Effect of Different Cover Crops on the Presence of Arthropods in an Organic Apple (Malus domestica Borkh) Orchard

In the development of a sustainable agriculture, especially in fruit production, cover crops can contribute in two ways: 1) by improving soil fertility through the incorporation and retention of nutrients and water; and 2) by hosting populations of beneficial as well as phytophagous arthropods that can provide significant stability to the agroecosystem. The present study sampled the arthropod fauna in this stratum. The research was conducted in an apple orchard with organic certification since 1998. A plot of 10 ha was divided into four treatment areas of 2.5 ha each: 1) permanent cover of fescue (Festuca arundinacea) plus alfalfa (Medicago sativa), AF; 2) permanent cover of strawberry clover (Trifolium fragiferum) seeded in 1999 and 2002, SC; 3) seeding of common vetch (Vicia sativa) every March as a winter cover crop V; and 4) control (natural vegetation of grasses and legumes which is disked in late winter, the traditional management system by growers in this region), C. In order to compare the biodiversity of arthropods under organic management with conventional management (synthetic insecticides and herbicides), a fifth treatment was included in a nearby orchard with the same variety and rootstock (CH). Sampling between October and March began in 2000 and concluded in 2005. For pest control, sexual pheromones and botanical, biological, and mineral insecticides were used. Different sampling techniques were performed to determine the abundance of arthropods. Coleoptera, Formicidae, Araneae, and Dyptera, in this order, were the most numerous groups (75%). Isopods, hymenopterans, and homopterans represented less than 20% of the total. Of the collected species, 52.9% were phytophagous, and 41.9% were biological controllers (BC). AF presented 59.9% BC and SC 56.2%. The BC collected were mainly coleopterans (Carabidae, Staphylinidae, and Coccinellidae), parasitoid hymenopterans, spiders, predator bugs (Nabidae, Geocoridae, and Anthocoridae) and lacewings. In general, C and CH showed the lowest indices of diversity. The highest diversity was observed in AF and SC. Armadillidium vulgare was almost exclusively collected in the organic sector and could be considered as a biological indicator. In general, the number of BC and their diversity increased with the presence of cover crops and decreased with the utilization of agrochemicals.