Population studies of arthropods on Melia azedarach in Seville (Spain), with special reference to Eutetranychus orientalis (Acari: Tetranychidae) and its natural enemies

Abstract

Eutetranychus orientalis has become an important pest of the ornamental tree Melia azedarach in the city of Seville (Spain). Trees suffer total defoliation at the end of summer. Studies were conducted in a regular plantation of this tree in the Miraflores Park in 2008 and 2009, to determine the arthropod faunal composition, with particular interest in the possible natural enemies of E. orientalis. Eutetranychus orientalis accounted for 98.3% of the arthropods found on the leaflets. Two species of phytoseiids were found, Euseius scutalis and Euseius stipulatus, but they only represented 0.2% of the arthropods. The most abundant insect was the predator thrips Scolothrips longicornis, which accounted for 0.9% of the arthropods found. The population of E. orientalis reached two peaks in 2008, with 325 individuals per leaflet in August, and 100 individuals per leaflet in November. Scolothrips longicornis densities closely followed E. orientalis, and predation was observed on various mite instars. Phytoseiids did not show such a response to the E. orientalis densities. Eutetranychus orientalis was more abundant in the exterior part of the plantation. No differences of arthropod densities were found between the various orientations in the plantation (north vs. south, east vs. west), although E. orientalis densities were different between rows. Distribution of E. orientalis population was highly aggregative, that of S. longicornis population was less aggregative, whereas the phytoseiid population showed a random distribution.