Role of hedgerows and ground cover management on arthropod populations in pear orchards

With the failure of conventional chemical control against the pear tree psyllid Cacopsylla pyri (L.) (Homoptera: Psyllidae), strategies have been developed to enhance natural arthropod enemies of this pest. Modifying the vegetation adjacent to pear orchards is one integrated pest management (IPM) practice that can increase the agroecosystem plant diversity, thus favoring a natural balance between pest arthropods and their enemies. Different plant species were examined as sources of beneficial arthropods for the pear orchard. Arthropod faunas were sampled in the pear tree (Pyrus communis L.) canopy, the ground cover, and in the hedgerow tree species surrounding the orchard. Inter-relationships between pear and hedgerow tree species were studied by Spearman's rank correlation. Ash trees and ivy display a diversified fauna that was correlated with the pear tree community, but not with each other, Their influence on pear tree fauna is different: ash trees host specific psyllids and gall midges (Diptera: Cecidomyiidae), providing food for beneficial pear arthropods and ivy acts as a shelter species for beneficial pear arthropods. Calculation of correlations between the faunas of non-crop and crop plant species appears as a useful tool for estimating the risk (correlation between phytophagous guilds) and benefit (correlation between beneficial guilds) of plants dedicated to environmental crop management. The following orchard ground covers were tested: (1) bare ground; (2) natural grass cover; and (3) sown ground cover. Multivariate analysis was performed to characterize ground cover arthropod communities. Natural ground cover and sown ground cover sheltered distinct arthropod communities; the natural ground cover beneficial fauna was characterized by spiders and the sown ground cover fauna was characterized by ants. The structure and numbers of the arthropod assemblages collected on pear trees from the three types of ground management were different. The main beneficial arthropods on pear tree were Anthocoridae (Heteroptera) and Miridae (Heteroptera) in the sown area; Empididae (Diptera) and Miridae in the natural ground cover area; and Forficulidae (Dermaptera) and Miridae in the bare ground area. Moreover, the sown ground cover favored a higher beneficial : phytophagous ratio to that in the pear tree canopy. These results imply that interactions are likely to occur between pear trees and hedgerow, and between pear trees and ground cover within the orchard agroecosystem. Manipulating beneficial arthropods through vegetal environment management using selected tree and grass species shows promise in optimizing pear orchard IPM. (C) 1999 Published by Elsevier Science B.V. All rights reserved.