Effects of native biodiversity on grape loss of four castes: testing the biotic resistance hypothesis

The agricultural practices strongly influence the biodiversity of agricultural areas, and the ecological services that these ecosystems provide. One of the services that have been most affected is the biological resistance to pests.Wine production is a common type of agriculture throughout the world, and it has a strong historical and economic importance for certain countries such as Portugal. But this type of agriculture is subject a high number of pests that affect the production, and farmers use pesticides to combat these pests, thus affecting the biodiversity that inhabits and uses the vineyards for food. This study took place in the Bairrada region in Central Portugal. We used six vineyards to assess the losses caused by fungi, birds and insects in four castes (Touriga, Baga, Arinto and Chardonnay), and evaluated whether pests have a preference for any caste or color (white and red). Bird and insect communities were studied and divided into functional guilds (pest, neutral or auxiliary), to compare with grape losses and assess if these natural communities hold a potential to naturally control wine pests (biotic resistance hypothesis). The edge effect in grape losses was also evaluated. We recorded a small proportion of grape losses, but we verified that insects had a preference for the Baga and Chardonnay castes. We observed that color did not influence the birds and insect's losses. In relation to the fungi losses, we registered a preference for the caste Baga. Most insects and birds observed in vineyards were pests, which entails a low level of biological control in this agricultural ecosystem. Although the relation between the edge and grape losses was not significant, there were more losses in the first 100 meters from the edge.Further studies will be necessaries to fully evaluate the role of local biodiversity in vineyards. To better evaluate the biotic resistance hypothesis it would be necessary to sample an organic vineyard, i.e. without the use of the pesticides.<br>