Economic injury levels for Bemisia tabaci (Homoptera: Aleyrodidae) in cotton: impact of crop price, control costs, and efficacy of control

Field studies were conducted during 1993 and 1994 in the Imperial Valley, California and Maricopa, Arizona to examine relationships between densities of Bemisia tabaci (Gennadius) populations and cotton (Gossypium hirsutum L.) yields, and to estimate economic injury levels (EILs) for pest management application. Populations of B. tabaci were manipulated by applying different numbers of insecticide applications in replicated plots. Resulting insect populations and cotton lint yields were used to develop damage functions and to estimate EILs for all life stages in relation to variable cotton prices, insecticide costs, and pest control efficacy. Economic injury levels declined with increasing cotton prices and increased as the cost of control increased, however, these changes were relatively small, based on typical ranges in price and control costs. In contrast, the efficacy of control provided by insecticide applications had a large influence on EILs, with lower efficacies being associated with higher injury levels. We developed a multiple regression model that accounted for the dynamic changes in the EIL in relation to crop price, control costs, control efficacy, and potential yield. Based on average prices and reasonable control costs and efficacy, EILs ranged from 5.9–15.2 adults/leaf, 6.1–19.8 eggs cm⁻², and 1.7–4.7 nymphs cm⁻² of leaf area. Additional research is needed to more closely relate the costs of control to the suppression of insect populations, and to define economic thresholds that will enable pest managers to maintain pest populations below EILs.     

不同种植密度对棉花空间成铃分布的影响

为探究赣早5号在长江流域棉区适宜的种植密度,研究不同种植密度对赣早5号空间成铃分布以及产量的影响。试验设置6个种植密度处理(分别为15000株/hm²、37500株/hm²、60000株/hm²、82500株/hm²、105000株/hm²、127500株/hm²),定期测定棉花各器官干物质质量、籽棉产量等农艺性状。研究结果显示,随着种植密度的增大,棉花的株型结构由松散型逐渐变为紧凑型;单株干物质质量随种植密度的增加有减少的趋势,具有显著性差异;籽棉产量随着密度的增加呈现先升高再降低的趋势,其中种植密度在82500株/hm²产量最高,达到3707.01 kg/hm²,且其株型具有较大的成铃空间,单株成铃数也较高。综上所述,赣早5号的种植密度在82500株/hm²时拥有更好的株型结构,单株成铃率高,产量亦高。     

Plant density and self-thinning affect yield and quality of fibre hemp (Cannabis sativa L.)

To ascertain the reasons for the high plant mortality in fibre-hemp (Cannabis sativa L.) crops in the Netherlands changes in biomass yield, plant mortality and plant morphology were investigated in a hemp cultivar grown at initial densities of 10, 30, 90 and 270 plants m⁻². At 90 plants m⁻² this cultivar was compared with a high bast-fibre cultivar and a late-flowering cultivar. Rate of canopy establishment and early growth rate increased with increasing plant density. At 90 and 270 plants m⁻², plants died as a result of self-thinning. Self-thinning was associated with a reduced crop growth rate. In self-thinning stands, dry biomass (B, g m⁻²) was related to density of surviving plants (D, m⁻²) as log B = 3.81 − 0.304 log D. At the same crop growth rate, the rate at which plants died from self-thinning was higher in hemp than in other herbaceous dicots. The proportion of stem in the total dry matter increased with increasing plant density. Stem yield was maximum at 90 plants m⁻². Stem quality improved with increasing density as the bark content in the stem increased, but self-thinning reduced the bark content in the stem. Optimum plant density was close to that resulting after self-thinning. In hemp the relationship between yield and optimum plant density is approximated by the equation of its self-thinning line. The late-flowering cultivar yielded more than the other two cultivars because it grew faster during the latter part of the growing season.     

Use of UV reflective mulch to delay the colonization and reduce the severity of Bemisia argentifolii (Homoptera: Aleyrodidae) infestations in cucurbits

Effectiveness of UV reflective plastic mulch for the management of silverleaf whitefly (Bemisia argentifolii Bellows and Perring) was evaluated in selected cucurbits. The reflective mulch repelled silverleaf whitefly adults in pumpkin (Cucurbita maxima Duchesne), cucumber (Cucumis sativus L.) and zucchini squash (Cucurbita pepo L.). Reduced colonization by B. argentifolii adults resulted in reduced populations of nymphs and a delay and reduction in the incidence of silverleaf in pumpkin and zucchini squash. Reflective mulch was as effective in reducing nymphal B. argentifolii populations as was a pre-plant soil application of imidacloprid. Zucchini squash, pumpkin and cucumber yields were significantly higher in plants grown over reflective mulch than in those grown over unmulched soil. Zucchini squash yields from plants grown over reflective mulch also were higher than from plants grown in plots receiving a pre-plant application of imidacloprid. This study confirmed that UV reflective plastic mulch can be used to manage B. argentifolii and the mulches give protection equal to that provided by imidacloprid.     

Growth, gas exchange, water relations, and ion composition of Phaseolus species grown under saline conditions

We examined the effects of salinity on four wild (Phaseolus angustissimus, Phaseolus filiformis, P. microcarpus, and P. vulgaris) and two cultivated (P. acutifolius and P. vulgaris L.) Phaseolus species. Relative growth rate (RGR, g g⁻¹ per day), unit leaf rate (ULR, g m⁻² per day), leaf area ratio (LAR, m² g⁻¹), specific leaf area (SLA, m² g⁻¹), leaf weight ratio (LWR, g leaf g⁻¹), and rate of ion uptake were calculated for the period between 10 and 20 days after planting. Salinity significantly reduced RGR, ULR, LAR, and SLA whereas LWR showed no definite trend. In all species, except in P. filiformis, ULR, but not LAR, was significantly correlated with RGR, indicating that ULR was an important factor underlying the salinity-induced differences in RGR among species. In P. filiformis, high salinity reduced SLA, and consequently LAR. The significant correlation of SLA and LAR with RGR suggested that growth components affecting leaf area expansion were the primary factors explaining the inhibition of growth in this species. Increasing salinity progressively decreased leaf water vapor conductance. The rate of CO₂ assimilation decreased gradually with salinity, showing significant reductions only at the highest salt level (80 mM NaCl). Approximately two-thirds of the reduction in CO₂ assimilation rate at high salinity was attributable to reduced stomatal conductance. In P. filiformis, however, neither stomatal conductance nor CO₂ assimilation were affected by salt stress. Leaf water and osmotic potentials declined significantly as stress intensified. However, osmotic adjustment permitted the maintenance of positive turgor throughout the growth period. Salinity had a significant effect on tissue concentrations of Na⁺, K⁺, Ca²⁺, and Cl⁻ and on the uptake rate of Na⁺, K⁺, Ca²⁺, and Cl⁻. Thus, in addition to the toxic effects of high concentrations of Na⁺ and Cl⁻ in plant tissue, saline-induced changes in mineral nutrient uptake likely contributed to the reduction of plant growth. It appears that salt tolerance in P. filiformis is associated with Na⁺ exclusion and organ Na⁺ compartmentation in roots and stems as well as sustained K⁺ concentration in leaves and better stomatal control through osmotic adjustment. All other Phaseolus species are Na⁺ excluders, and maintained turgor-driven extension growth by accumulating Cl⁻ (osmotic adjustment), but subsequent weight gain reductions suggest that this led to ion toxicity.     

Seasonal abundance of the mirids, Lygus lucorum and Adelphocoris spp. (Hemiptera: Miridae) on Bt cotton in northern China

Lygus lucorum Meyer-Dür, Adelphocoris fasciaticollis Reuter and Adelphocoris lineolatus (Goeze) (Hemiptera: Miridae) are important secondary insect pests in cotton fields in northern China. The seasonal dynamics of their mixed populations on a transgenic variety expressing the insecticidal Bt protein Cry1A, and a cotton line expressing proteins of Cry1A and CpTI (cowpea trypsin inhibitor gene) were compared to seasonal dynamics on similar but non-transgenic varieties from 1998 to 2001. No significant differences were detected between population densities of these bugs on unsprayed normal cotton and unsprayed transgenic cotton. However, mirid damage on unsprayed transgenic cotton was significantly higher due to a reduced number of insecticide sprays against Helicoverpa armigera compared with the number of sprays in the normal cotton. This suggests that the mirids have become key insect pests in transgenic cotton fields, and that their damage to cotton could increase further with the expansion of the area planted to transgenic cotton if no additional control measures are adopted.     

Possible alternative utilization of Cynara spp.: I. Biomass, grain yield and chemical composition of grain

Globe artichoke (Cynara scolymus L.) and cultivated cardoon (C. cardunculus L. var. altilis DC.) are horticulturally important crop plants. These species have potential as biomass and oilseed crops. We field tested, for 3 years, two artichoke and two cardoon cultivars and one wild cardoon (C. cardunculus L. var. sylvestris Lam.) population on the Sicilian plain of Catania (37°27′ N, 15°04′ E, 10 m a.s.l.). On a 3-year average, the dry aboveground biomass resulted about 31 t ha⁻¹ in both cultivated cardoons, 18.8 t ha⁻¹ in wild cardoon, 13.7 t ha⁻¹ in globe artichoke ‘3/10 V.S.’ and 9.9 t ha⁻¹ in globe artichoke ‘374’ F₁. The caloric values of aboveground biomass (except for seeds), which was not significantly different among genotypes, ranged between 16 005 and 17 028 KJ kg⁻¹ of dry matter. The cultivated cardoon ‘Gigante di Lucca’ had the greatest grain yield (on 3-year average, 2.6 t ha⁻¹), whereas the two globe artichokes had the lowest yield (on 3-year average, 0.5 t ha⁻¹). Regardless of genotypes and years, the grains contain 20.1% crude protein, 24.4% oil, 18.5% crude fiber and 4.1% ash (dry weight basis). The grains of globe artichokes showed the highest crude protein content (21.6%), whereas those of cardoons the highest oil content (25.2%).     

Integrated Management of Whitefly, Bemisia tabaci (Gennadius) and Potato Apical Leaf Curl Virus in India

This paper reviews the importance of Potato apical leaf curl virus (PALCV) in India, the biology of its major vector Bemisia tabaci and possible control measures of PALCV and B. tabaci. PALCV has appeared as a new problem in potato growing areas of northwestern plains of India. The first report of PALCV was made from Hissar around 2000. PALCV is a whitefly (B. tabaci) transmitted viral disease and the symptoms are manifested primarily in the form of upward or downward curling of leaves, with 40–75% infection being recorded in cultivars grown in the Indo-Gangetic Plains of India. B. tabaci is a polyphagous pest that feeds on numerous fibre (particularly cotton), food, vegetable and ornamental plants. B. tabaci produces many generations in a year and reaches high population densities. To check the disease incidence, whitefly suppression using imidacloprid either as seed treatment or as foliar application early in the season is recommended. To minimize within-field spread of viruses, removal of virus-infected plants is suggested. Application of mineral and vegetable oils has been found to inhibit virus transmission and possibly can help to avoid difficulties with insecticide resistance in whiteflies.     

Sudanese cotton and the whitefly: a case study of the emergence of a new primary pest

In the late 1970s the whitefly Bemisia tabaci (Gennadius) became the primary cotton pest in the Sudan, superseding the American bollworm Heliothis armigera (Hübner). DDT and a DDT/dimethoate combination were used to control the bollworm and, simultaneously, jassids and whiteflies. B. tabaci, a secondary pest at first, became resistant to dimethoate by frequent selections from 1964 onwards. At the same time, fertility stimulation occurred due to DDT residues on cotton plants. Finally, resistance reached a level so that the whitefly were not controlled by dimethoate, monocrotophos or other organophosphorus insecticides, and stimulation by DDT could exert its full effect. The consequence of this was a tremendous flare-up of the whitefly by 1980/81. This train of events was concluded from laboratory and field studies of the resistance patterns, as well as the acceleration effects from DDT residues on plants to the whitefly. A current hypothesis claiming that the problems arose from the elimination of beneficial insects through insecticide applications is reviewed in the light of experimental evidence and practical experience.     

不同氮肥水平下优质高产软米粳稻的产量与品质差异

【目的】明确优质高产软米粳稻的产量和品质对氮肥的响应特征。【方法】在前期品种筛选的基础上，选择2个优质食味高产型软米品种为研究对象，设置60 kg/hm²(N1)、120 kg/hm²(N2)、180 kg/hm²(N3)、240 kg/hm²(N4)、300 kg/hm²(N5)与360 kg/hm²(N6) 6个氮肥(以纯氮计)水平，对其产量性状和品质指标进行了测定与分析。【结果】依赖于单位面积穗数、每穗粒数和群体颖花量的协同增加，软米产量在N5下最高，但与N4间无显著差异。随施氮量增加，米粒的外观、黏度、平衡度和食味值呈先增后减，而硬度则先减后增，并在N4或N5下出现峰值;出糙率、出精率和整精米率均随施氮量增加而提高，但垩白米率和垩白度呈先降后增，并在N5水平下最低。随施氮量的增加，直链淀粉含量和胶稠度下降，蛋白质含量升高。米粉峰值黏度、热浆黏度、崩解值和最终黏度随施氮量的增加呈先增后减，在N4或N5下最高。【结论】因此，优质食味软米在240 kg/hm²和300 kg/hm²条件下取得产量和品质的协调，240 kg/hm²是品质、产量和效益兼顾的最佳施氮量。     

水稻矮缩病毒对介体昆虫黑尾叶蝉生物学参数及种群增长的影响

【目的】 水稻矮缩病毒(RDV)是水稻普通矮缩病的病原。该病害主要依赖于黑尾叶蝉经卵以持久增殖方式传播,危害水稻。本研究旨在明确RDV对黑尾叶蝉存活、发育、繁殖和种群增长的影响,分析病毒对介体昆虫的间接影响。【方法】 采用室内实验比较了黑尾叶蝉在健康水稻及感病水稻上的发育繁殖情况,组建了实验种群生命表,并调查了RDV对种群增长的影响。【结果】 与健康水稻相比,感病水稻上叶蝉若虫期存活率更高,雌若虫发育历期显著缩短,雄成虫寿命显著延长,产卵量显著增加,其他生物学参数无显著差异。五个生命表参数仅净生殖率(R₀)存在显著差异,感病水稻上叶蝉R₀显著高于健康水稻。饲喂感病水稻的养虫笼内叶蝉种群增长更快,总成虫数量更多,在接虫后的第4、5和6月显著高于健康水稻上的数量。【结论】 水稻矮缩病毒可以提高黑尾叶蝉的存活率和产卵量,并促进种群的增长。     

Sampling and management of Bemisia tabaci (Genn.) biotype B in Australian cotton

Data on seasonal population abundance of Bemisia tabaci biotype B (silverleaf whitefly (SLW)) in Australian cotton fields collected over four consecutive growing seasons (2002/2003–2005/2006) were used to develop and validate a multiple-threshold-based management and sampling plan. Non-linear growth trajectories estimated from the field sampling data were used as benchmarks to classify adult SLW field populations into six density-based management zones with associated control recommendations in the context of peak flowering and open boll crop growth stages. Control options based on application of insect growth regulators (IGRs) are recommended for high-density populations (>2 adults/leaf) whereas conventional (non-IGR) products are recommended for the control of low to moderate population densities. A computerised re-sampling program was used to develop and test a binomial sampling plan. Binomial models with thresholds of T=1, 2 and 3 adults/leaf were tested using the field abundance data. A binomial plan based on a tally threshold of T=2 adults/leaf and a minimum sample of 20 leaves at nodes 3, 4 or 5 below the terminal is recommended as the most parsimonious and practical sampling protocol for Australian cotton fields. A decision support guide with management zone boundaries expressed as binomial counts and control options appropriate for various SLW density situations is presented. Appropriate use of chemical insecticides and tactics for successful field control of whiteflies are discussed.     

拟南芥生物钟双突变体lhycca1营养生长时相转变

高等植物生长发育阶段可分为营养生长和生殖生长2个阶段,其中营养生长阶段中只有通过营养生长时相转变方可进入生殖生长阶段。营养生长时相转变(vegetative phase change,VPC)是植物从幼龄期(juvenile stage)到成熟期(adult phase)的转变,受到基因表达的调控。生物钟(circadian clock)相关基因LHY和CCA1单独作用延迟VPC的发生,这2个基因的共同作用下VPC是否受到影响尚未见报道。本研究以拟南芥(Arabidopsisthaliana)为研究对象,通过形态和茎尖分生组织(shoot apical meristem,SAM)解剖结构观察及调控因子miR156和靶基因SPL3的表达变化,分析LHY和CCA12个基因在VPC过程中的作用。结果表明:双突变体lhycca1生长周期为15d,莲座叶第5片时(第10天)出现远轴面表皮毛,此时叶基角和叶长宽比增大且茎尖分生组织凸起明显,miR156和SPL3的表达水平在植物生长发育阶段呈负相关变化。而野生型生长周期为20 d,莲座叶第6片(第15天)时才出现远轴面表皮毛、叶长宽、叶基角、SAM、miR156和SPL3的变化。这些结果说明在LHY和CCA1的共同作用下,VPC提前发生,LHY和CCA1 2个基因参与VPC的调控。     

氮肥用量和栽插密度对杂交粳稻辽优5206生长与产量性状的影响

采用裂区设计,研究了氮肥用量和插植密度对杂交粳稻辽优5206生长和产量性状的影响,为北方粳稻高产高效栽培提供依据。结果表明,随着施氮量增加,水稻分蘖数、抽穗期干物质量、拔节期SPAD值、株高和穗长显著增加,有效穗数、穗粒数和产量虽增加但不显著;随着栽插密度的增加,水稻分蘖数、干物质量、有效穗数明显增加,灌浆期SPAD值、株高、穗长、穗粒数显著降低,抽穗期SPAD值、结实率和产量则先增后降;氮肥用量和密度在产量等多数性状上互作效应不显著;取得高产的最佳肥密组合是240 kg/hm²和16.7万丛/hm²。     

Fungicidal control of metalaxyl-insensitive strains of Bremia lactucae on lettuce

Strains of B. lactucae insensitive to 0.01 g a.i. l⁻¹ metalaxyl have been detected in all the lettuce-growing districts of South Australia. Despite this, applications of a formulated mixture of 0.25 g a.i. l⁻¹ metalaxyl and 2 g a.i. l⁻¹ mancozeb every 7–10 days controlled downy mildew in field experiments, where similar applications of either metalaxyl or mancozeb alone were ineffective. Protectant schedules of either 0.3 g a.i. l⁻¹ dimethomorph or 2–2.4 g a.i. l⁻¹ phosphonic acid also controlled downy mildew, but were less effective than the metalaxyl/mancozeb formulation. Mixtures of either dimethomorph or phosphonic acid with mancozeb enabled the time between the sprays to be increased to 14 days without significantly reducing control. Fungicide applications increased marketable yield by 60% compared with that of the unsprayed plants. Drenching seedlings with 4 g a.i. l⁻¹ phosphonic acid controlled downy mildew for at least 14 days and should prevent the spread of the disease from plant production areas.     

Glasshouse and field evaluation of fungicides for the control of Septoria apiicola on celery

Propiconazole was more effective than either triadimenol or hexaconazole when applied after infection, for the control of Septoria apiicola on celery seedlings. In three out of four glasshouse experiments, 25 mg propiconazole I⁻¹ controlled S. apiicola completely when applied within 3 days after inoculation. Propiconazole and triadimenol at 5–15 mg l⁻¹ were also effective when applied 2 days after inoculation. Soil applications of a granular formulation of triadimenol (up to 20 mg per plant) controlled S. apiicola for 5 weeks on celery seedlings grown in pots and, in the field, granules at 100 mg per plant applied at planting were effective for 6 weeks. In two other field experiments the most effective treatments were foliar sprays of 25 mg propiconazole l⁻¹ applied every 7–10 days with or without the addition of anilazine or chlorothalonil.     

New genes for resistance to green leafhopper, Nephotettix virescens (distant) in rice, Oryza sativa L.

The inheritance of resistance to the green leafhopper, Nephotettix virescens (Distant) (Homoptera: Cicadellidae), in 12 cultivars of rice (Oryza sativa L.) was studied at Joydebpur, Bangladesh. The resistance of Kosatawee is governed by a single recessive gene. The remaining 11 varieties possess single dominant genes for resistance, which are different from the genes Glh 1, Glh 2, Glh 3 and Glh 5. The single dominant genes conveying resistance in TAPL 796, Ptb 18 and IR36 are allelic to each other but are non-allelic to the dominant resistance gene of Maddai Karuppan. The resistance genes in TAPL 796 and Maddai Karuppan were designated Glh 6 and Glh 7 respectively. The dominant resistance gene in Sulai is independent of Glh 6, but its allelic relationship to Glh 7 is not known. The allelic relationships of the dominant genes for resistance of Sulai, TAPL 628, TAPL 651, Leu-Wei-Theu, Bir-co-se-mao-17, Gu-win-gu-gi-goo, and Dikwee to Glh 6 and Glh 7 need to be investigated.     

OsAMT1.1 Expression by Nitrate-Inducible Promoter of OsNAR2.1 Increases Nitrogen Use Efficiency and Rice Yield

Nitrate(NO₃^-) and ammonium(NH₄⁺) are two main inorganic nitrogen(N) sources during crop growth.Here,we enhanced the expression of OsAMT1.1,which encodes a NH₄⁺ transporter,using the NO₃^--inducible promoter of OsNAR2.1 and an ubiquitin promoter in transgenic rice plants.Under field condition of 120 kg/hm² N,agronomic N use efficiency,N recovery efficiency and N transport efficiency,and grain yield o...     

Overwintering and population dynamics of Bemisia tabaci biotype B in greenhouse during the spring in northern China

Since the sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B invaded southern China in the mid-1990s, it had spread to most other regions of the country, and become an important pest in agricultural and horticultural production. Investigations on overwintering of B. tabaci biotype B and its spring reproduction in northern China were conducted to determine the main factors that might contribute to an understanding of the population dynamics of this pest for developing improved pest control strategies. A cold hardiness test showed that when exposed for 10 h at −10 °C, mortalities of eggs, nymphs, and adults reached to 86.6%, 88.4%, and 100%, respectively, suggesting that it is probably impossible for feral populations of B. tabaci to survive in the winter under natural environmental conditions in northern China. A survey on vegetables, ornamental plants and weeds in greenhouses at Hebei Province and Beijing in northern China revealed at least 14 species of plants on which B. tabaci fed during the winter and spring. Lycopersicon esculentum Mill, Brassica alboglabra Bailey, Ficus carica L., Euphorbia pulcerrima Wild, and Hemelia patens Haence were the main host plants. Further research on the population dynamics of B. tabaci on three major greenhouse hosts; tomato, cucumber, and melon, indicated that densities remained at a low level during the winter, but increased steadily from February to March until migration into field crops in April. It is concluded that the control of the insect in greenhouse in winter and spring can play an important role for seasonal management of this pest in northern China.     

Control of maize pests with imidacloprid seed dressing treatment in Catalonia (NE Iberian Peninsula) under traditional crop conditions

The effects of treating maize seed with imidacloprid to prevent damage by soil pests, aphids, leafhoppers and the first generation of corn borers was evaluated in the field by comparing treated with untreated commercial plots in a 5-year study in Catalonia (NE Iberian Peninsula). The treatment reduced the incidence of cutworms (Agrotis segetum), wireworms (Agriotes lineatus), the first generation of the corn borer Sesamia nonagrioides and leafhoppers (Zyginidia scutellaris). However, treated plots were attacked significantly more by Ostrinia nubilalis. The treatment was effective in reducing aphid densities from maize emergence to mid June. What happened later depended on the relative abundance of aphid species. Rhopalosiphum padi seems to be more sensitive than Metopolophium dirhodum whose population can be enhanced after flowering in plots treated with imidacloprid. The treatment did not avoid aphid alate colonisation and MDMV infection was not prevented. The greater damage on untreated plants caused by wireworms, cutworms and the first generation of S. nonagrioides, and the densities achieved by aphids, was insufficient to produce yield differences between treatments, and only leafhopper damage led to economic damage. Imidacloprid favours the attack of the European corn borer, thus masking the potential increase in yield.