Stefan Vidal

Universitätsmedizin Göttingen, Göttingen, Lower Saxony, Germany

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Publications (72)122.95 Total impact

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    ABSTRACT: Background: CO2 is known as an attractant for many soil-dwelling pests. To implement an attract-and-kill strategy for soil pest control, CO2 emitting formulations need to be developed. This work aimed at the development of a slow release bead system in order to bridge the gap between application and hatching of western corn rootworm larvae. Results: We compared different Ca-alginate beads containing Saccharomyces cerevisiae for their potential to release CO2 during several weeks. Addition of starch improved CO2 release resulting in significantly higher CO2 concentrations in soil for at least four weeks. The missing amylase activity was compensated either by microorganisms present in soil or by co-encapsulation of Beauveria bassiana. Formulations containing S. cerevisiae, starch and B. bassiana were attractive for western corn rootworm larvae within the first 4 h following exposure; however, when considering the whole testing period the maize root systems remained more attractive for the larvae. Conclusion: Co-encapsulation of S. cerevisiae, starch and B. bassiana is a promising approach for the development of attractive formulations for soil applications. For biological control strategies, the attractiveness needs to be increased by phagostimuli to extend contact between larvae and the entomopathogenic fungus growing out of these formulations.
    No preview · Article · Feb 2016 · Pest Management Science

  • No preview · Conference Paper · Sep 2015
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    ABSTRACT: Since several years it is known that strains of the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Ascomycota: Hypocreales) are able to colonize plants as a true endophyte. However, so far no integrated bioprocess engineering approaches have been published where fermentation and formulation strategies are combined to optimize colonization of oilseed rape plant tissues. We therefore aimed at investigating whether and how blastospore (BS) formation can be shifted to resilient submerged conidiospores (SCS) by introducing osmotic stress in different growth phases. When 50 g/L NaCl was added after 48 h to a culture of B. bassiana a yield of 1.4 ± 0.1x1010 SCS/g sucrose in shake flasks and 1.8 ± 0.1x1010 SCS/g sucrose in a stirred tank reactor were obtained. In a bioreactor, 24 h after the addition of NaCl, the formation of BS slowed down, the respiratory quotient decreased and a shift from BS to SCS set in. Following these steps, different formulation strategies, namely encapsulation, film coating and liquid formulation were evaluated. B. bassiana grew out of beads as well as on commercial fungicide-coated seeds. Due to the complete suppression of fungal growth on non-sterile soil, the most suitable option was a foliar application. A liquid formulation consisting of 0.1 % Triton X-114, 1 % molasses, 1 % titanium dioxide and 106 spores/mL was applied on leaf tips. After 14 days, the endophyte was detected by PCR and microscopic analysis in the leaves. Further research should focus on formation of SCS and protection of plants colonized by B. bassiana against herbivorous insects.
    Full-text · Article · Sep 2015 · Biological Control
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    ABSTRACT: Several vectoring insects, such as aphids and white fly, harbour secondary bacterial endosymbionts. When an insect vectors a persistently transmitted plant virus, this virus should pass through the insect gut into the haemolymph. The secondary bacteria, however, may affect the movement, persistence and replication of the viruses, thereby influencing the vectoring efficacy or specificity of the insect in respect to these plant viruses. This issue, however, has not yet been fully investigated. Hence, the aim of this primary study is to investigate the effect of secondary bacterial endosymbionts of Sitobion avenae clones in respect of the vector specificity and transmission efficiency of barley yellow dwarf virus, as well as to highlight in general the role of secondary bacteria in virus transmission. The experiments were performed according to standard protocols using one virus strain, BYDV-PAV, and four S. avenae clones harbouring different bacterial and genetic profiles. We found that all tested clones were able to transmit the tested virus strain. Therefore, it can be concluded that the secondary bacterial endosymbionts may affect transmission efficiency of S. avenae but not their vectoring specificity. That said, the clones did not significantly differ in their efficiency of virus transmission. However, this study is initial evidence of the effect of secondary bacteria endosymbionts of aphids on virus transmission and further investigation is, therefore, still required.
    No preview · Article · Sep 2015 · African Entomology

  • No preview · Conference Paper · Aug 2015
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    ABSTRACT: Aphids have developed symbiotic associations with different bacterial species, and some morphological and molecular analyses have provided evidence of the host relationship between the primary symbiotic bacteria (Buchnera aphidicola) and the aphid while the contrary with the secondary symbiotic bacteria. In this study, we investigated the phylogenetic relationships of the bacterial endosymbionts in the aphid Sitobion avenae (F.). We characterized all bacterial endosymbionts in 10 genetically defined S. avenae clones by denaturing gradient gel electrophoresis and, from these clones, sequenced the 16S rRNA genes of both the primary endosymbiont, B. aphidicola (for the first time), and the secondary endosymbionts, Regiella insecticola and Hamiltonella defensa (for the first time). The phylogenetic analysis indicated that Buchnera from Sitobion related to those in Macrosiphoni. The analysis of the secondary endosymbionts indicated that there is no host relationship between H. defensa and R. insecticola from Sitobion and those from other aphid species. In this study, therefore, we identified further evidence for the relationship between Buchnera and its host and reported a relationship within the secondary endosymbionts of S. avenae from the same country, even though there were no relationships between the secondary bacteria and their host. We also discussed the diversity within the symbiotic bacteria in S. avenae clones. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
    No preview · Article · Jul 2015 · Environmental Entomology
  • Stefan Vidal · Lara R. Jaber
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    ABSTRACT: It is now evident that entomopathogenic fungi are able to colonize plant tissues as symptomless endophytes. Although most data so far published in this regard refer to Beauveria bassiana as an endophytic fungus, two other entomopathogenic fungi, viz. Metarhizium anisopliae and Lecanicillium lecanii have also been shown to colonize plant tissues endophytically. Several recent studies have also shown reasonable detrimental effects on herbivorous insects feeding on plants harbouring these fungi as endophytes. However, data published so far are highly variable and not consistent with regard to the underlying mechanisms which would allow explaining these effects. Growth conditions, specific cultivar features, or interactions with other microorganisms may impact the effect of these endophytic entomopathogenic fungi on the herbivorous insects. Furthermore, other fungi may block the systemic growth of the fungi in plant parts distant to the point of inoculation. Other parameters which need to be taken into account for using these fungi as biocontrol agents are the level of mycotoxins produced in plants, the level of pest reduction and the nature of formulations allowing a consistent colonization of the crop plants. This review discusses these and other problems related to the use of entomopathogenic fungi as endophytic biocontrol agents.
    No preview · Article · Jul 2015 · Current science
  • J Junk · B Ulber · S Vidal · M Eickermann
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    ABSTRACT: Agricultural production is directly affected by projected increases in air temperature and changes in precipitation. A multi-model ensemble of regional climate change projections indicated shifts towards higher air temperatures and changing precipitation patterns during the summer and winter seasons up to the year 2100 for the region of Goettingen (Lower Saxony, Germany). A second major controlling factor of the agricultural production is the infestation level by pests. Based on long-term field surveys and meteorological observations, a calibration of an existing model describing the migration of the pest insect Ceutorhynchus napi was possible. To assess the impacts of climate on pests under projected changing environmental conditions, we combined the results of regional climate models with the phenological model to describe the crop invasion of this species. In order to reduce systematic differences between the output of the regional climate models and observational data sets, two different bias correction methods were applied: a linear correction for air temperature and a quantile mapping approach for precipitation. Only the results derived from the bias-corrected output of the regional climate models showed satisfying results. An earlier onset, as well as a prolongation of the possible time window for the immigration of Ceutorhynchus napi, was projected by the majority of the ensemble members.
    No preview · Article · Feb 2015 · International Journal of Biometeorology

  • No preview · Conference Paper · Sep 2014

  • No preview · Article · Jul 2014
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    C Agboton · A Onzo · F I Ouessou · G Goergen · S Vidal · M Tamò
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    ABSTRACT: Cashew, Anacardium occidentale L. (Sapindales: Anacardiaceae), is an important cash crop in Benin. However, its production is threatened by several biotic factors, especially insects. In Benin, very few studies have focused on insects and just listed species commonly found on cashew worldwide. The present investigation fills this gap by presenting an exhaustive inventory of insect species associated with this crop in the country. The survey was carried out from September 2009 to August 2010 in 22 cashew orchards (5 young and 17 mature) distributed over three major agroecological zones where cashew is most produced in the country. Insects were collected using chemical knock-down technique and visual observation followed by capture with sweep net. In addition, infested plant organs were sampled and incubated to collect emerging insects. In total, 262 insect species were recorded and identified. Among them, the wood borer Apate terebrans Pallas, the leafminer Eteoryctis gemoniella Stainton, and the mirid bugs Helopeltis schoutedeni Reuter., and Helopeltis anacardii Miller., appeared as the most important insect species attacking cashew in Benin. Beneficial insects encountered included some predators, parasitoids, and pollinators. Few vertebrate predators were also recorded on the trees. Differences in agroecological conditions or in field cleanliness did not affect the number of insect species encountered in the cashew orchards. The results of this study represent an important baseline data for the design and implementation of strategies for cashew protection in Benin.
    Full-text · Article · Jul 2014 · Journal of Insect Science
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    ABSTRACT: The larvae of the invasive maize pest Diabrotica virgifera virgifera (Coleoptera; Chrysomelidae, western corn rootworm) hatch in the soil in spring and search for maize roots following CO2 gradients. CO2 is one cue that might be used as an attractant towards soil insecticides, a mechanism already shown in laboratory experiments. This study compared the efficacy of several combinations of in or between-row applications of different rates of CO2-emitting capsules and/or soil insecticides (here tefluthrin) aimed at preventing root damage by the pest larvae under field conditions. CO2 emission of the capsules in the soil lasted up to 28 days with a peak after 21 days coinciding with the first larval hatch. The pest density in the soil was not high enough to cause root damage above the economic threshold. Furthermore all tefluthrin applications, regardless of whether at full, half or quarter rates effectively prevented root damage; thus CO2 did not significantly further increase this efficacy. In-row applications of tefluthrin with or without CO2-emitting capsules prevented root damage to a much larger extent (59–77 % on the node injury scale) than the between-row applications of tefluthrin with or without capsules (17–31 %). In conclusion, further research on belowground orientation and movement of D. v. virgifera larvae, as well as tests with combinations of CO2-emitting capsules and lower rates of soil insecticide are needed to potentially develop attract and kill strategies as a management option against this maize pest.
    Full-text · Article · Jun 2014 · Journal of Pest Science
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    Mario Schumann · Anant Patel · Marina Vemmer · Stefan Vidal
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    ABSTRACT: Western corn rootworm larvae use CO2 to locate maize roots. However, the importance of CO2 as a specific orientation cue close to maize roots is not unequivocally investigated. This study aimed at elucidating the effect of CO2 emitting capsules in combination with a soil insecticide (Tefluthrin = attract and kill) within the root system. We hypothesised that the capsules would result in an aggregation of the larvae at the soil insecticide, thus increasing its efficacy. A non-destructive observation device was used to study larval distribution and behaviour. Spatial analysis of distance indices (SADIE) revealed an aggregation of the larvae around the capsules in an attract and kill treatment after 4 hours which was not found at the conventional treatment without the capsules. However, larval mortality did not differ in both treatments. CO2 is a weak attractant for western corn rootworm larvae within the root system. Consequently, an attract and kill strategy based on a CO2 product will not contribute to a better control compared to conventional Tefluthrin applications. Host specific compounds, combined with a CO2 source, should be used to target more larvae, making attract and kill feasible as a management option against this pest.
    Full-text · Article · Apr 2014 · Pest Management Science
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    M Schumann · A Patel · S Vidal
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    ABSTRACT: Western corn rootworm (Diabrotica virgifera virgifera LeConte) larvae use carbon dioxide (CO2) to locate the roots of their hosts. This study investigated whether an encapsulated CO2 source (CO2-emitting capsules) is able to outcompete CO2 gradients established by corn root respiration in the soil. Furthermore, the following two management options with the capsules were tested in semifield experiments (0.5- to 1-m2 greenhouse plots): the disruption of host location and an "attract-and-kill" strategy in which larvae were lured to a soil insecticide (Tefluthrin) between the corn rows. The attract-and-kill strategy was compared with an application of Tefluthrin in the corn rows (conventional treatment) at 33 and 18% of the standard field application rate. Application of the CO2-emitting capsules 30 cm from the plant base increased CO2 levels near the application point for up to 20 d with a peak at day 10. Both the disruption of host location and an attract-and-kill strategy caused a slight but nonsignificant reduction in larval densities. The disruption of host location caused a 17% reduction in larval densities, whereas an attract-and-kill strategy with Tefluthrin added at 33 and 18% of the standard application rate caused a 24 and 27% reduction in larval densities, respectively. As presently formulated, the CO2-emitting capsules, either with or without insecticide, do not provide adequate control of western corn rootworm.
    Full-text · Article · Feb 2014 · Journal of Economic Entomology
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    ABSTRACT: The complex interactions among the maize pest Western Corn Rootworm (WCR), Glomus intraradices (GI-recently renamed Rhizophagus intraradices) and the microbial communities in both rhizosphere and endorhiza of maize have been investigated in view of new pest control strategies. In a greenhouse experiment, different maize treatments were established: C (control plants), W (plants inoculated with WCR), G (plants inoculated with GI), GW (plants inoculated with GI and WCR). After 20 days of WCR root feeding, larval fitness was measured. Dominant arbuscular mycorrhizal fungi (AMF) in soil and maize endorhiza were analyzed by cloning of 18S rRNA gene fragments of AMF, restriction fragment length polymorphism and sequencing. Bacterial and fungal communities in the rhizosphere and endorhiza were investigated by denaturing gradient gel electrophoresis of 16S rRNA gene and ITS fragments, PCR amplified from total community DNA, respectively. GI reduced significantly WCR larval development and affected the naturally occurring endorhiza AMF and bacteria. WCR root feeding influenced the endorhiza bacteria as well. GI can be used in integrated pest management programs, rendering WCR larvae more susceptible to predation by natural enemies. The mechanisms behind the interaction between GI and WCR remain unknown. However, our data suggested that GI might act indirectly via plant-mediated mechanisms influencing the endorhiza microbial communities.
    Full-text · Article · Dec 2013 · Frontiers in Microbiology
  • Anne Wilstermann · Stefan Vidal
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    ABSTRACT: Predicting western corn rootworm (Diabrotica virgifera virgifera LeConte; WCR) development in the field depends on models that use experimentally determined degree-days (°D). For constant temperature regimes, this temperature sum can be reliably used to predict hatch and development of WCR larvae. In the first experiment in climate cabinets, we evaluated the effects of varying day–night (4 and 6 °C difference) temperature regimes compared to equivalent constant temperature regimes on hatch, development, and recovery of WCR larvae from a non-diapausing population. Relative to constant diurnal temperatures, varying day–night temperatures resulted in earlier larval hatch and accelerated larval development (especially when day–night temperatures differed by 6 °C) due to direct temperature effects (i.e., the Kaufmann-effect) and to enhanced plant growth. For WCR eggs, the temperature sums needed for hatch in the field are overestimated when they are determined by models based on constant experimental temperatures. Recovery of larvae from soil was not affected by temperature, but was positively associated with plant height. In a second experiment we evaluated whether the found effect of varying temperature ranges on the acceleration of larval hatch is also influenced by the level of these varying temperatures. Initial hatch started earlier by varying diurnal temperatures only under a low-temperature regime (14 ± 4 °C). For herbivorous insects like WCR, plant growth effects induced by varying temperature regimes may result in increased variation in temperature-based developmental parameters. Consideration of these effects will improve models that predict WCR hatching patterns and will improve the development and timing of control strategies.
    No preview · Article · Sep 2013 · Journal of Pest Science
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    Full-text · Conference Paper · Aug 2013
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    ABSTRACT: 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.
    No preview · Article · Aug 2013 · Agriculture Ecosystems & Environment
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    ABSTRACT: 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.
    Full-text · Article · Jun 2013 · PLoS ONE
  • Katharina Lohaus · Stefan Vidal
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    ABSTRACT: Cereal aphids (Homoptera: Aphididae) are a periodical threat to winter wheat (Triticum aestivum L.) production worldwide, and outbreaks have been mainly related to increasing inputs of mineral fertilizers. The hypothesis of lower aphid abundance under organic fertilizer treatments, however, has not been tested at the species-specific level. In a 4-year study, we examined cereal aphid populations and plant parameters (dry biomass and nitrogen content) in winter wheat fields under low (legume-based), intermediate (legume-based plus organic liquid manure), and high (mineral) nitrogen intensities; low and intermediate intensities are characteristic of organic fields, while high intensities are inherent in conventional farming systems. Aphid species differed markedly in their response to fertilizer treatment. Unexpectedly, legume-based organic fields were related to higher abundances of the ear-colonizing species Sitobion avenae (F.), whereas manure-fertilized organic fields and conventional fields had significantly higher abundances of Metopolophium dirhodum (Wlk.) and Rhopalosiphum padi (L.). Nitrogen concentration of winter wheat increased with fertilizer intensity, and total aphid abundance (all species) was positively correlated with nitrogen content of grains in manure-fertilized organic fields and conventional fields, but was not correlated in legume-based organic fields dominated by S. avenae (89–96 % of the aphid community). Collectively, we demonstrate strong bottom-up effects that result in an improved performance of S. avenae in low-input systems. As total aphid abundance (all species) simultaneously decreased in legume-based organic fields, crop managers risk to underestimate pest damage by ignoring the impact of a single species, S. avenae, which has the greatest potential to reduce crop yield.
    No preview · Article · Jun 2013 · Organic Agriculture

Publication Stats

1k Citations
122.95 Total Impact Points

Institutions

  • 2009-2015
    • Universitätsmedizin Göttingen
      Göttingen, Lower Saxony, Germany
  • 2001-2015
    • Georg-August-Universität Göttingen
      • • Division of Agricultural Entomology
      • • Division of Plant Pathology and Plant Protection
      Göttingen, Lower Saxony, Germany
  • 2000
    • University of Bayreuth
      Bayreuth, Bavaria, Germany
  • 1998
    • Justus-Liebig-Universität Gießen
      • Institute of Phytopathology and Applied Zoology
      Gieben, Hesse, Germany