Henryk Luka

Overwintering of arthropods in soils of arable fields and adjacent semi-natural habitats

In order to determine the significance of field margins for the overwintering of arthropods in agricultural landscapes, different sites of an integrated and of an organically managed farm were investigated in the northwest of Switzerland. During December 1995 and January 1996, soil samples were taken with an electronic-hydraulic soil borer (depth: 25 cm, diameter: 8 cm). After hand sorting the larger arthropods, the small ones were extracted with a modified MacFadyen apparatus. The abundance of arthropods in the arable fields was significantly lower than in the adjacent semi-natural habitats. Highest abundances and species diversities were found in a sown wildflower strip, a hedge, a permanent meadow and a meadow under the cherry trees of the organic farm. With a total of 90 arthropod species in the semi-natural habitats, five times more species were found than in the arable fields. Staphylinids, carabids, spiders and chilopods were the most abundant arthropod groups. The data showed that undisturbed semi-natural habitats and extensively managed field margins play a key role as overwintering sites for many predatory arthropods.

Quantifying the impact of landscape and habitat features on biodiversity in cultivated landscapes

Determining habitat and landscape features that lead to patterns of biodiversity in cultivated landscapes is an important step for the assessment of the impact of extensification programmes in agriculture. In the context of an assessment of the effect of national extensification programme on biodiversity in agriculture, field data of three regions (7 km 2 each) were collected according to a stratified sampling method. A distribution model of three taxa (spiders, carabid beetles, and butterflies) is related to influencing factors by means of multivariate statistics (canonical correspondence analysis (CCA), partial CCA). Hypothetical influencing factors are categorised as follows: (1) habitat (habitat type, plant species richness) and (2) landscape (habitat heterogeneity, variability, diversity, proportion of natural and semi-natural areas). The correlative model developed for the spider assemblages revealed that the most important local habitat factors are those directly influenced by management practices. Landscape variability, heterogeneity and diversity in the surroundings are not significant factors. Carabid beetle assemblages show a positive reaction to landscape features and respond to particular cultivated surroundings. The model developed for butterflies shows that species assemblages are sensitive to landscape features. Surrounding land use in particular, has a major influence. There are no general models relating overall species diversity to landscape diversity. The relationship strongly depends on the organism examined. Therefore, biodiversity response to landscape and habitat changes (e.g. the extensification programme) has to be identified by means of multi-taxon concept.

Effects of low-input farming systems on carabids and epigeal spiders – a paired farm approach

We compared the effects of different low-input farming systems on carabids and spiders. The study was performed in a 3-year field survey using a paired-farm approach in six different landscapes units in northwestern Switzerland considering also the nearby semi-natural habitats. Carabids and spiders were sampled in 24 winter cereal crops and 18 semi-natural habitats using five funnel pitfall traps per site. Considering all cereal sites, in low-input ICM fields (= no insecticides, fungicides and growth regulators; ICM: Integrated crop management) 36% less carabids and 8% less spider specimens were found. In several cases, carabid populations of organic fields were significantly richer in species and abundance than in the low-input integrated crop management farmed plots. Endangered, stenoceous carabids (e.g. xero-thermophilous) and top-predators were more abundant in the organic fields. Spider communities differed less in mean number of species and abundance between the two low-input agricultural systems. Multivariate analysis showed that farming method and weed abundance were significant factors altering the carabid fauna and weed diversity influence spider fauna. Wolfspiders such as Pardosa agrestis, P. palustris and Trochosa ruricola seem to be enhanced by organic management. Linyphiids (Erigone atra, Oedothorax apicatus) were more abundant in lowinput ICM fields. Several carabid species and wolfspiders which have their main distribution in semi-natural habitats occurred more abundant in organic fields. This indicates that seminatural habitats in combination with organic farming may be an important factor for the conservation and enhancement of the species rich assemblages on agricultural land. Auswirkungen von zwei extensiven Anbausystemen auf die Laufkafer- und Spinnenfauna wurden unter Berucksichtigung der im Umfeld liegenden naturnahen Habitate untersucht. Sechs vergleichbare Paarbetriebe in sechs Landschaften der Nord-Westschweiz wurden wahrend einer 3-jahrigen Untersuchung dazu ausgewahlt. Die epigaischen Nutzarthropoden wurden mittels 5 Trichterbodenfallen in 24 Wintergetreideflachen und 18 naturnahen Flachen erfasst. Uber alle Ackerstandorte betrachtet wurden in den extensiv, integriert (IP) bewirtschafteten Getreideflachen (keine Anwendung von Fungiziden, Insektiziden und Wachstumsregulatoren) 36% weniger Laufkafer und 8% weniger Spinnentiere gefunden. In einigen Vergleichsfallen waren die durchschnittliche Artenvielfalt und Aktivitatsdichte der Laufkafer in den biologisch bewirtschafteten Wintergetreideflachen signifikant hoher als in den IP-Extenso Flachen. Gefahrdete, stenoke (z.B. xero-thermophile) Laufkaferarten und Top-Pradatoren waren in den biologisch bewirtschafteten Flachen zahlreicher. Bei der Spinnenfauna ergaben sich weniger deutliche Unterschiede betreffend durchschnittlicher Artenzahl und Aktivitatsdichte. Multivariate Analysen zeigten, dass die Anbaumethode und die Dichte der Begleitflora die Laufkafer signifkant beein

Ecological cross compliance promotes farmland biodiversity in Switzerland

In ecological cross compliance, farmers have to meet environmental standards in order to qualify for area-related direct payments. Because this is a strong financial incentive, cross compliance is a potentially powerful policy instrument. We monitored the effectiveness of cross compliance in promoting biodiversity on grassland and on arable land in Switzerland over 8 years. We observed measurable benefits for flora, butterflies, ground beetles, and spiders, in terms of species numbers and/or community composition. However, populations of threatened species showed no signs of benefit. While cross compliance has been in force in Switzerland for almost a decade, it has only recently been introduced in the neighboring European Union. We argue that – provided the environmental standards relating to biodiversity are increased in the future –common farmland biodiversity could be enhanced at the continental scale under cross compliance. The Swiss example shows that appropriate cross-compliance standards benefit farmland biodiversity at field and farm scales, while the conservation of threatened species needs to be addressed by specific programs, acting at the scale of agricultural landscapes.

Noncrop flowering plants restore top‐down herbivore control in agricultural fields

Abstract Herbivore populations are regulated by bottom-up control through food availability and quality and by top-down control through natural enemies. Intensive agricultural monocultures provide abundant food to specialized herbivores and at the same time negatively impact natural enemies because monocultures are depauperate in carbohydrate food sources required by many natural enemies. As a consequence, herbivores are released from both types of control. Diversifying intensive cropping systems with flowering plants that provide nutritional resources to natural enemies may enhance top-down control and contribute to natural herbivore regulation. We analyzed how noncrop flowering plants planted as “companion plants” inside cabbage (Brassica oleracea) fields and as margins along the fields affect the plant–herbivore–parasitoid–predator food web. We combined molecular analyses quantifying parasitism of herbivore eggs and larvae with molecular predator gut content analysis and a comprehensive predator community assessment. Planting cornflowers (Centaurea cynanus), which have been shown to attract and selectively benefit Microplitis mediator, a larval parasitoid of the cabbage moth Mamestra brassicae, between the cabbage heads shifted the balance between trophic levels. Companion plants significantly increased parasitism of herbivores by larval parasitoids and predation on herbivore eggs. They furthermore significantly affected predator species richness. These effects were present despite the different treatments being close relative to the parasitoids’ mobility. These findings demonstrate that habitat manipulation can restore top-down herbivore control in intensive crops if the right resources are added. This is important because increased natural control reduces the need for pesticide input in intensive agricultural settings, with cascading positive effects on general biodiversity and the environment. Companion plants thus increase biodiversity both directly, by introducing new habitats and resources for other species, and indirectly by reducing mortality of nontarget species due to pesticides. This study provides a comprehensive assessment of how habitat manipulation affects biocontrol services of a natural enemy community including both parasitoids and generalist predators. The trophic interactions between pests, parasitoids and predators were determined to achieve a better systemic understanding of top-down herbivore control, which can be strengthened when natural enemies complement each other or dampened by intraguild interactions. Our approach to selectively enhance the third trophic level to counteract specific herbivores was successful for both predators and parasitoids. Our results show significant positive effects of companion plants on predation of pest eggs and parasitism of pest larvae. Importantly, our data also suggest that carabids, staphylinids and spiders do not substantially interfere with parasitoid biocontrol as parasitoid DNA was rarely detected in predator guts.