Effects of rootstock and flushing on the incidence of three insects on 'Clementine de Nules' citrus trees.

We evaluated the influence of six different citrus rootstocks on the incidence of the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), and the aphid species, Aphis gossypii Glover and A. spiraecola Patch (Hemiptera: Aphididae), on 'Clementine de Nules' trees (Citrus clementina Hort. ex Tan.). Sampling was conducted during 2005 and 2006 in a grove of 3-yr-old trees in southern Spain with six rootstocks arranged in a completely randomized block design. Incidence (i.e., degree of infestation) and availability of resources for herbivores were assessed bi-weekly, and in addition, a "flushing index" was estimated as the number of young shoots (as a percentage of total shoots) susceptible to herbivore injury. Our results showed that contrasting factors affected the incidence of populations of P. citrella, A. gossypii, and A. spiraecola on 'Clementine de Nules'. Incidence of P. citrella was significantly dependent on the flushing pattern observed throughout the study, whereas the reverse was true for the aphid species. Among these, A. spiraecola had similar levels of incidence regardless of rootstock, whereas A. gossypii were found almost exclusively on leaves of 'Clementine de Nules' grafted on 'Cleopatra mandarin' (Citrus reshni Hort. ex Tan). Potential implications of these results on pest control are discussed.