Patchy distribution of weeds and some implications for modelling population dynamics: a short literature review

Until recently the modelling of crop-weed interactions has largely ignored the complexities resulting from the patchy distribution of weeds and the multi-species nature of weed communities. Some progress has now been made in dealing with these two sources of variation. A population dynamical approach has proven to be quite helpful in this respect. In this approach the whole life-cycle of the species is considered, divided in a step by step fashion into separate stages, thereby offering a top-down modelling approach. Such models can easily be extended over a period of years, helping in developing long-term control strategies: complexity can be added as the need arises. Spatial heterogeneity can be taken into account by explicitly defining a spatial scale and the dispersal process. The multi-species nature of competition can be dealt with by using neighbourhood models of plant interference. A few recent contributions from the literature, using weeds as an example, are reviewed here against a more general background of weed demography.     

苜蓿蓟马的发生规律和药剂防治试验

在陕西关中地区研究了苜蓿蓟马优势种群、种群数量、危害特征、田间消长规律等。结果显示:牛角花齿蓟马(Odontothripsloti)是优势种;蓟马主要危害第二、三茬苜蓿,7～8月份是苜蓿蓟马若虫的发生危害高峰期。选用高效氯氰菊酯、吡虫啉、艾美乐和围打蓟虱蚜4种药剂防效比较表明,高效氯氰菊酯的防治效果最好,持效期长,成本低。     

Effect of botanicals on the population dynamics ofNephotettix virescens, rice tungro disease incidence and yield of rice

Leaf extracts ofVitex negundo L,Synadenium grantii Hook. f. andProsopis juliflora (SW) DC, and cake ofAzadirachta indica A. Juss. were evaluated for their efficacy in reducing the population of the green leafhopper,Nephotettix virescens (Distant), and its transmission of rice tungro virus under field conditions. All four plant species tested reduced the population of the vector significantly in both the nursery and main field. The lowest population of the vector was recorded with application of neem cake at 5 kg/0.032 ha of nursery, followed by foliar spray of neem seed kernel extract at 5% in the main field. Rice tungro disease incidence was also less in this treatment, with maximum grain yield of 3580 kg/ha in ‘Kharif’ (July-Oct.) and 3257 kg/ha in ‘Rabi’ (Nov.-March) seasons, and a cost:benefit ratio of 1:3.9 in both seasons. However, the maximum cost:benefit ratio of 1:5.6 and 1:5.8 in Kharif and Rabi seasons, respectively, was recorded withV. negundo.     

菱角小萤叶甲种群动态研究

对菱角小萤叶甲在菱塘的发生数量调查和分析表明,菱角小萤叶甲种群数量在一年中春末夏初和夏末秋初各有一个高峰期。温度是影响菱角小萤叶甲种群数量消长的关键因子;聚集度指标的分析表明,菱角小萤叶甲在菱塘呈聚集分布。聚块性指标与平均密度独立,适合用于分析菱角小萤叶甲分布型的时序变化;在控制条件下菱角小萤叶甲种群动态的研究表明,该虫具有较强的种群数量调控能力。     

云南石榴蓟马种类组成及其种群动态

2007-2008年对云南甜石榴和酸石榴两种石榴上蓟马种类及其种群动态进行了系统调查、标本采集、种类鉴定。结果表明,为害石榴的蓟马有10种,分别为西花蓟马(Frankliniella occidentalis)、丽花蓟马(F.intonsa)、黄蓟马(Thripsflavus)、黄胸蓟马(T.hawaiiensis)、棕榈蓟马(T.palmi)、烟蓟马(T.tabaci)、茶黄硬蓟马(Scirto-thrips dorsalis)、端大蓟马(Megalurothrips distalis)、华简管蓟马(Haplothrips chinensis)和Thripssp.,其中西花蓟马是云南石榴蓟马的优势种。不同石榴品种上蓟马种类不同,甜石榴上有西花蓟马、丽花蓟马、黄蓟马、棕榈蓟马、烟蓟马、黄胸蓟马、端大蓟马、茶黄硬蓟马和蓟马属1种,酸石榴上蓟马种类有西花蓟马、丽花蓟马、黄蓟马、棕榈蓟马、烟蓟马、端大蓟马、茶黄硬蓟马、华简管蓟马和蓟马属1种,黄胸蓟马仅在甜石榴上发生为害。在石榴不同生育时期,发生为害不同,其中成虫和若虫集中为害花,造成麻点特征。     

麦长管蚜自然种群结构动态的初步研究

采用田间系统调查的方法,观察了麦长管蚜在小麦拔节期一成熟期种群结构的动态.结果显示,麦长管蚜在种群发展过程中世代重叠,内部组成结构是一个有翅型与无翅型、成虫与若虫并存的混合体;各组分占种群的比例不均等.并随着小麦生育期和麦蚜种群发展过程而变化.在小麦乳熟期,翅型和虫态结构的比例表现为有翅型高于无翅型.若虫低于成虫.在其他生育期,则有翅型低于无翅型,低龄若虫>成虫>高龄若虫.结果表明,麦长管蚜内部结构的比例动态与小麦生育期关系密切,其组成结构特征直接反映了麦长管蚜种群的兴衰.     

Predictive models of weed population dynamics

Many of the challenges faced by weed ecologists can be met only by the capability to predict the responses of weed populations to changes in their environment or management. In spite of this, a review of papers published in Weed Research suggests that weed ecologists are remarkably reluctant to produce detailed, quantitative predictions. This may result from uncertainty in the accuracy of predictions and indeed, a variety of reasons have been put forward to suggest that the potential utility of weed models may be limited in this regard. In this study, we review the applications to which weed models have been put. Focusing on predictive population modelling, we highlight several limitations that can lead to failures of this approach and we discuss the likely prospects for weed population modelling. We make three points regarding the future of weed modelling. First, owing to prohibitive data requirements, the development of highly mechanistic models that attempt to make detailed predictions of weed population numbers is unlikely to be very successful. Second, data collection for developing weed models needs to be rethought. Weed models are most commonly compromised by a lack of spatial and temporal replication, preventing modellers from measuring parameter variability and error effectively and limiting assessments of model uncertainty. Finally, the utility of models needs to be better appreciated; models are key tools in making long range predictions of how management will affect weed populations, but, we estimate, they are used in only a small fraction of studies. Without the further development of models for weed population dynamics, our ability to predict long-term dynamics will be restricted.     

油菜小麦邻作模式对麦蚜主要天敌种群动态以及小麦生产的影响*

麦蚜是危害我国小麦生产的重要害虫。本试验探索了油菜小麦邻作模式以及小麦单作模式对麦蚜主要天敌发生的影响,以小麦和油菜交界处向两边各在0、2、4、6、8、16 m处设立试验小区,记录麦蚜主要天敌发生数量以及测定小麦株高、穗长、穗重、千粒重,揭示油菜小麦邻作模式对小麦生产的影响。结果表明：随着油菜的成熟,瓢虫逐渐向油菜小麦邻近处转移,且迁移的最有效距离为4 m;对邻作小麦田蚜茧蜂数量最高峰当日数据进行分析,发现除最高的0 m（2009年）和4 m（2010年）处外,其他各距离之间不存在显著差异,而单作田各距离之间蚜茧蜂数量上的差异不明显;相比于小麦单作模式,油菜小麦邻作显著提高了小麦的株高、穗长、穗重、千粒重。总之,油菜小麦邻作模式有利于麦蚜主要天敌向小麦田转移,并能提高小麦的产量和生物量。     

Separation of long and short particles of tobacco rattle virus with polyethylene glycol

Two methods to separate long and short particles of tobacco rattle virus with polyethylene glycol 6,000 (PEG) are described. The first is based on specific precipitation, the second on specific solubilization of particles with different lengths at different PEG concentrations. The results of the separations are comparable to, or better than those obtained by sucrose-gradient centrifuging. The advantage of the methods using PEG is that no expensive equipment is required.Samenvatting Twee methoden om lange en korte deeltjes van het tabaksratelvirus met behulp van polyethyleenglycol 6000 (PEG) te scheiden worden beschreven. De ene is gebaseerd op specifieke precipitatie, de andere op specifieke oplosbaarheid van deeltjes met verschillende lengten bij verschillende PEG-concentraties. De resultaten van de scheidingen zijn even goed als of beter dan die van scheidingen verkregen door centrifugeringen op een suikergradiënt. Het voordeel van de PEG-methoden is gelegen in het feit dat er geen kostbare apparatuur voor nodig is.     

培肥措施对植物线虫种群数量动态的影响

以华北高产粮区山东桓台县冬小麦-夏玉米轮作田为试验基地,研究培肥措施对植物线虫种群数量动态变化的影响。结果表明各施化肥(尿素)处理组线虫种群数量高于不施肥对照组。整个生长季,化肥使植物线虫种群数量增加;化肥+秸秆加剧植物线虫数量增加;化肥+秸秆+有机肥(猪粪)使植物线虫数量减少。化肥和秸秆还田增加植物线虫发生量,有机肥降低植物线虫增长数量,应提倡多施用有机肥。     

烟草码绢金龟成虫种群数量发生消长规律初探

码绢金龟(Maladerasp.)属鞘翅目金龟子科,是西南烟区为害烟草的主要害虫之一。该虫主要以成虫在大田为害烟草。在金龟子发生数量大的时期,码绢金龟占有相当大的比例,最高时可达80%以上。从烟草团棵到现蕾期,是烟草生长的旺季,此时也是成虫为害的盛期。成虫将叶片咬食成孔洞、缺     

庐江县稻飞虱群落演变特点、大发生原因及防治对策

通过分析历史资料、调查研究及田间试验,归纳了安徽省庐江县稻飞虱群落演变规律,分析了2006年褐飞虱发生特点、大发生成因,并提出相应的防治对策。1964年以来稻飞虱群落演变规律可分为4个阶段,其间相对于白背飞虱,褐飞虱种群数量分别为高、低、平、高水平,总态势近于“U”字形。当前褐飞虱发生特点主要有迁入虫源早、迁入量大,种群增量大,危害时间长,危害世代多,危害面积广。回升和暴发可能的原因包括水稻品种、作物布局和栽培措施改变,秋季气温升高,褐飞虱对吡虫啉产生抗药性,害虫天敌下降,以及农民防治组织缺乏。防治对策强调改进虫情测报、适时早治、适当多治、选用正确药剂、改进施药方法,并建立健全基层防治组织。     

稻-鸭生态系统中二化螟消长动态研究

2003年4～10月,在稻鸭共栖田中,对二化螟发生规律的系统研究结果表明,稻田养鸭能显著减轻二化螟的为害。与对照相比,中稻田养鸭区二化螟为害株率减少13.4%～47.1%;晚稻田减少62.2%。稻鸭共栖能减少化学农药的使用量,具有较好的经济、社会和生态效益。     

棉大卷叶螟的年生活史与种群动态

经过3年田间调查及室内饲养观察,绘制了江淮棉区棉大卷叶螟年生活史图。调查结果显示,该棉区棉大卷叶螟年发生5~6代,主要以第5代老熟幼虫越冬,越冬幼虫于次年4月中下旬化蛹,棉田幼虫始见于6月中下旬,但发生量少,进入7月中下旬后虫量开始上升,8~9月上旬达到高峰。近3年的调查数据表明,该棉区棉大卷叶螟种群数量发生大,其中常规棉田3年百株平均虫量达1 656~2 324头,并对棉花造成了较大损失。转基因棉田棉大卷叶螟种群数量受到明显抑制,3年百株虫量为619~1 358头。     

上海盆景植物寄生线虫种类与群体动态

调查上海地区出口盆景，发现15属植物寄生线虫，其中垫刃线虫、螺旋线虫、环线虫、根结线虫、毛刺线虫、短体线虫、剑线虫、矮化线虫、滑刃线虫等是上海口岸盆景植物主要寄生线虫种类。盆景根围线虫群体密度在1年中的变化与气候变化明显相关。从春到秋，种群数量呈增长趋势，群体结构呈多样化发展，秋天是线虫种群数量、种类最为繁盛时期。     

The implication of stubble tillage for weed population dynamics in organic farming

In practical farming, early and shallow stubble tillage is carried out post‐harvest to stimulate germination of freshly ripened crop and weed seeds, to kill the resulting seedlings and hence to reduce the input into the soil seedbank. Additionally, it aims at reducing perennial weeds by mechanical damage. In this paper, field experiments and laboratory studies are presented which show that stubble tillage can reduce perennial weeds. However, it had a variable effect on annual weeds. After 5 years of experimentation, no effect of stubble tillage was seen on the aboveground vegetation. In contrast, the soil seedbank of the control was roughly doubled where the stubble had been left uncultivated until autumn ploughing. These results indicate that practical experience which assumes that stubble tillage reduces annual weed populations may be correct, despite the fact that in other published studies stubble tillage exerted no control on annual weeds or had a variable effect. This will have practical application in organic arable production systems.     

山东省烟草孢囊线虫的群体动态和世代发生特点

为探究烟草孢囊线虫Heterodera glycines的田间侵染循环特点,2012年从山东省诸城市某烟田定点定期取样,对土壤和根组织中的线虫进行分离和染色后镜检并计数。结果显示,4月29日至9月9日在土壤中均检出烟草孢囊线虫2龄幼虫（J2）,有4个发生高峰,最大密度在7月9日,为7.3条/100 g土壤。5月13日至8月13日在根组织中出现J2,有3个明显高峰,最大密度在7月15日,为30条/10 g根;年轻雌虫在5月21日至8月30日形成,有3个明显高峰,最大密度在7月2日,为54条/10 g根。研究表明,烟草孢囊线虫 1年发生4代,平均世代历期27 d;后两代存在明显世代重叠现象;第4代线虫侵染量很少,且根内线虫发育不良。     

黄土高原苹果金纹细蛾种群动态

为明确金纹细蛾种群动态规律,采取时空不放回抽样的调查方法,应用分布型测定、生态位指标及聚类法分析不同套种苹果园种群变化.结果显示,黄土高原苹果园金纹细蛾虫疤显现于6月;7月种群分布先均匀后聚集;8月相对多度强势上升,危害状明显;9～10月数量增长显著.树冠分布为:垂直方向下＞中＞上且差异显著,水平方向差异不显著.总体为聚集分布,个体间相互吸引.生态位占居:垂直、水平和时序三个方向上分别为0.179、0.371和0.594,对树冠下部资源利用达53.73％,上部几乎没有.对树冠四方位资源利用以北、东最高,分别达27.90％和21.66％;与山楂叶螨的生态位重叠指数垂直方向为92.65,水平方向为64.95,时序上为66.36.进入8月后苹果幼龄园不同套种水平下的优势度指数明显增加,中旬增幅最大,其中套种黄豆园最高,套红薯园最低,杂草丛生园则波动较大.     

有机稻田白背飞虱种群动态及其天敌作用

为组建有机稻田白背飞虱种群生态控制系统,系统调查了实施有机耕作一年后白背飞虱种群动态,并应用生命表技术评价了自然天敌的作用.结果表明,在有机早稻田中白背飞虱发生2个世代,高峰期分别为5月上中旬和6月上中旬,平均百丛虫量分别为435.4和216.4头,干扰作用控制指数IIPC分别为0.3079和0.4044.水稻移栽后天敌回升迅速,移栽15天迁入稻田的蜘蛛为同期常规稻田蜘蛛的2.56倍;捕食性天敌、寄生性天敌数量在移栽42、38天分别为同期常规稻田的1.64与1.40倍.将天敌因子的作用相加,"捕食及其它"和"寄生"因子对白背飞虱种群的控制作用强,其排除作用控制指数(EIPC)值显著高于常规稻田相应作用因子.