) short shoots, which were particularly young and actively growing. The general response of gall initiation in relation to shoot-length classes per tree was unique for each tree, depending upon the frequency of the different shoot types available as resources. Only vigorously growing shoots were utilized by larvae, which invaded shoots just behind active meristems. Young Tamarix with mainly upright and active shoots supported an exponentially rising attack rate with increasing shoot-length class. Large mature trees with more heterogeneous architecture and shoot types illustrated gall patterns in relation to shootlength categories that were significant or not significant depending on shoot type, but attack was invariably concentrated on meristematically active shoots in the tree canopies. Where very vigorous basal sprouts were present, in pruned trees in landscaping, these were attacked at a low frequency. Thus, the plant vigor hypothesis is supported if examined in relation to the meristematic activity of shoots at the time of attack, but simpler patterns in relation to shootlength classes, observed so frequently in north temperate systems, are obscured by the architectural complexity of these Mediterranean climate trees. INTRODUCTION For small herbivores the host plant provides both food and habitat. Therefore, the way the plant grows is of central concern in understanding the plant-herbivore interaction. Plants, being modular organisms composed of populations of similar parts such as Author to whom correspondence should be addressed. E-mail peter.price@nau.edu