Sown ground cover in pear orchards influences the abundance of key predators with variable results on pest control depending on the species

Abstract Enhancing ground cover vegetation may favour biological pest control. This research aimed to test the effect of cover management on the abundance of natural enemies and pest control in pear orchards. Two types of cover management (i.e., sown/mown cover) were tested in an organic pear orchard during three years in southern Spain. The cover and pear trees were sampled periodically between April and June to estimate the abundance of arthropods. The abundance of all the groups of natural enemies, including ants, spiders, predatory thrips, hemipterans and four families of parasitoids, as well as phytophagous insects such as aphids and psyllids, was significantly higher in the vegetation of the sown than in the mown cover. The sown cover was found to significantly reduce the abundance of aphids on pear trees, while it had a neutral effect on Cacopsylla pyri . This reduction in aphid numbers could be mainly attributed to the increase in the abundance of spiders and predatory mirids on the trees with the sown cover. In contrast, the sown cover was found to significantly reduce the abundance of the ant Lasius grandis on pear trees in relation to the mown cover. Overall, the management of the cover had a stronger effect on the assemblage of arthropods on the understory vegetation than on pear trees. The increase of the abundance of natural enemies on pear trees with the sown cover could have been due to their movement from the cover and/or the reduction of harassment due to the lower ant activity.