Effect of Organic Farming and Agricultural Abandonment on Beneficial Arthropod Communities Associated with Olive Groves in Western Spain: Implications for Bactrocera oleae Management

Abstract

Agricultural abandonment and intensification are among the main land-use changes in Europe. Along with these processes, different proposals have been developed to counteract the negative effects derived from agricultural intensification, including organic management. In this context, we aimed to determine how organic management and farmland abandonment affect Bactrocera oleae and its main groups of natural enemies: hymenopteran parasitoids, spiders, ants, carabids, and staphylinids. Between May and October 2018, four samplings were carried out in nine olive groves (three under organic management, three under traditional management, and three abandoned) in a rural area on the border between Spain and Portugal (Salamanca, Western Spain). Our results suggested differences between the natural enemy community composition of abandoned and organic groves, with slightly higher levels of richness and abundance in abandoned groves. We found no differences between organic and traditional groves. The managed olive groves sustained a different natural enemy community but were similarly rich and diverse compared with the more complex abandoned groves, with the latter not acting as a reservoir of B. oleae in our study area. Both systems may provide complementary habitats; however, further abandonment could cause a reduction in heterogeneity at the landscape scale and, consequently, a biodiversity loss.

Effects of Traditional Orchard Abandonment and Landscape Context on the Beneficial Arthropod Community in a Mediterranean Agroecosystem

“…These two types of orchards differ in vegetation architecture and microhabitats and resource availability (i.e., flowers, prey, hosts, refuge); therefore, they could be harboring species with distinct requirements. The spider community was richer and more abundant in abandoned orchards, which tend to have higher habitat structural complexity and resource availability, allowing them to sustain more species and individuals [ 25 , 33 ]. This is consistent with numerous studies that have shown that spiders are constrained by different habitat features at a local scale (e.g., [ 83 , 84 ]), being favored in habitats with increased prey availability [ 67 , 85 ] and more complex vegetation architecture [ 25 , 68 , 86 , 87 ].…”

“…The spider community was richer and more abundant in abandoned orchards, which tend to have higher habitat structural complexity and resource availability, allowing them to sustain more species and individuals [ 25 , 33 ]. This is consistent with numerous studies that have shown that spiders are constrained by different habitat features at a local scale (e.g., [ 83 , 84 ]), being favored in habitats with increased prey availability [ 67 , 85 ] and more complex vegetation architecture [ 25 , 68 , 86 , 87 ]. In fact, only three families were more abundant in traditional orchards: lycosids, gnaphosids, and linyphids (ground runners and sheet web weavers [ 88 ]), which are favored by the more open habitat of traditional orchards [ 25 , 68 , 89 , 90 ].…”

“…Agri-environmental payments (EPAC) have been focused on preventing the abandonment of traditional farming systems, which is considered one of the main drivers of biodiversity loss in Europe [ 112 ]. Nevertheless, research efforts to elucidate farmland abandonment consequences on biodiversity have been unequally distributed between annual and permanent crops, the latter being scarcely investigated [ 24 ], with only a few studies generally focused on olive groves, apple orchards, or vineyards, e.g., [ 20 , 23 , 25 ]. To our knowledge, our work constitutes the first attempt to analyze the effects of almond orchard abandonment on arthropod biodiversity, and it suggests that both abandoned and traditional almond orchards play an important role in conserving rich and abundant arthropod communities—but only in simple landscapes.…”

“…The majority of the studies on the effects of farmland abandonment have focused on grasslands or annual crops, especially in central Europe, whereas permanent crops and, in particular, traditional orchards, have received far less attention [ 24 , 25 ]. As ecological theory predicts, the consequences of agricultural abandonment (i.e., a further reduction in the disturbance level) may not be the same in annual systems and permanent crops given the low disturbance levels and increased stability of the latter [ 26 ].…”