Abstract
Chestnut (Castanea sativa Mill.) is one of the economically more important trees in the north of Portugal. Spiders, as generalist predators, are potential controlling agents of pests, yet the composition of the community of spiders associated with this crop is only poorly known. The objective of this study was to determine the spider communities in the canopies of chestnut trees subject to three different soil management practices in northeastern Portugal. Three chestnut groves each subject to a different agricultural practice (grazed, tilled or untilled) were studied in 2008 and 2009. The Araneae communities were sampled by beating the branches and the individuals collected were identified to family and species when possible. To investigate the structure of the spider community in each grove the abundance and family richness of spiders were calculated and compared between managements. In total, 4172 spiders were collected and, in both years, the three most abundant families were Araneidae, Philodromidae and Linyphiidae. In 2008, there was a greater abundance of spiders in the grazed, followed by the tilled and untilled groves, but no significant differences among groves. However, in 2009 there was a greater abundance of spiders in the tilled grove, followed by grazed and untilled groves and the differences between the untilled and the other two groves were significant. Araniella, Oxyopes and Anyphaena were the most abundant genera in the three groves. This study showed that soil management may influence the diversity of spiders, but the effects were weak and not consistent between years. The reduction or absence of a suitable habitat for spiders under the trees in the tilled treatment might have resulted in the spiders migrating up into the canopy. However, based on the weak effects on spider abundance recorded and its potentially adverse effects on soils, tillage is not recommended for managing the incidence of pests in chestnut groves.
Highlights
Chestnut (Castanea sativa Mill.) is traditionally cultivated tree in the north of Portugal because it is well adapted to growing in the local soils and of its social and economical importance (Monteiro, 2000)
The objective of this study was to determine the spider communities in the canopies of chestnut trees growing under different soil management practices in the
In 2008, there was a greater abundance of spiders in the grazed grove followed by the tilled and untilled groves (Table 1)
Summary
Chestnut (Castanea sativa Mill.) is traditionally cultivated tree in the north of Portugal because it is well adapted to growing in the local soils (moderately deep and well drained sandy-loam soils) and of its social and economical importance (Monteiro, 2000). The main pests of this crop are tortricids (Cydia spp.) and curculionids (Curculio spp.), which can cause losses of up to 50% of the seed production Other phytophagous species such as mites, aphids, psyllids and diaspidids are frequently recorded in chestnut trees It is not possible to use chemical control due to the lack of accredited products for use against pests of chestnut in Portugal (Oliveira, 2011) and there is a need to use biological control agents against these pests.
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