Aphid and episodic O3 injury in arugula plants (Eruca sativa Mill) grown in open-top field chambers

Aphid attacks and tropospheric ozone (O₃) cause stress and considerable damage in both wild and cultivated plants. Induced defense responses to aphid attacks and O₃ exposure share signaling pathways with common points. We investigated the plant–aphid interaction under O₃ exposure using open-top O₃ chambers. Ozone leaf injury was lower in aphid-infested plants than in aphid-free plants, although herbivore damage was not evident. Aphid population growth was strongly affected by previous exposure to O₃ but no direct effect of O₃ was observed. The possibility that during O₃ episodes, herbivores may reduce O₃ damage on host plants and that the offspring of the exposed aphids have lower population growth rates opens new and intriguing questions about potential effects of future increased tropospheric O₃ levels on plant–insect interactions.     

Diversity of cereal aphid parasitoids in simple and complex landscapes

Structurally complex landscapes may enhance local species richness and interactions, which is possibly due to a higher species pool in complex landscapes. This hypothesis was tested using cereal aphid parasitoids (Hymenoptera, Aphidiidae) by comparing 12 winter wheat fields in structurally complex landscapes (>50% semi-natural habitats; n = 6) and structurally simple landscapes dominated by agricultural lands (>80% arable land; n = 6). Surprisingly, landscape structural complexity had no effect on aphid parasitoid species diversity. In complex landscapes 12 and in simple landscapes 11 species were found; 9 species occurred in both landscape types. Hence, arable fields in high-intensity agricultural landscapes with little non-crop area can support a similar diversity of cereal aphid parasitoids as structurally complex landscapes. This finding suggests that cereal aphid parasitoids may find necessary resources even in simple landscapes, making generalisations concerning the relationship between landscape composition and biodiversity in arable fields difficult.     

Population growth of the blackmargined aphid on pecan in the field

Caged populations of Monellia caryella (Fitch) were observed to condition pecan leaves throughout the season resulting in the leaves being unsuitable for subsequent colonization. Aphid populations were greatest (peak of 70 aphids/leaf) and occurred for a longer period (25 days) compared to late season activity (peak of 37 aphids/leaf, lasting 11 days) before conditioning occurred in closed cages. Intrinsic rates of increase per day or per degree-day declined during the season. Population growth was best described using an exponential increase equation compared to a logistic equation. These results indicated that as pecan leaves aged they were a poorer substrate for M. caryella and more easily made unsuitable for subsequent colonization.     

Post-dispersal weed seed predation by avian and non-avian predators

Seed predation by avian and non-avian predators was quantified in the boundaries and cropped areas of cereal fields by presenting known quantities of seed with and without exclusion cages. Predator encounter-rates with the dishes exceeded 99%. Birds removed on average 6.7% seed from the dishes during the seven-day trials compared to 51% by non-avian predators. A comparison was made of the causal factors responsible for predation of Avena fatua, Chenopodium album and Cirsium arvense seeds. A. fatua seeds were preyed most heavily by both avian and non-avian predators. Seed removal by birds was greater in the cropped area than in the field boundary, non-avian predators being generally more active in the field boundary. Seed predation by birds was greater in spring than in any other season, whilst losses to other animals were greater during autumn and winter. Although, birds were not the main seed predators in cereal fields, they may contribute to weed seed depletion, of relevance to reduced-input farming systems where herbicides use is restricted.     

Winter diet of reed bunting Emberiza schoeniclus in fallow and stubble fields

An analysis of droppings collected in winter on unused fields in SW Poland (fallow, stubble of root crop, vegetable and cereal) showed that the base of the reed bunting Emberiza schoeniclus diet were seeds of annual weed species: Chenopodium album (74.06% of all recorded seed species), Amaranthus retroflexus (16.05%), Setaria viridis (9.50%), Stellaria media (0.21%), Fumaria officinalis (0.01%). The share of dominant weed species in the diet of reed bunting wintering on particular types of fields varied markedly. In the droppings from fallows and cereal stubbles, C. album clearly dominated (respectively, 88.60 and 66.12%). The highest proportion of A. retroflexus and S. viridis was detected in the diet of birds staying on root crop stubbles (respectively, 45.56 and 23.90%). The most diverse food composition was found in the case of birds feeding on root crops and the least diverse on fallows.     

Habitat quality of wildflower strips for common voles (Microtus arvalis) and its relevance for agriculture

Ecological compensation areas have been widely promoted in agriculture in the last decade. Besides their positive effects on biological diversity they also bear a risk of sheltering potential pest species such as common voles (Microtus arvalis). To assess the influence of wildflower strips on the spatio-temporal behavior of voles and their impact on adjacent crop fields, a common vole population living in a wildflower strip was monitored from May to October 2000 and from March to September 2001. A new system for automatic radio tracking was used which allowed tracking at 1 min intervals and up to 1000 bearings per vole per day. Voles showed small home ranges with a median size of 125 m² (minimum convex polygon) and 30 m² (Kernel), respectively. Home ranges were stable with a median overlap of 90% for consecutive days, were almost exclusively within the wildflower strip and contained several core areas per range. A polyphasic activity pattern with a phase length of 1.7 h was found during summer with a trend towards diurnal activity. Overall wildflower strips were high-quality habitats for voles and sustained high population densities without increased risk of voles dispersing into adjacent fields.     

环境激素氯氰菊酯对萼花臂尾轮虫繁殖的影响

以2 d种群增长率为指标研究了环境抗雄激素氯氰菊酯对萼花臂尾轮虫的急性毒性;以3 d种群动态参数(种群增长率、混交率、混交雌体受精率和携卵雌体/非携卵雌体)、7 d休眠卵产量和休眠卵孵化率为指标研究了低剂量氯氰菊酯(0.001～0.316 mg.L-1)对萼花臂尾轮虫繁殖的影响;以2 d种群参数分析了在氯氰菊酯中形成休眠卵孵化后的生长性能;以3 d种群参数为指标分析了母体暴露氯氰菊酯,对其后代繁殖的影响.结果表明氯氰菊酯浓度对数与种群增长率呈直线负相关.氯氰菊酯半数效应浓度(EC50)、最低可观察效应浓度(LOEC)和无可观察效应浓度(NOEC)分别为14.22、10和3.16mg.L-1;0.0316 mg.L-1氯氰菊酯组7 d休眠卵产量较对照组下降了41.23%,休眠卵孵化率亦较对照组显著下降;氯氰菊酯试验组中形成的休眠卵孵化后的种群增长率和混交率显著下降;萼花臂尾轮虫母体暴露0.316 mg.L-1氯氰菊酯其后代种群增长率比对照下降了15.96%.试验表明,萼花臂尾轮虫2 d种群增长率对氯氰菊酯较不敏感;低剂量氯氰菊酯可降低休眠卵产量、休眠卵孵化率及孵化后种群增长率,从而减少萼花臂尾轮虫后代早期对种群增长的贡献.     

Assessing the bioremediation potential of arsenic tolerant bacterial strains in rice rhizosphere interface

The arsenic tolerant bacterial strains Staphylococcus arlettae(NBRIEAG-6), Staphylococcus sp.(NBRIEAG-8) and Brevibacillus sp.(NBRIEAG-9) were tested for their roles in enhancing plant growth and induction of stress-related enzymes in rice(Oryza sativa L. cv. NDR-359) plants at two different concentrations, 30 and 15 mg/kg of As(V) and As(III), respectively. An experiment was conducted to test the effect of these strains on plant growth promotion and arsenic uptake. We found 30%–40% reduction in total As uptake in bacteria-inoculated plants, with increased plant growth parameters compared to non-inoculated plants. Moreover, the bacteria-inoculated plants showed reduced activity of total glutathione(GSH) and glutathione reductase(GR) compared to their respective controls, which suggests the bacteria-mediated reduction of oxidative stress in plants. Thus, these strains were found to be beneficial in terms of the biochemical and physiological status of the plants under arsenic stress conditions.Furthermore, one-way ANOVA and principal component analysis(PCA) on enzymatic and non-enzymatic assays also revealed clear variations. The results support the distinction between control and treatments in both shoots and roots. Therefore, this study demonstrates the potential of rhizobacteria in alleviating arsenic stress in rice plants.     

Potential for biological control of field bindweed in California's coastal vineyards

The possibility of using biological control against field bindweed, Convolvulus arvensis L., was studied in four vineyards along the California coast. Field bindweed is a dominant member of the weed community and the principal plant pest in these vineyards. There is considerable insect and mite damage to its foliage during late summer and autumn, but the stress this places on the weed is unknown. The most significant natural enemies of field bindweed are defoliating caterpillars, Bedellia somnulentella Zeller, Chaetocnema confinis Crotch, and spider mites. Non of the natural enemies present appeared to be suitable as biological control agents. However, some arthropods, such as Noctuelia floralis (Huebner), associated with field bindweed in Mediterranean Europe and Pakistan, could be useful in the California grape agroecosystem, once cleared for importation and release in North America. Others, unsuitable to release in California because of feeding on closely related native plants, may be of value in other parts of the world where no such conflicts of interest exist. It would be feasible to use biological control against field bindweed in California's coastal vineyards and, perhaps, also in orchards under present systems of cultivation. Its effectiveness could be enhanced by certain changes in growing practices, particularly the acceptance of some weed growth, and by changes in existing pest controls. Biological control of field bindweed should be considered in the development of pest management programs for such crops in California and wherever this plant is a serious pest.     

Tracking parasitoids with the stable isotope 44Ca in agroecosystems

Habitat management influences spatial and temporal distribution of parasitoids in farmland. The current work evaluates, for the first time, the potential of a novel marking technique using a calcium stable isotope (⁴⁴Ca) under field conditions. In two subsequent trials, ⁴⁴Ca-enriched Cotesia glomerata parasitoids were released into an organically managed cabbage field in a region known to harbor natural populations of this species. The trap plants infested with Pieris brassicae host larvae were distributed in the trial areas and collected 3 days after parasitoid release. Parasitism by released wasps was determined through calcium isotope analysis of the recovered caterpillars using inductively coupled plasma mass spectrometry (ICPMS). The spatial habitat use by female parasitoids was determined based on marked caterpillars on the trap plants. Both trials yielded relatively consistent results, showing that C. glomerata females dispersed over at least 50 m within 3 days. The total proportion of caterpillars parasitized by the marked wasps amounted to 32.4 and 24.4%, respectively, with no statistically significant difference. The potential of this approach for field investigations on habitat management and biological control is discussed.     

The selection of management strategies for controlling nematodes in cereals

Several genera and species of plant-parasitic nematodes cause losses in grain yield in cereals; some are of relatively minor importance (e.g. Anguina tritici (Steinbuch) Chitwood, the cause of “ear cockle” in wheat), while others such as the cereal cyst nematode (CCN) (Heterodera avenae Woll.) have a wide geographic distribution, infest extensive areas, and may cause losses valued at millions of dollars. Some of these nematodes are difficult to control because the measures that might be used are uneconomic to apply or are impractical. The control of CCN, however, can be achieved, and several successful strategies have been developed in parts of Europe and in Australia. The various measures available to Australian cereal growers include: crop rotation, resistant cultivars, manipulation of sowing dates, use of nematicides, and reduced cultivation. The selection of an appropriate management strategy for the control of CCN is influenced by factors such as: climate, cereal species grown, yield potential, rotations practised and the availability of alternative crops, pathotype present, farm size, availability of resistant cultivars, nematicides registered, and the availability of suitable equipment for their application.     

Nutrients regeneration pathway, release potential, transformation pattern and algal utilization strategies jointly drove cyanobacterial growth and their succession

In order to better understand the contribution of nutrients regeneration pathway, release potential and transformation pattern to cyanobacterial growth and succession, 7 sampling sites in Lake Chaohu with different bloom degree were studied every two months from February to November 2018. The carbon, nitrogen (N) and phosphorus (P) forms or fractions in surface, interstitial water and sediments as well as extracellular enzymatic activities, P sorption, specific microbial abundance and community composition in sediments were analyzed. P regeneration pathway was dominated by iron-bound P desorption and phosphorus-solubilizing bacteria solubilization in severe-bloom and slight-bloom area respectively, which both resulted in high soluble reactive phosphorus (SRP) accumulation in interstitial water. However, in severe-bloom area, higher P release potential caused the strong P release and algal growth, compared to slight-bloom area. In spring, P limitation and N selective assimilation of Dolichospermum facilitated nitrate accumulation in surface water, which provided enough N source for the initiation of Microcystis bloom. In summer, the accumulated organic N in Dolichospermum cells during its bloom was re-mineralized as ammonium to replenish N source for the sustainable development of Microcystis bloom. Furthermore, SRP continuous release led to the replacement of Dolichospermum by Microcystis with the advantage of P quick utilization, transport and storage. Taken together, the succession from Dolichospermum to Microcystis was due to both the different forms of N and P in water column mediated by different regeneration and transformation pathways as well as release potential, and algal N and P utilization strategies.     

缓控释肥深施对黏性土壤麦田氮素去向的影响

黏性土壤严重影响土壤水肥运移.采取适宜的农艺措施优化土壤无机氮分布,减少该类型土壤的氮素损失是农业绿色可持续发展的关键.为明确缓控释肥种肥深施对黏性土壤麦田氮素损失的影响,选择常规化肥(CN)和缓控释肥(RCU)这2种类型肥料,采用撒播撒施(B)和机械化条播深施(D),研究了缓控释肥种肥深施对黏性土壤小麦产量、季节麦田氮素径流流失、氨挥发和N₂O排放的影响;并分析了其耕层土壤的无机氮时空分布特征.结果表明,相同肥料类型下,D处理的小麦产量显著高于B处理;而相同施肥方式下,RCU处理的产量显著高于CN处理.D-RCU处理的小麦产量最高,达6.97 t·hm^-2.季节径流和氨挥发氮损失量高于N₂O形态的氮损失,且不同损失途径对肥料类型和施肥方式的响应不同.肥料类型和径流发生时间是麦田径流氮素流失的主要影响因素.受监测年份降雨年型分配影响,RCU处理的季节径流氮素流失量(20.35 kg·hm^-2)较CN处理(10.49 kg·hm^-2)显著增加.生育后期是麦田氨挥发损失的主要时期,...     

Matching innovations with potential users, a case study of potato IPM practices

Through interviews and mail surveys, Ohio potato (Solanum tuberosum) growers were surveyed concerning their willingness to adopt three cultural controls being developed for management of the Colorado potato beetle, Leptinotarsa decemlineata (Say), which had become increasingly difficult to control. The principal objective of the research was to obtain a deeper understanding of how farmers make decisions to adopt or not adopt new techniques and how these decisions are related to farmers' educational backgrounds and the way they currently manage their farms. The three cultural management options emphasized ecological approaches to habitat management rather than ecologically disruptive chemical control: (1) using host plants in overwintering sites to slow the spring movement of the beetles to potato fields, (2) using larger potato plants at field borders than in the center of the field as a spring trap crop, and (3) concentrating beetles in relatively small undefoliated areas to be killed with heat in late summer. Most respondents would not adopt these alternative pest management strategies, mainly because they perceived an unsatisfactory trade-off between logistic difficulties and expenses and population suppression they would achieve compared with traditional chemical control measures. Education correlated positively and experience in farming negatively with the willingness to try new pest management techniques. Additionally, growers responding more negatively to questions regarding integrated pest management strategies were more willing to experiment with the alternative techniques, a result attributed to either the survey design or an indication of experience with the more intensive management effort required for integrated pest management. This profile of potential innovators should be used by researchers to establish partnerships with farmers that could assist with both the research and development of new farming techniques and the adoption of successful systems by other farmers.     

Impact of wildflower strips on biological control of cabbage lepidopterans

In a 2-year experiment we investigated whether wildflower strips can be used to enhance the control of cabbage moth, Mamestra brassicae L., and cabbage white butterfly, Pieris rapae L. At two sites, including six organically cultivated fields, M. brassicae egg parasitism and predation rates were determined along with an assessment of larval parasitism rates in M. brassicae and P. rapae using a DNA-based approach. Within each field, plots with and without wildflower strips were sampled and a grid design of 3 m × 3 m was used to analyze the spatial pattern of parasitism. The provision of wildflower strips provided an idiosyncratic effect on the control of lepidopterans: parasitism rates in M. brassicae eggs and larvae were not affected, whereas parasitism rates of larval P. rapae were significantly enhanced by the wildflower strips at one of the two sites. Moreover, at one site predation rates on M. brassicae eggs were significantly enhanced in the wildflower strip plots. Geostatistical analysis showed no distinct spatial patterns in parasitism rates. These results demonstrate that the provision of wildflower strips does not necessarily enhance biological control of lepidopteran cabbage pests and suggest that site-specific environmental factors strongly affect the impact of wildflower strips.     

Differential survival rates in a declining and an invasive farmland gastropod species

Individual marking by using transponders represents a promising tool to further investigate causes of population trends of farmland invertebrates and the dynamics of farmland biodiversity. Once common in agricultural fields the slug Arion rufus is now restricted to forests, whereas the closely related and similar Arion lusitanicus recently built up high populations. Here, it was tested whether (1) transponder tagging combined with artificial shelters for recapturing is a suitable approach for quantifying adult survival of farmland gastropods under real field conditions, (2) whether captive bred and wild A. lusitanicus differ in survival, and (3) whether in agricultural fields the declining slug A. rufus shows reduced survival rates compared to the invasive slug A. lusitanicus. One hundred and thirty transponder-tagged slugs were released and individual-based mark-recapture models were performed. Individual marking by using transponders proved to be a successful method for quantifying survival rates of the slugs. The favoured model showed no differences in survival or encounter rates between captive bred and wild A. lusitanicus. A. rufus showed significantly reduced survival rates compared to A. lusitanicus coinciding with their population trends in farmland areas. This might be due to differential susceptibility to habitat degradation, differential predation rates or promotion of the invasive competitor species. A further decrease of A. rufus in agricultural landscapes is expected.     

Influence of hedgerow and grassy field borders on ground beetle (Coleoptera: Carabidae) activity in fields of corn

Agricultural landscapes may be manipulated in ways that benefit predatory invertebrates by providing alternate food sources, overwintering sites, and refuge from farming activities. Ecological theory predicts that complex plant communities should support a richer community of natural enemies of pest insects than a simple plant community. A study was conducted in Iowa, USA to investigate the influence of the vegetative diversity of field boarders on the activity, species richness, and community similarities of predatory beetles occurring in corn fields.Ground beetle (Coleoptera: Carabidae) populations were compared among corn fields bounded by either complex hedges or simple grass edges. Directional pitfall traps were used to investigate activity patterns of beetles between border types and their adjacent corn fields. Beetles were trapped during four seasonal periods, based on the growth stage of corn. During corn emergence (May–June) when fields are barren, carabids were more active and species richness was higher in the corn fields bordered by woody hedges. The carabid species Scarites quadriceps, Scarites subterraneus, and Harpalus pensylvanicus, were more dominant in hedge sites as compared to grass sites at this time. Following corn–canopy closure, carabids were now more active in fields bordered by grassy edges, but beetle activity also remained high in the fields adjacent to woody hedges. Further analysis of the carabid communities by Bray–Curtis Similarity Index showed no difference among field edge types at any time of the season. Results indicate that both complex and simple field border habitats support abundant and diverse populations of carabids during most of the growing season. However, during the early growing season hedges appear to be more important than grass edges in supplying carabid beetles to corn fields. Woody hedges may serve as very important overwintering sites and as an early season refuge for predatory beetles in corn.     

Effects of bird predation on some pest insect populations in corn

Intensive agriculture has led to a decrease in biodiversity in many areas of the world. Poisoning birds directly or eliminating habitats suitable for birds within an agricultural landscape, may remove potential control agents of insect pests. The main objective of this project was to investigate the effects of excluding avian species from portions of cornfields through the use of bird-proof netting. Although pest levels were low and exclusion nets failed to affect corn yield, some differences were seen in insect pest population levels, supporting the view that insectivorous birds play a beneficial role in corn fields. Cutworms (Agrotis spp.) and weevils (Sphenophorus spp.) were found at higher density in plots where birds were excluded, especially those situated near the field edge. Data on aphids (Rhopalosiphum maidis) and European corn borer (Ostrinia nubilalis) were more variable but tended in the same direction. Only the adult Northern corn rootworm (Diabrotica longicornis) population was clearly not reduced by birds but infestation levels were extremely low.     

Integrated control of the root-knot nematode, Meloidogyne incognita, on black-pepper plantations in the amazonian region

In the Amazonian region, so-called foot-rot disease, caused by a fungus Nectria, occurs widely on black-peppers, Piper nigrum L., the roots of which are also heavily infested by the root-knot nematode, Meloidogyne incognita. Factorial experiments were conducted in this region during 1976–1978 to attempt to find out the effect of nematicide treatment, mulching with Imperata cylindrica, and non-host cover plantings, on the growth of black-peppers as well as on nematode population levels. Temic or Furadan treatment resulted in better plant growth and a reduced nematode population in the first year. Mulching resulted in exceedingly high plant growth, even though higher nematode populations were also observed. Under mulching conditions, soil temperatures at 5-cm depth seldom rose beyond 30°C throughout the year. Cover plantings of non-hosts, which had been selected by earlier inoculation tests, indicated remarkable retardation of plant growth of black-peppers, evidently due to the competition, and this also reduced the nematode population. Macroptilium atropurpureum (siratro) gave the smallest growth retardation of black-peppers. From these results, a combination of three procedures, i.e. Temic or Furadan treatment, mulching with grass straw, and cover-planting of non-hosts such as siratro, is recommended on black-pepper plantations for better plant growth and eventually better yield of black-peppers in the fields infested by root-knot nematodes.