Jan Lagerlöf

Habitat preferences of nest-seeking bumble bees (Hymenoptera: Apidae) in an agricultural landscape.

The aim of this study was to find out where bumble bee queens place their nests in the agricultural landscape. Nest-seeking behaviour was used to indicate nesting site preferences. Four types of agricultural landscape were investigated near Uppsala, Sweden: open, relatively open, relatively wooded and wooded. Twelve 500-metre-long transects, each including several intermingled habitats (e.g., field boundaries, pastures, clearings), were inspected repeatedly over a two-month period, from April to June 1991. In total, 147 observations of bumble bee queens (Bombus spp.) of eight species were recorded. Nest-seeking queens were observed most frequently along forest boundaries and field boundaries, in open uncultivated areas and in the relatively open landscape, whereas they were least frequent in forest and in clearings. Fields, pastures and road boundaries had intermediate frequencies. Differences among species were found in terms of both landscape type and habitat preferences: B. terrestris, B. lapidarius, B. sylvarum and B. subterranius preferred open terrain, whereas B. lucorum and B. pascuorum preferred forest boundaries. Withered grass and tussocks were the preferred nest-seeking patches among all species.

The abundance of arthropods along two field margins with different types of vegetation composition: an experimental study

The effects of vegetation types and reclamation measures on the abundance of certain functional groups of above-ground and soil arthropods (i.e. herbivores, predators and parasitoids) were studied. The study sites were a field margin totally dominated by couch grass, Elytrigia repens (L.) Nevski, a serious weed, and a field margin with a naturally diverse flora. The couch-grass dominated margin was in part ploughed and sown with leguminous plants, or left as fallow for natural succession of vegetation. The field margin with a naturally diverse flora harboured the highest abundance and diversity of all studied arthropod groups. However, couch grass, especially the dense vegetation and deep sod layer, appeared to be an important refuge for many groups, particularly predatory insects. Both the created leguminous and the weed-dominated natural successions were frequently visited by pollen- and nectar-feeding insects, while arthropods hibernating in the soil in late autumn were scarce. Except for the occurrence of blossom beetles associated with rape plants, the studied field margins were not found to harbour high numbers of any particular pest insect. The importance of field margins for faunal diversity in the agricultural landscape, and the possibility of improving the conditions for beneficial (predatory/ pollinating) arthropods are discussed.

Influence of soil fauna on fungal plant pathogens in agricultural and horticultural systems

Abstract An understanding of the ecology of plant pathogens is crucial for the development of agricultural and horticultural growing systems that enhance plant health. One important group of organisms that influences plant pathogen survival and dispersal is the soil fauna. This review deals with known and possible interactions between soil animals and different groups of fungal plant pathogens. It is suggested that facultative saprophytes may be affected considerably by mycelial grazing by soil animals, while obligate pathogens may be more influenced by animals that ingest spores and other types of propagules. Both types of pathogens can also be influenced by indirect interactions with the soil fauna. Manipulating the soil environment for enhancement of beneficial soil animals that consume pathogens seems to be a realistic possibility for sustainable agriculture and horticulture.

The importance of field boundaries for earthworms (Lumbricidae) in the Swedish agricultural landscape

The aim of this study was to find out if field boundaries are refuges for earthworms from where they can spread out into the agricultural fields, thereby keeping up their abundance and biodiversity. The earthworm community was studied in: (1) a 640 m long field boundary; (2) the adjacent arable field at different distances from the boundary; (3) a pasture adjoining to the opposite side of the field near Uppsala in Sweden. Sampling was done in May and September. In contradiction to what was preconceived, the abundance and biomass of earthworms, both in the boundary and the pasture, was significantly lower than that in the agricultural field. The density increased towards the centre of the field. The trends were similar for both spring and autumn. The same species were found in the field, boundary and pasture, but Aporrectodea caliginosa was more dominant in the field than in the other habitats. The conclusion is that agriculture with manure, fertilisers, moderate soil cultivation and varying crops, in general, is favourable for earthworms, except for certain species. However, situations can occur when the earthworm populations in the field decline, and then boundaries may serve as sources from where re-immigration can take place.

Germination of Plasmodiophora brassicae resting spores stimulated by a non-host plant

Plant-induced germination of Plasmodiophora brassicae resting spores was studied in a laboratory experiment. Spore reaction was analysed in nutrient solution with exudates from growing roots of different plant species – one host plant (Brassica rapa var. pekinensis) and four non-host plants (Lolium perenne, Allium porrum, Secale cereale and Trifolium pratense) – and in controls with distilled water and nutrient solution. It was found that root exudates from L. perenne stimulated spore germination more than exudates from the other plants, including those from the host plant. The effect could not be explained by differences in the nutritional composition of the solutions due to differential uptake of the plant species, or by differences in root activity, measured as exudation of soluble sugars. This is the first time such a separation of factors has been done in analysing the influence of plants on P. brassicae germination. Although stimulation of P. brassicae resting spore germination is not restricted to the presence of host plants, it seems to vary depending on the plant species.

Establishment of vegetation in broadened field boundaries in agricultural landscapes

Three field experiments with broadened permanent field boundaries were established in agricultural landscapes near Uppsala (southern Sweden). One aim was to test methods for increasing the amount of non-cultivated areas with high plant species diversity and at the same time suppressing the occurrence of weeds. The treatments consisted of re-establishing or broadening boundary strips, sowing a mixture of ley grasses and clover, of wild meadow species, or planting bushes. All treatments were managed by yearly mowing and taking away of the plant material. The vegetation was examined on two occasions during a 10-year period. At the second occasion, a set of untreated field boundaries (reference boundaries) in the vicinity of each experiment was examined for comparison. Sowing meadow species changed the species composition substantially compared to untreated boundaries. Out of 32 sown species, 22 remained after 10 years. These species are normally found in well-managed meadows or pastures. Species that did not establish or disappeared tended to be either adapted to moist or to dry conditions. Sowing meadow species kept the abundance of weeds on a lower level than sowing clover and grasses or free regeneration at one site and kept weed abundance lower or at least not higher than in reference boundaries.

Effects of Major Disturbances in Different Agricultural Cropping Systems on Soil Macroarthropods

Abstract Macroarthropods of barley and perennial grass, lucerne and red clover leys in Sweden and British Columbia were sampled during 1980–1982. The fauna of the perennial crops in both sites diversified during the period as a consequence of natural increase and immigration. Predators such as carabid and staphylinid beetles rapidly moved into fields which previously had been subjected to intensive soil cultivation. Chironomid fly larvae and diplopods were greatly affected by disturbances. Fly larvae recovered rapidly and diplopods slowly. Some benefits of perennial cropping systems are discussed.

Interaction between a fungal plant disease, fungivorous nematodes and compost suppressiveness

Abstract We tested the hypothesis that the fungivorous nematodes Aphelenchoides spp. and Aphelenchus avenae can suppress damping-off caused by Rhizoctonia solani in cauliflower seedlings, and enhance the disease-suppressive effect of compost. In greenhouse experiments, we used two different composts mixed with peat (20% + 80%) and pure peat as growth substrates in growing pots. In each substrate, treatments were: (A) with R. solani and nematodes, (B) with R. solani, (C) with nematodes, (D) control without R. solani or nematodes. Treatment effects were measured as percentage of healthy seedlings 7, 10 and 14 days after start of the experiment. We conducted two different experiments with the treatments A–D; one with Aphelenchoides spp. and one with Aphelenchus avenae. Aphelenchoides spp.+R. solani (treatment A) had 85% healthy plants (= control without addition of fungi (D)) compared with 45% in R. solani without nematodes (B). Aphelenchus avenae suppressed damping-off significantly in all substrates, from almost 100% dead plants in peat with R. solani to 65% healthy plants in R. solani+A. avenae. One compost mixture had an intrinsic suppressive effect on damping-off, while plant health in the other compost mixture was not better than in 100% peat as growing substrate. There were no additive suppressive effects (enhancement) between nematode effects and the suppressive compost. The results demonstrate the ability of fungivorous nematodes to suppress plant diseases. The effects of fungivorous nematodes in combination with compost and other control measures on disease suppression need further attention. The usefulness of fungivorous nematodes in agriculture and horticulture is discussed.

Effects of fungivorous nematodes on corky root disease of tomato grown in compost-amended soil

Abstract The effect of fungivorous nematodes, Aphelenchus avenae and Aphelenchoides spp., against corky root disease of tomato caused by Pyrenochaeta lycopersici was investigated. Three different greenhouse trials were conducted using soil naturally infested with P. lycopersici, alone or mixed with four different types of compost consisting of green manure, garden waste and horse manure (20% compost by volume). The fungivorous nematodes were propagated in cultures of the fungus Pochonia bulbillosa and inoculated (3 or 23 nematodes ml−1 substrate) into the soil and soil-compost mixtures one day after transplanting of tomato seedlings. Greenhouse experiments were terminated after ten weeks and disease was measured from infected roots after harvesting. Aphelenchus avenae significantly reduced the disease severity when added to infested soil without compost in all experiments. Aphelenchoides spp. did not suppress the disease either in the presence or absence of compost. Among the composts tested, only a garden waste compost was found to be suppressive to the disease. Neither A. avenae nor Aphelenchoides spp. improved the suppressive effect of the compost.

Single and Combined Effects of Pesticide Seed Dressings and Herbicides on Earthworms, Soil Microorganisms, and Litter Decomposition

Seed dressing, i.e., the treatment of crop seeds with insecticides and/or fungicides, aiming to protect seeds from pests and diseases, is widely used in conventional agriculture. During the growing season, those crop fields often receive additional broadband herbicide applications. However, despite this broad utilization, very little is known on potential side effects or interactions between these different pesticide classes on soil organisms. In a greenhouse pot experiment, we studied single and interactive effects of seed dressing of winter wheat (Triticum aestivum L. var. Capo) with neonicotinoid insecticides and/or strobilurin and triazolinthione fungicides and an additional one-time application of a glyphosate-based herbicide on the activity of earthworms, soil microorganisms, litter decomposition, and crop growth. To further address food-web interactions, earthworms were introduced to half of the experimental units as an additional experimental factor. Seed dressings significantly reduced the surface activity of earthworms with no difference whether insecticides or fungicides were used. Moreover, seed dressing effects on earthworm activity were intensified by herbicides (significant herbicide × seed dressing interaction). Neither seed dressings nor herbicide application affected litter decomposition, soil basal respiration, microbial biomass, or specific respiration. Seed dressing did also not affect wheat growth. We conclude that interactive effects on soil biota and processes of different pesticide classes should receive more attention in ecotoxicological research.