Browsing by Person "Steidle, Johannes L. M."

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Disc mower versus bar mower: Evaluation of the direct effects of two common mowing techniques on the grassland arthropod fauna
(2025) von Berg, Lea; Frank, Jonas; Betz, Oliver; Steidle, Johannes L. M.; Böttinger, Stefan; Sann, Manuela
1. In Central Europe, species‐rich grasslands are threatened by intensive agriculture with frequent mowing, contributing to the reduction of arthropods such as insects and spiders. However, comprehensive and standardised studies on the direct effects of the two most agriculturally relevant mowing techniques, e.g., double‐blade bar mower versus disc mower, are lacking. 2. In a 2‐year experiment, we have investigated the direct effect of mowing on eight abundant arthropod groups in grassland, covering two seasonal mowing events in both years, using a randomised block design. We compared (a) an unmown control, (b) a double‐blade bar mower and (c) a disc mower. 3. For most of the taxonomic groups studied, a significantly lower number of individuals was found in the experimental plots immediately after mowing, regardless of the mowing technique, compared to an unmown control. This was not the case for Orthoptera and Coleoptera, which did not show a significant reduction in the number of individuals for both mowing techniques (Orthoptera) or only for the double‐blade bar mower (Coleoptera). 4. Between both mowing techniques, no significant differences were found for all taxonomic groups investigated. 5. Synthesis and applications: Our findings suggest that mowing in general has a negative impact on abundant arthropod groups in grassland, regardless of the method used. Tractor‐driven double‐blade bar mowers do not seem to be a truly insect‐friendly alternative to a conventional disc mower. Other factors such as cutting height and mowing regimes should be seriously considered to protect spiders and insects from the negative effects of mowing. In addition, we strongly recommend the maintenance of unmown refugia. Insects and spiders that are spared by mowing can take refuge in these unmown areas to avoid subsequent harvesting and thermally unfavourable conditions that arise on mown areas. Further, unmown refugia are basic habitat structures for a subsequent recolonisation of mown areas once the flora has recovered.
The emergence of ecotypes in a parasitoid wasp: a case of incipient sympatric speciation in Hymenoptera?
(2021) Malec, Pawel; Weber, Justus; Böhmer, Robin; Fiebig, Marc; Meinert, Denise; Rein, Carolin; Reinisch, Ronja; Henrich, Maik; Polyvas, Viktoria; Pollmann, Marie; von Berg, Lea; König, Christian; Steidle, Johannes L. M.
Background: To understand which reproductive barriers initiate speciation is a major question in evolutionary research. Despite their high species numbers and specific biology, there are only few studies on speciation in Hymenoptera. This study aims to identify very early reproductive barriers in a local, sympatric population of Nasonia vitripennis (Walker 1836), a hymenopterous parasitoid of fly pupae. We studied ecological barriers, sexual barriers, and the reduction in F1-female offspring as a postmating barrier, as well as the population structure using microsatellites. Results: We found considerable inbreeding within female strains and a population structure with either three or five subpopulation clusters defined by microsatellites. In addition, there are two ecotypes, one parasitizing fly pupae in bird nests and the other on carrion. The nest ecotype is mainly formed from one of the microsatellite clusters, the two or four remaining microsatellite clusters form the carrion ecotype. There was slight sexual isolation and a reduction in F1-female offspring between inbreeding strains from the same microsatellite clusters and the same ecotypes. Strains from different microsatellite clusters are separated by a reduction in F1-female offspring. Ecotypes are separated only by ecological barriers. Conclusions: This is the first demonstration of very early reproductive barriers within a sympatric population of Hymenoptera. It demonstrates that sexual and premating barriers can precede ecological separation. This indicates the complexity of ecotype formation and highlights the general need for more studies within homogenous populations for the identification of the earliest barriers in the speciation process.
The potential of farnesene isomer mixtures to support the control of aphids in the cultivation of lettuce crops
(2025) Kuhn, Denise; Bauer, Philipp; Tolasch, Till; Petschenka, Georg; Steidle, Johannes L. M.; Kuhn, Denise; Department of Chemical Ecology 190 T, Institute of Biology, University of Hohenheim, 70599, Stuttgart, Germany; Bauer, Philipp; Department of Applied Entomology 360 C, Institute of Phytomedicine, University of Hohenheim, 70599, Stuttgart, Germany; Tolasch, Till; Department of Chemical Ecology 190 T, Institute of Biology, University of Hohenheim, 70599, Stuttgart, Germany; Petschenka, Georg; Department of Applied Entomology 360 C, Institute of Phytomedicine, University of Hohenheim, 70599, Stuttgart, Germany; Steidle, Johannes L. M.; Department of Chemical Ecology 190 T, Institute of Biology, University of Hohenheim, 70599, Stuttgart, Germany
(E)-ß-farnesene (EBF) acts as an alarm pheromone of many aphid species and is also used as an aphid repellent by plants. Upon perception of EBF, aphids exhibit avoidance behavior. They walk away, stop feeding or drop from leaves. Moreover, EBF is an attractant for natural enemies of aphids. However, EBF is not used in pest management because it is expensive in its pure form. Therefore, we assessed the effect of a less expensive farnesene isomer mixture (FIM) on Myzus persicae (Sternorrhyncha: Aphidiae) on lettuce ( Lactuca sativa var. Ulmo) in the laboratory and under field conditions. First, we tested under laboratory conditions if FIM has the same effect on M. persicae as it is described for pure EBF. The aphids were influenced by EBF. They stopped feeding, withdrew their stylets, went away from the danger zone, or developed and reproduced more slowly. Therefore, we studied the behavioral response of the aphids after FIM application and aphid reproduction under permanent exposure of FIM. Second, we tested in the field the reaction to FIM either directly applied to lettuce or released by dispensers. In the lab experiments, we found that M. persicae reacts to FIM by walking away and that reproduction tends to be reduced in the presence of FIM. In the field, we found lower numbers of aphids in the treatments with FIM. In particular, dispenser application caused higher aphid reduction compared to spray application on lettuce. In addition, more natural enemies of aphids could be found in dispenser-treated plots. Taken together, these results indicate that the use of FIM could contribute to insecticide-free aphid control in lettuce, but possibly also in other crops.
Sex pheromone of the click beetle Agriotes pilosellus (Schönherr, 1718)
(2022) Tolasch, Till; von Fragstein, Maximilian; Steidle, Johannes L. M.; Tolasch, Till; Institut für Biologie, Universität Hohenheim, Stuttgart, Germany; von Fragstein, Maximilian; Institut für Biologie, Universität Hohenheim, Stuttgart, Germany; Steidle, Johannes L. M.; Institut für Biologie, Universität Hohenheim, Stuttgart, Germany
Agriotes pilosellus is a fairly common click beetle species distributed in open deciduous and mixed forests throughout a large area in Europe. To identify its sex pheromone, gland extracts of female beetles were analyzed using gas chromatography-mass spectrometry (GC-MS). The only volatile compounds present in the extracts were geranyl butanoate and ( E )-8-hydroxygeranyl dibutanoate in a 1:3 ratio, identified by comparison with synthetic samples. Field experiments revealed a clear attraction of A. pilosellus - males towards traps baited with geranyl butanoate, which could be synergistically enhanced by the factor of almost ten by addition of ( E )-8-hydroxygeranyl dibutanoate. The latter compound alone did not show any attractive effect. Both compounds correspond well to the structures known from other Agriotes species and may serve as an effective monitoring tool for entomofaunistic research.