农林复合系统中灌木篱墙对异色瓢虫种群分布的影响

以北京大兴农区农林复合系统为对象,围绕灌木篱墙(沙棘绿篱和杨树萌条带)上和麦田中的主要捕食性天敌——异色瓢虫对栖息地的选择趋向及灌木篱墙对异色瓢虫种群分布的影响进行了研究。结果表明:(1)小麦生长前期(返青期至抽穗期或扬花期)灌木篱墙上异色瓢虫种群密度是麦田的3.25—9.57倍,是异色瓢虫由越冬地向麦田过渡前的主要栖息地,是农林复合系统中异色瓢虫种群建立的"种库";(2)异色瓢虫对栖息生境有较强的选择性,明显趋向于蚜虫密集分布的生境,小麦生长前期趋向于灌木篱墙,小麦生后期(扬花期或灌浆期至完熟期)趋向于麦田,整个小麦生长期内异色瓢虫种群在不同生境斑块间存在明显的移动现象;(3)麦收后,邻近麦田的杨树萌条带上异色瓢虫种群密度相比于完熟期增加了42%,为异色瓢虫提供了重要的庇护场所。     

Aphis migration and the efficiency of the trapping method

Reproducible results were obtained when adhesive traps for aphides were placed at the same height in different parts of a potato field. The total catches in different localities in different seasons can therefore justifiably be compared. During the summer dispersal flights, different species flew at different heights, so traps at one height only are not suitable for comparing the relative abundance of different species. There was less variation in numbers caught on traps at 3–4 ft. above the ground than on traps at 5–6 ft. or at ground-level.
During the first fortnight of July an average of 200 aphides, 1.6% of which were Myzus persicae , was caught on traps in the position of potato plants. Most of these were not potato aphides, but it is suggested that some of them might act as vectors of potato viruses. The number of aphides caught was roughly proportional to the volume of free air space around the traps, and as the foliage increased in density the numbers caught on lower traps decreased in proportion.
Wind-speed records within and above the crop are discussed and it is shown that conditions are often suitable for voluntary aphis flight in and near the crop on relatively windy days. Records of catches on the half-traps facing the wind and on the other halves showed that voluntary flight decreased with increasing height.
Brilliant yellow traps, coated with adhesive grease, caught more aphides than white traps, which in turn caught more than black.     

棉花不同栽培方式对卵形异绒螨种群密度的影响

卵形异绒螨是棉蚜的一种外寄生性天敌,研究结果表明,呋喃丹和甲拌磷处理的种子中卵形异绒螨种群波动趋势,与非杀虫剂各种子处理田一致,药剂处理田的天敌数量与非药剂处理田无显著差异（Ｐ〉０．０５）,单作露地棉田的螨量高于棉,麦套种和地膜覆盖田;卵形异绒螨随着翅蚜向露地棉田在迁移量为９０．７头／ｍ＾２．２４ｈ向覆盖田的迁移量为３６．０头／ｍ＾２．２４ｈ随着棉田连作时间的延长,卵形异绒螨的种群密度呈逐渐增加的     

The behaviour of some naturally occurring strains of potato virus Y

Potato virus Y was obtained from field crops of potatoes in many strains which differed widely in virulence and caused diseases in the variety Majestic ranging from severe leaf-drop streak to mild mosaic. The symptoms caused by these strains in seven potato varieties and tobacco are described and compared with those caused by the serologically related potato virus C. No changes were noted in the behaviour of any of the strains over three years, during which they were transmitted to many different plants.
Potato virus C was not transmitted by Myzus persicae , the most efficient vector of other strains of virus Y. Nor was virus C transmitted by eleven other species of aphides, eight of which transmitted virus Y. The efficiency with which different species acted as vectors of virus Y varied greatly, and it is suggested that in some species only occasional individuals can transmit.
Possible mechanisms for the evolution of viruses C and Y are indicated, and the effects of changes in virus, vector, and host on the prevalence of insect-transmitted viruses are discussed.     

Summer bird abundance and distribution on set-aside fields on intensive arable farms in England

The abundance and distribution of breeding birds were compared on paired fields comprising one set-aside field and one crop field, on 11 intensive arable farms in eastern and western England. A single observer made four visits to all set-aside and crop fields between April and July and recorded all birds seen during standardised counts and transects.
Rotational and non-rotational set-aside supported higher densities and more species of birds than fields of wheat, brassicas, root crops and seed rye. These differences in density, between set-aside and crops, were evident across a suit of species including waders, gamebirds, pigeons and passerines and were particularly marked on rotational set-aside. The majority of species recorded in fields away from boundaries would have been feeding rather than nesting there and higher bird densities on set-aside compared with adjacent arable crops probably reflects greater food abundance in the former.
The study is the first to demonstrate a clear habitat preference for set-aside by a wide range of bird species throughout the breeding season and it allows a number of recommendations to be made concerning the development of cost-effective agri-environment measures. The fact that the majority of birds utilised the outer 5 m, or in some cases 20 m, margin of the field suggests that many of the benefits of whole field set-aside may be derived from marginal strips. A slight, but not significant preference for rotational over non-rotational set-aside suggest such margins should be managed to maintain a patchy, relatively diverse sward of arable plants. A key feature of set-aside is the scale at which it has been incorporated into the arable landscape. Agri-enviromental schemes will only provide similar national benefits if they are implemented on a wide scale in such as way as to promote high uptake by farmers.     

Varietal differences in susceptibility to potato virus Y

In addition to giving different kinds of symptoms when infected with potato virus Y , individual potato varieties also differ in their susceptibility to infection, in the concentration of virus attained in their sap, and in their efficiency as sources of virus for aphides. Their relative susceptibility in the open when exposed to equal chances of infection is correlated with the ease with which they become infected when colonized with infective aphides, and can be assessed from tests made under glass. Methods for making such tests are described; these need few tubers and give reproducible results. It is considered that they could be applied in studying the inheritance of this type of resistance and to test the behaviour of new seedlings. The American variety Katahdin was the most resistant of those tested, but there were significant differences between commercial British varieties.
In the open, all varieties were equally colonized by aphides and resistance to infection with virus Y was not correlated with resistance to leaf roll.     

Increasing the effectiveness of spring trap crops for Leptinotarsa decemlineata

Insecticide resistance problems have increased interest in trap crops as a cultural control strategy for overwintered Colorado potato beetle adults, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae). Growers in the north central United States have noticed and treated concentrations of adults at the edge of some of their potato fields each spring. Based on sampling in commercial potato fields over a 2-year period, early planted fields that are adjacent to the previous year's potato crop are most likely to have concentrations of adults at the field edge. Frequency of fields with significantly more adults at the edges than in the center sections as well as adult population density in the center sections of fields declined with both distance from the previous potato field and later planting date. The effects of both physical and chemical barriers to movement into potato fields from the field edges were studied in small plot trials and at the edges of commercial potato fields. In small plot trials, physical barriers had a greater impact than chemical barriers on adult beetle movement from a potato trap crop to the protected potatoes beyond the barrier. Barrier treatments reduced beetle numbers in and just beyond the barrier in commercial fields, but the effects were localized and no significant reduction of beetles was observed further into the field. Beetle flight was hypothesized to be responsible for the localized effects of barrier treatments and the lack of edge concentrations in later planted and more distantly rotated fields. In field studies, larger potato plants attracted more colonizing potato beetles than smaller plants. Attracting Colorado potato beetles to trap crops containing potato plants that were larger than those in the remainder of the field, however, provided no significant reduction of beetles in the remainder of the field. We found little opportunity to reduce beetle populations with trap crops at the edges of potato fields without controlling the adults in the trap crop itself. Growers can exploit naturally occurring concentrations of adults at the edges of early and adjacent potato plantings if they are prepared to monitor and regularly treat the field edges.     

大田环境下转Bt基因玉米对土壤酶活性的影响

在大田自然条件下,比较研究了转Bt基因玉米和非转基因亲本玉米在种植和秸秆分解时对土壤酶活性影响的差异。结果表明,与亲本非转基因玉米相比,在各生育期内种植转Bt玉米对土壤蛋白酶和土壤脲酶活性均没有显著影响;在喇叭口期和抽雄期,土壤蔗糖酶和土壤酸性磷酸酶活性显著提高。在秸秆还田后,两种玉米秸秆对土壤酸性磷酸酶活性的影响没有显著差异,但使用转Bt玉米秸秆的土壤蔗糖酶、土壤脲酶和土壤蛋白酶的活性则有显著提高。与亲本玉米相比,在所有观测期内,种植Bt玉米及秸秆还田对土壤酶活性的影响,在影响的幅度及趋势上随玉米生育期和土壤酶种类的不同而产生差异,但没有观测到显著不利影响;商业化Bt玉米的环境释放仍有待长期定位观测和评价。     

Migration patterns and functional groups of spiders in a desert agroecosystem

Abstract 1. Arthropods living in annual crops suffer mortality caused by agricultural practices. Therefore, migration from surrounding habitats is crucial to maintain populations of natural enemies of insect pests in crops. In desert agroecosystems there is a pronounced contrast between managed and unmanaged habitats, where irrigated and fertilised crops are islands of productivity in an arid matrix. This contrast could either enhance or inhibit movement of natural enemies between the landscape components. 2. The importance of the surrounding arid habitats as a source for spiders in crops was examined in the Negev desert of Israel. Spiders were sampled in both arid natural habitat and adjacent wheat fields using pitfall traps and visual searching. In addition, spiders in wheat fields were sampled throughout the winter cropping season using emergence traps at increasing distances from the field edge. Stationary and movable emergence traps were used to distinguish between residents and migrant species. 3. The spider assemblage in the wheat was dominated by three families: Linyphiidae, Theridiidae, and Gnaphosidae. Spider sampling in both natural arid habitat and adjacent wheat fields enabled four functional groups to be recognised that differed in habitat preference, movement patterns, and population dynamics. Thirty‐three per cent of collected individuals were classified as crop residents whereas more than 50% were classified as migrants from the surrounding habitats. These findings suggest that the surrounding habitats influence spider assemblage composition in the fields, in spite of the marked contrast in habitat structure and productivity. 4. Spider assemblages in the wheat fields were dominated by migrant species arriving from the surrounding arid habitats. Migrant spiders inhabited the crop throughout the cropping season. The combined contribution of resident and migrant functional groups may act to prevent insect pest outbreaks in this desert agroecosystem.     

Dry rot of potato Fusarium caeruleum (Lib.) Sacc.; effect of planting infected and contaminated sets on plant establishment

The effect on plant establishment of planting infected and contaminated sets of susceptible varieties has been studied in field trials from 1942 to 1945.
Healthy whole sets, and whole sets inoculated internally 3 days before planting, yielded good stands, whilst whole sets with obvious dry-rot lesions present at planting time produced gappy crops.
Healthy cut sets gave satisfactory stands except in one test with Doon Star, whilst sets cut with a contaminated knife at planting time yielded only a few misses in 1943 but many in the unfavourable 1944 season and in 1945.     

Small wild bee abundance declines with distance into strawberry crops regardless of field margin habitat

The preservation of pollinator habitat on croplands in the form of hedgerows, wildflower strips, and natural and semi-natural areas can help maintain and enhance wild bee populations in agricultural landscapes. However, there have been few comparisons of the effectiveness of different types of field-margin pollinator habitat in maintaining bee diversity and pollination of the focal crops. We compared wild bee abundance, species richness and community composition between strawberry crops bordered by hedgerows, and those bordered by larger expanses of natural land (forests). Strawberry is an ideal crop in which to investigate pollinator export from field margins as the rows are covered with straw, which reduces habitat for ground-nesting bees within the crop; thus, most wild pollinators need to enter the crop from the margins. We sampled bees in six strawberry fields with hedgerow margins and six strawberry fields with forested margins of at least 200 m in length, using a paired design. We examined strawberry pollen deposition at regular intervals into the fields, and the magnitude of pollinator export from the field margins towards the centre of the crops. We found that bees as a group were no more species-rich or abundant in crops bordered by forests than in crops bordered by hedgerows, although large-bodied bees were more abundant in the former than the latter. Regardless of field-margin type, we found that small wild bee abundance declined significantly from the edge to the centre of the crop, but honey bee (Apis mellifera L.) and large-bodied bee abundance did not. Strawberry pollen deposition also did not decline with distance into the crop. Although previous work indicates that small wild bees are more effective (yield-increasing) pollinators of strawberry on a per-visit basis, their limited foraging ranges suggest they may only pollinate areas near the crop margins, given typical field sizes in our area.     

罗汉果疱叶丛枝病的媒介昆虫和防治途径的研究

试验结果指出:棉蚜Aphis gossypii Glov.是罗汉果Siraitia grosvneri(Swingle)Jeffrey.疱叶丛枝病的媒介昆虫。有翅蚜和无翅蚜都有传毒力:传毒习性的研究结果指出:每苗接虫三头或使之吸食15分钟以上,就足以使健苗发病。 由于媒介昆虫自然传播的主导因素.所以理论上和实践上都指出与病区隔离种植实生苗,是解决罗汉果疱叶丛枝病的根本措施之一。     

Evolution of resistance to transgenic crops: interactions between insect movement and field distribution

The refuge strategy is designed to delay evolution of pest resistance to transgenic crops producing Bacillus thuringiensis Berliner (Bt) toxins. Movement of insects between Bt crops and refuges of non-Bt crops is essential for the refuge strategy because it increases chances that resistant adults mate with susceptible adults from refuges. Conclusions about optimal levels of movement for delaying resistance are not consistent among previous modeling studies. To clarify the effects of movement on resistance evolution, we analyzed simulations of a spatially explicit model based partly on the interaction of pink bollworm, Pectinophora gossypiella (Saunders), with Bt cotton. We examined resistance evolution as a function of insect movement under 12 sets of assumptions about the relative abundance of Bt cotton (50 and 75%), temporal distribution of Bt cotton and refuge fields (fixed, partial rotation, and full rotation), and spatial distribution of fields (random and uniform). The results show that interactions among the relative abundance and distribution of refuges and Bt cotton fields can alter the effects of movement on resistance evolution. The results also suggest that differences in conclusions among previous studies can be explained by differences in assumptions about the relative abundance and distribution of refuges and Bt crop fields. With fixed field locations and all Bt cotton fields adjacent to at least one refuge, resistance evolved slowest with low movement. However, low movement and fixed field locations favored rapid resistance evolution when some Bt crop fields were isolated from refuges. When refuges and Bt cotton fields were rotated to the opposite crop type each year, resistance evolved fastest with low movement. Nonrecessive inheritance of resistance caused rapid resistanceevolution regardless of movement rate. Confirming previous reports, results described here show that resistance can be delayed effectively by fixing field locations and distributing refuges uniformly to ensure that Bt crop fields are not isolated from refuges. However, rotating fields provided better insect control and reduced the need for insecticide sprays.     

Slow arbuscular mycorrhizal colonisation of field-grown cotton caused by environmental conditions in the soil

 Slow arbuscular mycorrhizal colonisation is characteristic of a growth disorder of cotton occurring in crops in northern New South Wales, Australia. To determine whether or not slow colonisation is caused by poor survival of mycorrhizal fungi between crops, we examined colonisation of cotton in field crops and in a series of pot bioassays. Cotton roots were sampled at sites with or without severe symptoms of the growth disorder in each of three fields in 1991 and two fields in 1993. The bioassays were at intervals over the winter fallow prior to the crops in both years. In each bioassay, soil was collected from the field sites and sown with cotton in pots in a controlled environment cabinet. Colonisation was assessed at 14, 28 and 42 days after sowing. In the bioassay series, colonisation at 14 days, which was representative of primary infections of roots and hence propagule density in soil, tended to decline over the winter fallow. In contrast, colonisation at 42 days, which included secondary spread of infection, first declined and then returned to its original level or higher. In the field, plants affected by the growth disorder were colonised slowly, while healthy plants were colonised rapidly. In the bioassays, however, colonisation in the soil from sites with the growth disorder equalled or surpassed that in soil from sites with healthier cotton. Thus, the slow colonisation and growth of field-grown cotton did not result from a lack of mycorrhizal inoculum and was most likely caused by soil factors. Accepted: 21 August 1998     

Approaches to reconstruction of early Celtic land-use in the cent ral Neckar region in southwestern Germany

In four early Celtic settlements in the central Neckar region of Baden-Württemberg (Germany), 250 archaeobotanical samples were collected and studied for their plant macrofossils.Hordeum vulgare L. (hulled barley) andTrilicum spella L. (spelt wheat) could be recognized as the main crops, as well asPanicum miliaceum L. (millet) in some places. Legumes andLinum usitatissimum L. (flax) were important crops. Typical field weeds dominated the wild plant remains, but some present-day grassland taxa were abundantly and frequently found. The analysis of the data set of finds of the cereal remains, field weeds and grassland plants was done by Correspondence Analysis, but no significant differences between the various groups were found. Samples dominated by remains of grassland taxa, which could indicate that there were hay meadows, were absent. Consideration of plant macrofossil results as well as archaeological, osteological and pollen analytical data shows that there is likely to have been a land management system of arable fields and grassland. The densely settled fertile central Neckar region could therefore have been intensively utilised, using all available resources. Permanent grasslands in the form of pasture on river floodplains and on dry soils were certainly present. Hay meadows, on the other hand, were not identified. Cultivated plants such asFicus carica L. (fig) andVicia ervilia (L.) Willd. (bitter vetch) as well as some field weeds suggest connections with the Mediterranean lands.     

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.     

Influence of dispersal from almonds on the population dynamics and acaricide resistance frequencies of spider mites infesting neighboring cotton

Neighboring almond and cotton fields were sampled for spider mites in four locations in the San Joaquin Valley of California. The dominant species in the almonds wasTetranychus pacificus McGregor. In three cotton sites.T. pacificus was present in significantly higher densities near the almonds on at least one sampling date. In contrast.T. urticae Koch andT. turkestani Ugarov & Nikolski were equally abundant across the cotton fields. Almonds appeared to act as a continuous early-season source ofT. pacificus for cotton, with peaks in aerial dispersal from almonds occurring due to overcrowding, plant water stress, and applications of repellent acaricides. Cotton, which experienced little water stress, supported very high densities of spider mites and so acted primarily as a sink for spider-mite dispersal from almonds and other field crops throughout the growth-season. The frequencies of resistance expressed byT. pacificus andT. urticae were similar between neighboring crops, even if the acaricide had been registered for use only in almonds (cyhexatin) or cotton (dicofol). Thus, longterm acaricide selection and movement of spider mites between the two crops resulted in similar proportions of resistant individuals. In these study sites, large-scale dispersal ofT. pacificus from almonds rarely directly affected acaricide efficacy in cotton, because resistance frequencies were similar for spider mites from the two crops and because acaricide applications were usually made in cotton after dispersal from almonds was completed. In two cotton sites, field selection with dicofol was reversed by subsequent immigration of spider mites from neighboring field crops.     

Field preference of Greylag geese <Emphasis Type="Italic">Anser anser</Emphasis> during the breeding season

Few studies address food preference of geese on agricultural land (utilization related to availability) and only a handful so for the breeding season. We studied Greylag geese Anser anser during the breeding season in an intensively farmed area in southern Sweden. Few of 22 available field types were truly preferred. Pastureland was the most consistently preferred, by goslings (with parents) as well as by non-breeders. In some sampling periods, goslings also preferred grazed hay, ley, and carrot fields. Non-breeders exploited a greater variety of crops/fields, feeding also on barley, fallow, grazed hay, lettuce, oats, potatoes, and carrots. Most of these crops were preferred on at least one sampling occasion, except for fallow, grazed hay, and wheat, which were always used less than expected from availability. GLMs revealed that goslings rested more than they fed and preferred shorter vegetation before higher. Moreover, goslings occurred in higher densities in younger age classes than in older and preferred nearshore areas. In contrast, density of non-breeders was only related to field type and sampling occasion (higher densities as the season progressed). The maximum number of broods observed (106) implies a breeding success of 34% based on 311 active nests earlier in the season. Brood size decreased from 3.5 to 2.1 during the study period. Our study shows that goose management during the breeding season should consider goslings and their parents separately from non-breeders, and it implies little potential conflict between Greylag geese and agriculture during the breeding period.     

Changes in Organic Carbon and Trace Elements in the Soil of Willow Short-Rotation Coppice Plantations

Short rotation coppice (SRC) is a biomass production system for energy usually grown on former agricultural land with fast-growing tree species. In Sweden, willow SRC has been grown since the late 1980s. SRC on arable soils may induce changes in some soil quality parameters due to differences in crop characteristics and management practices. In this study, pH, organic carbon (C), and trace element concentrations in the soil of 14 long-term (10–20 years) commercial willow SRC fields in Sweden were compared with those in adjacent, conventionally managed arable soils. The results showed that organic C concentrations in the topsoil and subsoil of SRC fields were, on average, significantly higher (9 % in topsoil, 27 % in subsoil) than in the reference fields. When comparisons were made only for the ten sites where the reference field had a crop rotation dominated by cereal crops, the corresponding figures were 10 % and 22 %. The average concentration of cadmium (Cd), which is considered the most hazardous trace element for human health in the food chain, was 12 % lower in the topsoil of SRC fields than in the reference fields. In the corresponding comparison of subsoils, no such difference was found. For chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn), there were no significant differences in concentrations between SRC fields and the reference fields in either topsoil or subsoil. Negligible differences in pH in the same comparisons were found.