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Ben-Gurion University of the Negev (2008)

Herbivores suppression by generalist predators in desert agroecosystems

Gavish-Regev, Efrat

Titre : Herbivores suppression by generalist predators in desert agroecosystems

Auteur : Gavish-Regev, Efrat

Université de soutenance : Ben-Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2008

Résumé partiel
Agricultural landscapes are heterogeneous ecosystems that consist of a mosaic of patches in time and space and consist of both arable and non-arable components. Arthropods living in arable annual crops suffer mortality caused by agricultural practices such as tilling, harvest and pesticide applications. In such systems, natural enemies must survive in the fields between successive cropping seasons, or recolonize the crop fields from the surrounding natural habitats each season. Therefore, migration from surrounding habitats is crucial in order to maintain populations of natural enemies of insect pests in crops. The goal of my research was to investigate the role of spiders (Arachnida : Araneae) as natural enemies of insect pests in a desert agroecosystem, and to understand the spatial dynamics of spiders in arid agroecosystems. Desert agroecosystems differ from temperate ones in their pronounced contrast between crop and natural habitats, where irrigated and fertilized crops are islands of high productivity in an arid matrix. These contrasting conditions between arable and non-arable habitats in arid regions could either enhance or hamper movement of spiders between these landscape components. Therefore I assumed that the potential for pest suppression by spiders will be influenced by the movement patterns of spiders between the natural desert habitats and crop fields. Furthermore, I suggested that availability and density of additional non-pest prey and the presence of other predators will affect pest suppression by spiders in the system. Initially, I examined the importance of the surrounding arid habitats as a source of spiders in wheat crops in the Negev desert of Israel. To do so, I sampled spiders in both arid natural habitat and adjacent wheat fields using pitfall traps and visual searches. In addition, I sampled spiders in wheat fields during winter, using emergence traps at increased distance from the field edge. I used stationary and movable emergence traps to distinguish between crop resident species from those that migrant into the fields from surrounding habitats. I found that the spider assemblage in wheat was dominated by three families : Linyphiidae, Theridiidae and Gnaphosidae, and recognized four functional groups that differ in habitat preference, movement patterns and population dynamics. Thirty three percent of the collected individuals were classified as crop residents, whereas more than 50% were migrants from the surrounding habitats. Spider assemblage in wheat fields was dominated by migrant species that arrive from the surrounding natural habitats and inhabit the crop throughout the season. From extensive sampling I concluded that the surrounding habitats influence the composition of spider assemblage in the fields, in spite of the marked contrast in structure and productivity between the adjacent managed and natural habitats. I proposed that the combined contribution of resident and migrant functional groups could potentially suppress insect pest populations in this desert agroecosystem.

Mots Clés : Agricultural pests — Israel — Negev — Biological control. — Aphids — Israel — Negev — Biological control. — Arid regions agriculture — Israel — Negev. — Biotic communities — Israel — Negev. — Herbivores — Israel — Negev — Biological control. — Predatory insects — Israel — Negev. — Spiders — Israel — Negev. — Wheat — Diseases and pests — Control — Israel.

Présentation (BGU )

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Page publiée le 19 mai 2012, mise à jour le 21 novembre 2018