Host-associated Genetic Differentiation of the Green Citrus Aphid, Aphis spiraecola (Hemiptera: Aphididae) in Algeria
The green citrus aphid, Aphis spiraecola Patch, is an important pest attacking many plant species, including citrus. We have analyzed the genetic variability among green citrus aphid adults sampled from six citrus cultivars grown in Algeria (an orange, a grapefruit, a lemon and three mandarin cultivars), using the random-amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) technique. Analysis of molecular variance (AMOVA), based on RAPD markers, indicated a significant difference between the studied samples, correlated to the host plant species, while host cultivar and geographical origin had no significant impact on the genetic diversity. Two-dimensional PCO analysis confirmed AMOVA results, showing the grouping of the different insects into four major clusters according to their host plant species. The Neighbor-Joining dendrogram constructed based on the Euclidian distance grouped the accessions into four main clusters according to their host plant species genotypes, giving insight into the coevolution of insect strains with their corresponding citrus species. In order to investigate any possible relationship between the genetic aggregation of insect genotypes and the leaf morphology in citrus species, we carried out leaf morphological characterization and surveyed the degree of infestation of the studied citrus cultivars. Leaves of grapefruit and orange were the most similar morphologically and the most attacked by aphids, suggesting that genetically close biotypes would be compatible with these two species. Results of this study are a step toward the development of an integrated controlling strategy against A. spiraecola in North Africa, taking into account the host specialization that seems to play a key role in shaping the genetic diversity of A. spiraecola.