Effects of agri-environment management for cirl buntings on other biodiversity

Agri-environment scheme (AES) management has increased populations of cirl buntings (Emberiza cirlus) in South Devon, England, and might be expected to provide benefits for other declining biodiversity, due to less intensive farm management. Fields managed under AES for cirl buntings (low-input spring barley or permanent pasture without inputs) were contrasted with control fields under conventional management (spring barley without management restrictions and winter cereals, or grazed without management restrictions) to identify such benefits for vascular plants, butterflies, bumblebees, carabid beetles, foliar invertebrates and bats. Activity-density and species richness of carabid beetles were both higher in AES spring barley fields than in control spring barley and winter cereal fields. Forb cover and abundance of butterflies and bumblebees were higher in AES spring barley fields than in winter cereals, but did not differ between AES and control spring barley. No difference was observed in plant species richness between any of the arable field types. Plant species richness and butterfly abundance were higher in AES pasture fields than in controls. Abundance, activity-density and/or species richness of other taxa did not differ between AES and control pastures. Benefits observed in AES spring barley fields arise from management specific to AES agreements, and also, we suggest, from the maintenance of spring-sown barley in the landscape. Benefits in AES pasture fields are ascribed to the absence of fertiliser and pesticide inputs, and reductions in stocking arising from this; there is also likely to have been some pre-selection for older pastures to be entered into AES management agreements. Agri-environment measures for cirl buntings have benefits for a range of taxa beyond the target species, and therefore, largely through reduction of management intensity and maintenance of land-use diversity, improve the overall biodiversity of the farmed landscape where they are present.     

开封地区不同土地利用方式农田杂草群落结构及动态

2005年春、秋两季对开封地区不同土地利用方式小麦-玉米、小麦-大豆轮作地,葡萄地,弃耕地中杂草进行调查,统计分析各杂草群落中物种相似系数、物种相对多度分布、功能群相对多度和生物多样性。杂草功能群分为单子叶短期生植物（MA）、双子叶短期生植物（DA）、单子叶多年生植物（MP）及双子叶多年生植物（DP）4个功能类群。调查共记录杂草种类71种,隶属27个科;春季51种、共同种7个,秋季36种、共同种8个。不同土地利用方式杂草群落相似系数春季各群落间0．3～0．5,秋季玉米地-大豆地、秋葡萄地-弃耕地最高,分别是0．73和0．70;季节间小麦地与秋季各杂草群落间相似系数小于0．1。春、秋季弃耕地物种-相对多度分布曲线下降缓慢,常见种和偶见种多、相对多度分配分别占61．32％和47．09％;小麦地、玉米地、大豆地和葡萄地优势种突出。春季DA功能群占优势,小麦地高达81．06％;MP功能群较少,小麦地缺少MP。秋季玉米地和大豆地杂草功能群分布较均衡,葡萄地以DA和MP为主、分别为42．34％和42．64％;弃耕地MA、DA和MP平均,为33．63、31．07和30．25％。多样性指数为春、秋季弃耕地最高1．76和1．72,玉米、大豆地次之为1．55和1．52,春、秋葡萄地1．49、1．30,小麦地最低1．12。结论：不同土地利用方式杂草群落种群构成不同,功能群相对多度分配格局以免耕农田玉米地、大豆地和葡萄地杂草功能群分布均衡;功能群季节变化明显,趋势为MP上升,DA下降。不同土地利用方式土地多样性等级为小麦地〈葡萄地〈大豆地和玉米地〈弃耕地。     

Timing of disturbance and vegetation development: how sowing date affects the weed flora in spring‐sown crops

Abstract. The number of annual weeds were recorded in 752 field experiments in spring‐sown cereal crops conducted in Sweden 1972–1993. Two null hypotheses were tested regarding how the sowing date influenced the weed flora. 1. There is no relationship between the weed flora composition and sowing date. A pCCA (with geographic regions, crop species and soil types as covariables) clearly refuted this hypothesis. Hence, the composition of the weed flora varied depending on sowing date. 2. Species classified as summer annuals, winter annuals and germination generalists (that can germinate substantially in both spring and autumn) do not differ in their placement along the first ordination axis in the pCCA, i.e. according to sowing date. An ANOVA was unable to reject this hypothesis. Hence, germination syndrome classification did not explain the observed community differences related to sowing date. These results illustrate the importance of the date of disturbance for any secondary succession involving a seed bank and also the importance of annual dormancy cycles in seed banks.     

Comparative nesting and feeding ecology of skylarks Alauda arvensis on arable farmland in southern England with special reference to set-aside

1. A study of skylark Alauda arvensis L. breeding ecology in relation to crop type was carried out from April to August 1992 on arable land in southern England. Set-aside land was included in this comparative study.
2. Territory density averaged 0·15 ha⁻¹. It was 2–3 times higher in fields of set-aside and grass, especially permanent pasture, than in winter and spring-sown cereals.
3. Territory size was nearly twice as large in fields of winter cereals (4·5 ha) than in other crop types (2·5 ha). Where set-aside was present on one farm, territory size in set-aside (1·7 ha) was a third lower than in cereals and grass.
4. Nesting began in set-aside and permanent pasture in April and peaked in late May. Nesting was not detected in spring barley until late May and in silage grass until early June. The density of successful nests in set-aside fields was more than double that in any of the arable crop types.
5. Average clutch size at hatching was 3·91 eggs in fields of set-aside, over 15% higher than in silage grass (3·40) and in spring barley (3·27).
6. Fledging success did not differ according to crop type, but productivity, expressed as the number of fledglings produced per hectare, was 0·50 in set-aside, 0·13 in silage grass, and 0·21 in spring barley. Nests with chicks were not found in fields of winter cereals. The causes of chick death were thought to be predation in set-aside fields, farming practices in silage grass fields, and suspected starvation in spring cereals.
7. The potentially high nesting success of skylarks in set-aside implies that sympathetic set-aside management could play an important part in reversing its decline across the European Union.     

A survey of aphids and aphid parasitoids in cereal fields in Denmark, and the parasitoids' role in biological control

In 1996 and 1997 a field survey of the abundance and species composition of cereal aphid primary and secondary parasitoids in spring barley, winter wheat and durum wheat was conducted in Zealand, Denmark. The purpose was to create a better understanding of the mechanisms underlying aphid–parasitoid dynamics in the field. Such an understanding can be used when developing biological control methods in cereals. In both years aphid attacks in cereals began in late June and never exceeded the economic threshold. In 1996 the first aphids were found in wheat on 26 June; in 1997 the first aphids were found on 24 June on both crops. The highest densities reached in 1996 were an average of six aphids per shoot in winter wheat and one aphid per shoot in spring barley. In 1997 the highest densities reached were 11 aphids per shoot in winter wheat and four aphids per shoot in spring barley. The aphid population collapsed by the end of July to early August in 1996, but it collapsed by mid-July in 1997. The onset and peak of parasitization were delayed in comparison to aphid infestation. Parasitism was 20–60% by the end of the cropping season in spring barley, and 30–80% in winter wheat and durum wheat in 1996. In 1997 parasitism did not exceed 3–11% in barley and was less than 2% in one winter wheat field but more than 40% in the other winter wheat field sampled. In both years most parasitism was due to Aphidiidae (Hymenoptera). The two dominant species were Aphidius ervi Haliday and Aphidius rhopalosiphi De Stefani-Perez. Hyperparasitism began after primary parasitism and increased progressively during the cropping season. The two years were similar in many respects, including for species composition of aphids and parasitoids. The late start of the aphid infestation may have contributed to the high level of parasitization found in 1996, but in 1997 the aphid infestation period was so short that a parasitoid population did not have time to build up.     

Barley Yellow Dwarf Luteovirus (BYDV) Infectivity of Alate Aphid Vectors in Northeast Spain

Rhopalosiphum padi and Sitobion avenae alates were collected from colonised winter cereals and maize in N.E. Spain and fed on young wheat plants for 7–10 days in the glasshouse. Then, aphids were killed and the plants on which aphids reproduced were kept in the glasshouse for 30–40 days. ELISA of infested plants was made using polyclonal and monoclonal antisera against PAV-, RPV- and MAV-like isolates. In autumn and spring, MAV serotypes were transmitted by S. avenae and R. padi , mainly in mixed infections with PAV serotypes. This possibly explains the high frequency of MAV-like isolates and their previously recorded year-to-year stability in maize, grain and forage winter cereals and cereal volunteers. PAV-like isolates were rarely transmitted by S. avenae and its spread thus depends almost exclusively on R. padi. These results confirm the importance of forage cereals and cereal volunteers as virus sources for winter cereal infection in the autumn, and the latter as a source of BYDV for maize in spring.     

Interaction of local and landscape features in the conservation of Hungarian arable weed diversity

Question: How do local and landscape management contribute to weed diversity in Hungarian winter cereal fields? Location: Central Hungary. Methods: Vascular plants were sampled in 18 winter cereal fields along an intensification gradient according to nitrogen fertilization, in the first cereal rows (edge) and in the interior part of the fields. Weed species were divided into groups according to their residence time in Central Europe (native species, archaeophytes, neophytes) and nitrogen preference (low to medium, LMNP, and high, HNP species). The percentage of semi‐natural habitats was calculated in the 500 m radius circle. Effects of fertilizer use, transect position and semi‐natural habitats were estimated by general linear mixed models. Results: We recorded 149 weed species. Fertilizer had a negative impact on the species richness of archaeophytes and LMNP species, and on the cover of native weeds. There was greater species richness and weed cover at the edge of the fields than in the centre. A higher percentage of seminatural habitats around the arable fields resulted in greater total species richness, especially of archaeophytes and LMNP species. We found an interaction between the percentage of semi‐natural habitats and transect position for species richness of archaeophytes and LMNP species. Conclusions: Reduced use of fertilizers and a high percentage of semi‐natural habitats would support native and archaeophyte weed diversity even in winter cereal fields, while large amounts of fertilizer may promote invasion of neophytes. However, the beneficial effect of the semi‐natural habitats and greater species pool on the arable flora may prevail only in the crop edges.     

Landscape level processes driving carabid crop assemblage in dynamic farmlands

Landscape heterogeneity has been shown to be a major factor in the maintenance of biodiversity and associated services in agricultural landscapes. Farmlands are mosaics of fields with various crop types and farming practices. Crop phenology creates asynchrony between fields sown and harvested in different periods (winter vs. spring crops). The present study was conducted to examine the influence of such spatio-temporal heterogeneity on biodiversity, with the hypothesis that it would lead to spatio-temporal redistribution (shifting) of species. Species richness and activity-density of carabid beetles in winter cereal (winter) and maize (spring) crops were compared across 20 landscapes distributed along a double gradient of relative area and spatial configuration of winter and spring crops. Maize fields were sampled in spring and late summer for comparison over time. The response of carabid species richness to landscape heterogeneity was weak in spring, but maize field richness benefited from adjacencies with woody habitat, in late summer. In spring, increased length of interfaces between winter and spring crops lowered carabid activity-density in winter cereal fields, suggesting that maize fields acted as sinks. Interfaces between woody habitats and crops increased activity-density in both crop types. We found no evidence of spatio-temporal complementation, but different species benefited from winter cereals and maize in spring and late summer, increasing overall diversity. These findings confirm the role of adjacencies between woody and cultivated habitats in the conservation of abundant carabid assemblage in winter cereals and maize. We conclude that between-field population movement occurs, and advocate for better consideration of farmland heterogeneity in future research.     

Cereal weeds variation in middle Egypt: Role of crop family in weed composition

Cereals occupies a major part in the diet of humans globally, participating more to our daily protein and calorie intake than any other crop. The present study highlight the weed flora of cereal crops compared to other crops in middle Egypt and their distribution. Ninety-two weed species were recorded in the all studied crops, cereal and other crops; in the studied area belong to 67 genera and 20 families. Egyptian clover; showed the highest numbers of both weed species and genera followed by wheat, on contrast the lowest weed species and genera numbers were recorded associated with Solanaceous crops tomato and pepper. Wheat crops exhibited the highest number of weed species, among cereals, followed by maize crop, while the lowest weed species number was detected in barley crop. Chenopodium murale, Cynodon dactylon, Convolvulus arvensis and Malva parviflora were the most frequent species in winter cereals, while Echinochloa colona, P. oleraceae were the most frequent weeds in summer cereals. Chorological analysis of the recorded weed species showed that cosmopolitan elements showed the highest numbers in total weed flora Differences in weed species compositions were fundamentally influenced by seasonal priority. Based on TWINSPAN and Ward classifications, crop family showed slightly effect as a factor affecting weed composition.     

Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area

1. We report on a long-term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.
2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long-term mean.
3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.
4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.
5. The dominant zooplankton species in spring shifted in recent years from the large-bodied Daphnia galeata to the smaller D. cucullata . Cyclops kolensis , previously the only invertebrate predator during winter, decreased in abundance while C. vicinus , usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.
6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.     

Increasing habitat connectivity in agricultural landscapes as a weed management strategy reconciling ecology and agronomy

While studies have explored how habitat amount drives weed assemblages in agroecosystems, knowledge remains limited of the effects of habitat connectivity. The response-effect trait framework provides insights into the mechanisms underpinning the relationship between landscape structure and the taxonomic diversity and abundance of weed assemblages. This study evaluated how habitat connectivity and habitat amount affect weed diversity and abundance in winter cereal fields, and whether these effects are driven by the functional composition of weed assemblages. We sampled weeds in 27 winter cereal fields. We measured habitat connectivity and habitat amount provided by wooded, grassland and cropland elements. We selected five traits related to the dispersal, establishment, and competitive abilities of weed species likely to respond to landscape structure: seed number per plant, type of reproduction, seed dry mass, plant vegetative height and seed germination rate. The functional composition of weed assemblages was assessed using community weighted mean trait values. Weed diversity and abundance were used as proxies of weed management. The taxonomic approach did not reveal any effect of landscape structure on weed diversity and abundance. Only the grassland elements that contributed to habitat connectivity, and to a lesser extent to habitat amount, drove the functional composition of weed assemblages. High habitat amount favoured species with many seeds, while high habitat connectivity favoured species with fewer seeds, a higher ability to reproduce vegetatively and higher seed germination rates. In turn, higher seed germination rates increased weed evenness and reduced weed abundance. Some of these relationships were influenced by the presence of rare species. Overall, high connectivity provided by grassland elements increases weed evenness and reduces weed abundance by shaping weed functional composition. Our study suggests that land-use planning policies that enhance the connectivity provided by grassland elements could be considered as a weed management strategy reconciling ecology and agronomy.     

Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area

1. We report on a long-term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.
2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long-term mean.
3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.
4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.
5. The dominant zooplankton species in spring shifted in recent years from the large-bodied Daphnia galeata to the smaller D. cucullata . Cyclops kolensis , previously the only invertebrate predator during winter, decreased in abundance while C. vicinus , usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.
6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.     

Habitat selection by Skylarks Alauda arvensis wintering in Britain in 1997/98

The results of a national survey of wintering Skylarks Alauda arvensis undertaken by the British Trust for Ornithology (BTO) between November 1997 and February 1998 are reported here. Over three visits, volunteers counted Skylarks and mapped habitats in 541 1-km squares selected from the Skylark's winter range based on BTO Winter Atlas data and a stratified random sampling approach. Four landscape strata were defined from the Institute of Terrestrial Ecology landscape classification: arable, pastoral, marginal upland and saltmarsh. The survey counts underestimated Skylark abundance, but were good measures of relative abundance across habitat types. The two best predictors of Skylark presence–absence at the landscape scale were the availability of coastal and farmland habitats. Squares with saltmarsh had the highest densities and occupancy (80% of squares). At the patch scale crop stubbles, especially weedy cereal stubbles, were used significantly more than expected by chance. Oilseed rape was positively selected whereas cereal crops were used in proportion to availability and grazed grass was avoided. Skylarks avoided fields smaller than 2.5 ha and selected fields larger than 7.5 ha. We estimate that in midwinter there may be less than 1–2 ha of weedy cereal stubble per 1-km square. We recommend the retention of over-winter stubbles for the conservation of Skylarks and other farmland birds, and research on stubble management and effects on grain availability and arable weed regeneration on Skylark use.     

Effects of environmental factors on weed species composition of cereal and stubble fields in western Hungary

Multivariate analysis of data obtained from 184 cereal and stubble fields in low-input agricultural systems located in western Hungary was undertaken in order to asses environmental factors affecting weed species composition. For each variable, the gross and net effect on weed species composition was calculated. All variables considered in this study had a significant effect on weed species composition and explained 26.99% of the total variation. Most variation in species composition was explained by the aspect (cereal vs. stubble), followed by soil pH, mean annual precipitation, soil texture, mean annual temperature, and altitude. Separating the cereals and stubbles soil pH became the most important factor. Our results suggest that during the long vegetation period, cereal weed communities dominated by winter annuals are replaced by stubble-field weed communities dominated by summer annuals. This seasonal change may also have the same important effect on weed species composition as crop types.     

Farming for pests? Local and landscape-scale effects of grassland management on rabbit densities

In recent decades in the UK, there has been an increasing trend in numbers of the European wild rabbit, a significant agricultural pest typically associated with grassland habitats. However, the relationship between rabbit abundance and grassland management, in particular grazing, has not been sufficiently explained. We studied rabbit densities in seven pasture-dominated sites in north-east England between autumn and spring in two consecutive years, and used generalised linear mixed models and generalised additive models to explore relationships between habitat and management variables and rabbit abundance at local (field) and landscape scales. At the local scale high rabbit densities were significantly associated with small fields and the very short, homogeneous swards created by intensive sheep grazing during autumn and winter. At the landscape scale, high rabbit numbers were associated with sites with most field margins and a predator removal policy. Our results indicate that landscape management may play a central role in explaining rabbit abundance and distribution in grasslands. We suggest that current pasture management may create favourable conditions for high rabbit densities, and consequently boost numbers of this significant pest species.     

Winter decline of spiders and insects in spruce Picea abies and its relation to predation by birds

Insects and spiders were sampled on branches of spruce in a 5.5 km² area before and after each of six winters. Psocoptera, Aphidoidea and Lepidoptera larvae were the most common insects in autumn. In Feb–Mar only 1% remained, most of the decline occurring already early in the winter. Spiders were almost as common as Psocoptera in autumn but survived winter to 28–45%. Spiders therefore are potentially more important food for wintering birds than are insects. Through the first five winters there was a steady increase in density of small (but not large) spiders both in autumn (290%) and spring (390%). Spring densities of small but not large spiders were significantly correlated to autumn densities. Usually there was no added variability of spider abundance between trees and most of the variability was found within trees. In autumn spiders occurred at significantly higher densities in the lower half of the spruce trees than in the upper half. Much of the reduction of large spiders over winter is known to be caused by predation by birds. Over winter, this predation probably makes the distribution of spiders within trees more uniform. The autumn density of three tit species, the goldcrest and the treecreeper was significantly correlated with the density of large spiders at the same time, but not with small spiders (which they presumably do not eat). This might be caused by territorial behaviour being related to food density in autumn.     

Effects of different cultivation types on native and alien weed species richness and diversity in Moravia (Czech Republic)

Changes in weed species richness and beta-diversity are partly attributable to different types and intensity of disturbance and partly to broad-scale variation in environmental conditions. We compiled a data set of 434 vegetation plots of weed vegetation in root crop and cereal fields in Moravia (eastern Czech Republic) to compare the effects of environmental conditions and different disturbance regimes on species richness and beta-diversity. To detect changes in species richness, we related the variation in species richness to individual environmental conditions. To assess differences in beta-diversity between the vegetation of cereal and root crop fields, we used Whittaker's measure of beta-diversity. The relative importance of each environmental variable for the variation in species composition was evaluated using canonical correspondence analysis. All analyses were done for all vascular plant species and separately for native species, archaeophytes and neophytes. A comparison of weed vegetation of root crops and cereals showed a distinct dichotomy between these two types of weed vegetation. There was no significant difference in total species richness and native species richness; however, cereal fields were richer in archaeophytes and root crop fields were richer in neophytes. The beta-diversity of weed vegetation was higher in root crops. Environmental factors explained a significant part of the variability in richness of both natives and aliens. The richness of native species increased and beta-diversity decreased with increasing precipitation. The opposite relationship was found for archaeophytes, in both cereals and root crops. These results confirmed the importance of climatic factors and management practices for changes in weed species composition. They also showed a distinct pattern of species richness and beta-diversity of native and alien weed species.     

Seasonal variation in the abundance, biomass and biodiversity of earthworms in soils contaminated with metal emissions from a primary smelting works

1. Earthworms (Annelida: Oligochaeta) were sampled on four occasions (spring, summer, autumn and winter) at 14 sites along two transects from a primary lead/ zinc/cadmium smelting works at Avonmouth, UK.
2. Total abundance and biomass of earthworms decreased with proximity to the smelter. No worms were collected from the two sites closest to the factory (<0·6 km) and catches were significantly lower than controls at a further five sites (<3 km).
3. Seasonal composition of sampled communities differed only for summer with lower numbers of individuals and species collected at all sites. Reduced catches in the summer sample is a response to drought.
4. Species richness was lowest at sites close to the factory. For example, worms such as Aporrectodea caliginosa (Savigny) and Allolobophora chlorotica (Savigny) that were dominant at relatively clean sites further from the smelter are absent from the most contaminated soils.
5. Reduced species richness resulted in lower Shannon–Weiner diversity and higher Berger–Parker dominance. Multivariate cluster analysis for spring, summer and winter indicated that sites could be split into three groups based upon relative species composition. In autumn, two clusters were identified.
6. The absence of sensitive species from sites close to the smelting works supports the inclusion of earthworms as a key group in a terrestrial prediction and classification scheme for quantifying the effects of pollutants on soil biodiversity. However, sampling should be carried out in spring or autumn to obtain an accurate picture of community structure.     

The impact of plant associations on Macrosteles quadrilineatus management in carrots

Habitat diversification can influence the interactions of insects with plants and this can be used in agroecosystems for the management of pest populations. Plant diversification can be achieved through planting crops, such as trap crops, or by adjusting weed management. Aster leafhopper, Macrosteles quadrilineatus Forbes (Hemiptera: Cicadellidae), is a polyphagous species that uses cereals, vegetables, and weeds as host plants. The influence of weeds on M. quadrilineatus abundance was investigated experimentally in carrot [Daucus carota L. cv. Canada (Apiaceae)] field plots by adjusting the level of management of two groups of weeds (broadleaf and grass) and by comparing it to weed‐free plots. The preference of M. quadrilineatus for different cereal and weed species relative to carrots was tested in choice test assays. Habitat context influenced the abundance of M. quadrilineatus in the field experiments. The presence of border crops such as oat, rye, barley, wheat, and triticale did not significantly attract or repel this insect to carrot plots compared to the no‐border treatment. However, spelt‐bordered plots had 42% fewer M. quadrilineatus than three treatments, triticale, wheat, and barley, that had the highest insect abundance. The type of weed management affected M. quadrilineatus abundance in carrot plots, but not the frequency of herbicide application. Plots that had carrot growing with broadleaf‐weeds had about 59% fewer M. quadrilineatus compared with those growing with crabgrass or carrot alone. In the greenhouse choice tests, grasses (e.g., cereals) attracted and broadleaf‐weeds repelled M. quadrilineatus relative to carrots. In summary, carrot growers may be able to manage this pest by reducing the interaction of cereal cover crops with carrots and eliminating grassy weeds in commercial production fields.     

Are primary woody hosts ‘island refuges’ for host‐alternating aphids and important for colonization of local cereals?

Only few studies are available dealing with the relation between winter host density and spatial distribution and spring colonization of winter cereals by the host‐alternating cereal aphid species Rhopalosiphum padi and Metopolophium dirhodum. Large‐scale studies in climatically different agroecosystems in Germany from 2004 to 2006 revealed for R. padi and M. dirhodum larger spring/summer populations in landscapes with higher densities of winter hosts. A small‐scale study was performed in winter wheat fields adjacent to a large hedge with several typical winter hosts plants, bird cherry (Prunus padus) and wild rose species (Rosa spp.) to indentify distance effects (0–8, 8–24 and 24–60 m). Weekly measurements of aphid density between May to July showed significantly higher densities of R. padi compared with those of other aphids. Statistical analysis (Tukey–Kramer test and regression analyses) revealed significant gradients from the hedge to the field centre for R. padi and M. dirhodum. In comparative studies, winged R. padi from winter and adjacent summer hosts were genotyped using four microsatellite markers. The results showed that individuals from a certain winter host were not genetically similar with individuals from neighbouring summer hosts; it, therefore, seems that winter host clones did not significantly contribute to population built‐up in cereal fields over short distances. It could be concluded that on a regional scale, the density of sources for early migrants of R. padi is important for colonization intensity of surrounding summer hosts, but that the high local movement intensity and the relative small proportion of aphids that could be analysed in such tracking studies are blurring close spatial relations within short time periods.