Occurrence of oak leaf phylloxeran aphid, Phylloxera quercina (Ferr.) on Quercus brantii in Lorestan province, western Iran

Aphids are one of the most important agricultural and forest pests that may directly injure by sucking the sap of plant organs and indirectly by the transmission of microbial pathogen agents into the plant hosts. Moreover, other indirect forms of damage from feeding may be seen as gall formation, deformation of plant organs, chlorosis / necrosis spotting of the leaves all three due to the injection of poisonous saliva, and the presence of sooty mold view resulting in the honeydew excretion as a food source for the saprophytic fungi. The number of aphids is currently more than 5200 species, of which about 69 species within six genera belong to the family Phylloxeridae. Apart from the grape Phylloxera, a commercial pest of grapevines worldwide, the habitats of remaining species are forest trees and non-agroecosystems. The oak leaf phylloxeran aphids have a complex life cycle as exclusively egg-laying with parthenogenic forms. These aphids overwinter as egg inside seams and shell gaps of small branches or sometimes as first nymphal instar in branches. This study aimed to identify an aphid species feeding of Brant's oak, Quercus brantii, as a probable cause of yellow chlorosis spotting on the leaves of infected trees. Various methods have been proposed to assign unknown specimens to known species using their DNA barcodes.

Aphid specimens were collected on Q. brantii oak trees in eight selected forest sites around Khorramabad County, Lorestan Province. They were identified based on molecular and morphological evidences and was subjected to molecular characterization. DNA sequencing of partial COI gene fragment was performed, and the phylogeny of this species was compared with other species within the genus Phylloxera. In order to identify, the mounted aphid samples (microscopic slides) were morphologically identified by the conventional method under a light microscope with the help of taxonomical keys. 

Samples were recognized as Phylloxera quercina (Ferrari, 1872) based on molecular and morphological identification. The phylogenetic tree was constructed as a fully resolved tree with Phylloxera genus as monophyly, dichotomous branching, and near-full bootstrap values.

The present study is the first report showing the occurrence of P. quercina as a pest in the Zagros vegetation zone. Here we suggest the annual monitor of seedling oak and investigation of the geographical distribution of pest species. The utility of COI barcode gene fragment, along with the morphological characters, can help accurately identify Phylloxera species in Iran.