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  • 1
    Article
    Article
    Language: English
    In: Journal of Applied Entomology, April, 2010, Vol.134(3), p.164(1)
    Description: To authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1439-0418.2010.01521.x Byline: Stefan Vidal
    ISSN: 0931-2048
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Oecologia, 2013, Vol.171(1), pp.249-259
    Description: Agricultural intensification has been shown to result in a decline in biodiversity across many taxa, but the changes in community structure and species interactions remain little understood. We have analysed and compared the structure of feeding interactions for cereal aphids and their primary and secondary parasitoids in organically and conventionally managed winter wheat fields using quantitative food web metrics (interaction evenness, generality, vulnerability, link density). Despite little variation in the richness of each trophic group, food web structures between the two farming systems differed remarkably. In contrast to common expectations, aphids and primary parasitoids were characterized by (1) a higher evenness of interaction frequencies (interaction evenness) in conventional fields, which cascaded to interactions at the next trophic level, with (2) a higher interaction evenness, (3) a higher ratio of primary parasitoid taxa per secondary parasitoid (generality) and (4) a higher link density. Aphid communities in the organically managed fields almost exclusively consisted of a single ear-colonizing species, Sitobion avenae , while highly fertilized conventional fields were mainly infested by leaf-colonizing aphids that benefit from the nutritional status of winter wheat. In conclusion, agricultural intensification appears to foster the complexity of aphid–parasitoid food webs, thereby not supporting the general expectation on the importance of organic farming practices for species richness and food web complexity.
    Keywords: Agricultural intensification ; Organic farming practices ; Biodiversity ; Interaction structures ; Sitobion avenae
    ISSN: 0029-8549
    E-ISSN: 1432-1939
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  • 3
    In: PLoS ONE, 2013, Vol.8(1)
    Description: Aphids feed on plant phloem sap, rich in sugars but poor in essential amino acids. However, sugars cause osmotic regulation problems for aphids, which they overcome by hydrolysing the sugars in their gut and polymerising the hydrolysis products into oligosaccharides, excreted with honeydew. Aphids harbour primary bacterial endosymbionts, which supply them with essential amino acids necessary for survival. They also harbour secondary (facultative) endosymbionts (sfS), some of which have a positive impact on life history traits, although it is not yet known whether they also play a role in providing effective tolerance to differing levels of water soluble carbohydrates (WSCs). We investigated the relationship between WSC content of cocksfoot cultivars and performance of clones of the English grain aphid Sitobion avenae F. We evaluated how clone genotype and their sfS modulate performance on these different cultivars. We therefore examined the performance of genetically defined clones of S. avenae , collected from different host plants, harbouring different sfS. The performance was tested on 10 Dactylis glomerata L. cultivars with varying WSC content. D. glomerata is known as a wild host plant for S. avenae and is also commercially planted. We found that high WSCs levels are responsible for the resistance of D. glomerata cultivars to specific S. avenae clones. The minimum level of WSCs conferring resistance to D. glomerata cultivars was 1.7% dw. Cultivars with a WSC content of 2.2% or higher were resistant to S. avenae and did not allow reproduction. Our results further indicate that sfS modulate to some extend host plant cultivar adaptation in S. avenae . This is the first study revealing the importance of WSCs for aphid performance. Cocksfoot cultivars with a high content of WSCs might be therefore considered for aphid control or used for resistance breeding in this and other grass species, including cereals.
    Keywords: Research Article ; Agriculture ; Biology
    E-ISSN: 1932-6203
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  • 4
    Language: English
    In: 2012, Vol.7(10), p.e44685
    Description: The western corn rootworm (WCR) is one of the economically most important pests of maize. A better understanding of microbial communities associated with guts and eggs of the WCR is required in order to develop new pest control strategies, and to assess the potential role of the WCR in the dissemination of microorganisms, e.g., mycotoxin-producing fungi. ; Total community (TC) DNA was extracted from maize rhizosphere, WCR eggs, and guts of larvae feeding on maize roots grown in three different soil types. Denaturing gradient gel electrophoresis (DGGE) and sequencing of 16S rRNA gene and ITS fragments, PCR-amplified from TC DNA, were used to investigate the fungal and bacterial communities, respectively. Microorganisms in the WCR gut were not influenced by the soil type. Dominant fungal populations in the gut were affiliated to spp., while was the most abundant bacterial genus. Identical ribosomal sequences from gut and egg samples confirmed a transovarial transmission of sp. Betaproteobacterial DGGE indicated a stable association of sp. with the WCR gut. Dominant egg-associated microorganisms were the bacterium sp. and the fungus ; The soil type-independent composition of the microbial communities in the WCR gut and the dominance of only a few microbial populations suggested either a highly selective environment in the gut lumen or a high abundance of intracellular microorganisms in the gut epithelium. The dominance of species in the guts indicated WCR larvae as vectors of mycotoxin-producing fungi. The stable association of sp. with WCR gut systems and the absence of corresponding sequences in WCR eggs suggested that this bacterium was postnatally acquired from the environment. The present study provided new insights into the microbial communities associated with larval guts and eggs of the WCR. However, their biological role remains to be explored.
    Keywords: Research Article ; Agriculture ; Biology ; Plant Biology ; Microbiology
    E-ISSN: 1932-6203
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  • 5
    Language: English
    In: PLoS ONE, 01 January 2017, Vol.12(7), p.e0180807
    Description: The rape stem weevil, Ceutorhynchus napi Gyll., is a serious pest of winter oilseed rape (Brassica napus L.) crops in Europe causing severe yield loss. In currently used oilseed rape cultivars no resistance to C. napi has been identified. Resynthesized lines of B. napus have potential to broaden the genetic variability and may improve resistance to insect pests. In this study, the susceptibility to C. napi of three cultivars, one breeding line and five resynthesized lines of oilseed rape was compared in a semi-field plot experiment under multi-choice conditions. Plant acceptance for oviposition was estimated by counting the number of C. napi larvae in stems. The larval instar index and the dry body mass were assessed as indicators of larval performance. The extent of larval feeding within stems was determined by the stem injury coefficient. Morphological stem traits and stem contents of glucosinolates were assessed as potential mediators of resistance. The resynthesized line S30 had significantly fewer larvae than the cultivars Express617 and Visby and the resynthesized lines L122 and L16. The low level of larval infestation in S30 was associated with a low larval instar and stem injury index. Low numbers of larvae were not correlated with the length or diameter of stems, and the level of stem glucosinolates. As indicated by the low larval infestation and slow larval development the resistance of S30 to C. napi is based on both antixenotic and antibiotic properties of the genotypes. The resynthesized line S30 should therefore be introduced into B. napus breeding programs to enhance resistance against C. napi.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 6
    In: PLoS ONE, 2013, Vol.8(3)
    Description: Cocoa agroforests can significantly support biodiversity, yet intensification of farming practices is degrading agroforestry habitats and compromising ecosystem services such as biological pest control. Effective conservation strategies depend on the type of relationship between agricultural matrix, biodiversity and ecosystem services, but to date the shape of this relationship is unknown. We linked shade index calculated from eight vegetation variables, with insect pests and beneficial insects (ants, wasps and spiders) in 20 cocoa agroforests differing in woody and herbaceous vegetation diversity. We measured herbivory and predatory rates, and quantified resulting increases in cocoa yield and net returns. We found that number of spider webs and wasp nests significantly decreased with increasing density of exotic shade tree species. Greater species richness of native shade tree species was associated with a higher number of wasp nests and spider webs while species richness of understory plants did not have a strong impact on these beneficial species. Species richness of ants, wasp nests and spider webs peaked at higher levels of plant species richness. The number of herbivore species (mirid bugs and cocoa pod borers) and the rate of herbivory on cocoa pods decreased with increasing shade index. Shade index was negatively related to yield, with yield significantly higher at shade and herb covers〈50%. However, higher inputs in the cocoa farms do not necessarily result in a higher net return. In conclusion, our study shows the importance of a diverse shade canopy in reducing damage caused by cocoa pests. It also highlights the importance of conservation initiatives in tropical agroforestry landscapes.
    Keywords: Research Article ; Agriculture ; Biology
    E-ISSN: 1932-6203
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  • 7
    Language: English
    In: Agriculture, Ecosystems and Environment, 01 August 2013, Vol.175, pp.54-59
    Description: Temperate grasses are infected with endophytic fungi of the genus . These fungi asymptomatically live inside the plant’s tissue enhancing resistance of their hosts to herbivores and abiotic stresses. Perennial ryegrass ( ), infected with can be detrimental to grazing livestock causing a neural disease. This study aimed at determining the impact of grassland management on fungal incidence. In a rural district of Central Germany 90 sites differing in land use intensity (extensive, intermediate and intensive) and grassland use (pastures, mown pastures, and meadows) were investigated for the presence of Infections were detected in 41% of the sites sampled, but overall infection rates were low (5.8 ± 9.2%). Neither the intensity of land use nor the type of grassland influenced endophytic incidences. In contrast, the geology of the sampled sites had a significant impact on the incidence of . Grass tillers collected from limestone sites showed significantly higher infection rates than from other soils. We hypothesize that the low field capacity and high amount of potassium on limestone sites favored the survival of infected grasses under drought stress. Therefore, geology should be taken into account when considering management strategies for this endophytic fungus.
    Keywords: Endophytic Fungus ; Grassland Management ; Lolium Perenne ; Drought Stress ; Environmental Stress ; Soil Type ; Agriculture ; Environmental Sciences
    ISSN: 0167-8809
    E-ISSN: 1873-2305
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  • 8
    Language: English
    In: Agriculture, ecosystems & environment, 2013, Vol.175, pp.54-59
    Description: Temperate grasses are infected with endophytic fungi of the genus Neotyphodium. These fungi asymptomatically live inside the plant’s tissue enhancing resistance of their hosts to herbivores and abiotic stresses. Perennial ryegrass (Lolium perenne), infected with Neotyphodium lolii can be detrimental to grazing livestock causing a neural disease. This study aimed at determining the impact of grassland management on fungal incidence. In a rural district of Central Germany 90 sites differing in land use intensity (extensive, intermediate and intensive) and grassland use (pastures, mown pastures, and meadows) were investigated for the presence of N. lolii. Infections were detected in 41% of the sites sampled, but overall infection rates were low (5.8±9.2%). Neither the intensity of land use nor the type of grassland influenced endophytic incidences. In contrast, the geology of the sampled sites had a significant impact on the incidence of N. lolii. Grass tillers collected from limestone sites showed significantly higher infection rates than from other soils. We hypothesize that the low field capacity and high amount of potassium on limestone sites favored the survival of infected grasses under drought stress. Therefore, geology should be taken into account when considering management strategies for this endophytic fungus. ; p. 54-59.
    Keywords: Limestone ; Herbivores ; Endophytes ; Pastures ; Acremonium Lolii ; Meadows ; Tillers ; Livestock ; Water Stress ; Range Management ; Grasses ; Fungi ; Lolium Perenne ; Hosts ; Potassium ; Field Capacity ; Neotyphodium ; Plant Tissues ; Land Use
    ISSN: 0167-8809
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 9
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 17 May 2011, Vol.108(20), pp.8311-6
    Description: Local and landscape-scale agricultural intensification is a major driver of global biodiversity loss. Controversially discussed solutions include wildlife-friendly farming or combining high-intensity farming with land-sparing for nature. Here, we integrate biodiversity and crop productivity data for smallholder cacao in Indonesia to exemplify for tropical agroforests that there is little relationship between yield and biodiversity under current management, opening substantial opportunities for wildlife-friendly management. Species richness of trees, fungi, invertebrates, and vertebrates did not decrease with yield. Moderate shade, adequate labor, and input level can be combined with a complex habitat structure to provide high biodiversity as well as high yields. Although livelihood impacts are held up as a major obstacle for wildlife-friendly farming in the tropics, our results suggest that in some situations, agroforests can be designed to optimize both biodiversity and crop production benefits without adding pressure to convert natural habitat to farmland.
    Keywords: Biodiversity ; Tropical Climate ; Agriculture -- Methods ; Trees -- Growth & Development
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 10
    Language: English
    In: Environmental entomology, February 2011, Vol.40(1), pp.111-9
    Description: The spatio-temporal distribution of Sahlbergella singularis Haglung, a major pest of cacao trees (Theobroma cacao) (Malvaceae), was studied for 2 yr in traditional cacao forest gardens in the humid forest area of southern Cameroon. The first objective was to analyze the dispersion of this insect on cacao trees. The second objective was to develop sampling plans based on fixed levels of precision for estimating S. singularis populations. The following models were used to analyze the data: Taylor's power law, Iwao's patchiness regression, the Nachman model, and the negative binomial distribution. Our results document that Taylor's power law was a better fit for the data than the Iwao and Nachman models. Taylor's b and Iwao's β were both significantly 〉1, indicating that S. singularis aggregated on specific trees. This result was further supported by the calculated common k of 1.75444. Iwao's α was significantly 〈0, indicating that the basic distribution component of S. singularis was the individual insect. Comparison of negative binomial (NBD) and Nachman models indicated that the NBD model was appropriate for studying S. singularis distribution. Optimal sample sizes for fixed precision levels of 0.10, 0.15, and 0.25 were estimated with Taylor's regression coefficients. Required sample sizes increased dramatically with increasing levels of precision. This is the first study on S. singularis dispersion in cacao plantations. Sampling plans, presented here, should be a tool for research on population dynamics and pest management decisions of mirid bugs on cacao.
    Keywords: Models, Biological ; Heteroptera -- Physiology ; Insect Control -- Methods
    ISSN: 0046225X
    E-ISSN: 1938-2936
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