三种杀虫剂对麦田蚜虫和天敌的影响

通过对施用杀虫剂吡虫啉、抗蚜威、广谱性杀虫剂氧化乐果对麦田蚜虫和天敌的影响进行分析 ,结果表明 ,施用杀虫剂对麦田蚜虫防效高 ,对其天敌有保护作用 ,且瓢蚜比降低。使用 1 0 %吡虫啉( 1 0g 667m2 )后 5～ 2 5天瓢蚜比为 1∶34～ 1∶1 70 ;用 50 %抗蚜威 ( 5g 667m2 )后 1 0～ 2 0天瓢蚜比为 1∶31～1∶1 95;而广谱性杀虫剂氧化乐果 ( 50mL 667m2 )对麦田蚜虫防效好 ,对天敌杀伤力大 ,药后 1 5天瓢蚜比为1∶2 65。施用化学农药可使蚜茧蜂寄生率提高。     

Effects of inter-annual landscape change on interactions between cereal aphids and their natural enemies

The agricultural intensification and the subsequent habitat changes in agroecosystem can strongly affect biological control services. We here examine the influence of inter-annual landscape change in wheat field area on interactions of cereal aphids and their natural enemies, as well as the efficacy of biological control using data collected from a 4-year experiment in Northwest China. Two hypotheses were tested. (i) Population densities decline following an inter-annual expansion of wheat crop proportion cover due to dilution and crowding effects. (ii) Species that are specialists or at higher trophic levels are more sensitive to bottom-up disturbance by inter-annual change in percent cover of wheat crop. Results showed the population densities of one cereal aphid (Macrosiphum avenae), one parasitic wasp (Aphidius avenae), two specialist predators (ladybirds: Hippodamia variegata and H. tredecimpunctata) and one hyperparasitic wasp (Pachyneuron aphidis) declined following the expansion of wheat crop areas, supporting the predictions of inter-annual dilution and crowding effects. In contrast, the populations of one cereal aphid (Schizaphis graminum), one parasitic wasp (A. gifuensis), two generalist predators (spiders: Pardosa astrigera; carabid beetles: Chlaenius pallipes), and two hyperparasitic wasps (Asaphes suspensus, and Alloxysta sp.) did not respond to inter-annual landscape change. The two hypotheses were partially supported but with noticeable exceptions, and the bio-control efficiency declined with the increase of the proportion cover of wheat field in agricultural landscape. Overall, different responses of cereal aphids and their natural enemies make it difficult but still possible to optimize inter-annual landscape change for enhancing the parasitism rate and predator-prey ratio.     

Effects of pirimicarb, dimethoate and benomyl on natural enemies of cereal aphids in winter wheat

The insecticides, pirimicarb and dimethoate are commonly applied to cereal crops in the UK and when this study was begun the fungicide benomyl was also regularly used. The effects of these chemicals on natural enemies of cereal aphids were examined in replicated plots of winter wheat. Benomyl did not affect any of the groups examined but it was applied early in the season (April/May) when most natural enemies were few or absent from the crop. Numbers of carabid beetles, staphylinid beetles and spiders, sampled using pitfall traps and a vacuum net sampler, were all reduced by dimethoate but not by pirimicarb, although these effects were only detected by pitfall traps when the small plots were surrounded by polyethylene barriers to prevent inter-plot movements. Parasitic Hymenoptera were decreased by both insecticides, partly due to direct toxicity and partly to host removal. Data on the aphid predators, Coccinellidae, Syrphidae and Chrysopidae were inconclusive because there were very few in the crop due to the scarcity of aphids. Ways in which pesticides can affect natural enemy populations other than by direct mortality and the dangers associated with routine, prophylactic pesticide applications are discussed.     

小麦蚜虫的优势天敌及对蚜虫的自然控制

小麦蚜虫天敌资源丰富 ,其优势天敌在甘肃环县有 30余种。各种蚜虫天敌在小麦不同生育期先后衔接、互相配合 ,对小麦蚜虫的发生起着有效的自然控制作用 ;蚜虫与天敌在不同年际间也呈现出一定的规律性变化。保护利用天敌应与测报、防治和改善生态环境相结合     

小麦和牧草上的蚜虫与天敌种群动态及其相互关系

2008年4月底至6月初在山东禹城调查了小麦和3种牧草上的蚜虫和天敌种群密度。结果表明,麦蚜种群高峰期在5月中旬,寄生蜂和瓢虫的高峰期比蚜虫分别滞后5—10d和15～20d;麦蚜种群增长率与天敌种群密度变化呈负相关,其中与瓢虫的相关性达到显著水平;4月底至5月初小麦抽穗期是麦蚜种群爆发的关键时期,天敌密度低、害益比大是爆发的重要原因;4月底至5月初,牧草上的天敌密度是小麦上的2～3倍。牧草在麦蚜种群生态调控中具有潜在应用价值。     

黄色粘板对小麦蚜虫及其天敌的诱集作用

为明确黄色粘板对小麦蚜虫及其天敌的诱集作用,2010和2011年,在中国科学院河北栾城县农业生态系统试验站,通过在小麦田间悬挂黄板,对其诱杀小麦蚜虫效果及对小麦蚜虫天敌的影响进行了调查统计分析。结果表明,当地悬挂的黄板可以诱杀7目30余种昆虫,优势种是蝇类,而非小麦蚜虫。悬挂区内不进行化学防治时,黄板诱杀蚜虫数量与其相应百株虫量之间呈显著的线性相关,进行化学防治时,两者之间的线性相关不显著。黄板可以诱杀多种小麦蚜虫的天敌,灌浆期前后,黄板诱集到的益害比都大于1,最高可达45.50。在综合考虑黄板对小麦蚜虫及其天敌的诱杀作用,以及可能影响黄板诱集效果的气象条件后,初步结论是在河北栾城及周边地区,黄板可用于早期迁入小麦有翅蚜的监测,但不适合防治小麦穗期的蚜虫。     

自然天敌对苗蚜和伏蚜控制作用的定量分析

【目的】为了合理利用自然天敌,定量评价棉田自然天敌对苗蚜和伏蚜的控制作用。【方法】采用接虫罩笼法结合系统调查。【结果】发现苗蚜的主要自然天敌是龟纹瓢虫Propylaea japonica Thunberg和异色瓢虫Harmonia axyridis Pallas,大部分时间能够有效的控制苗蚜种群在防治指标以下,控害指数高达91%;伏蚜主要自然天敌是蜘蛛、草蛉和龟纹瓢虫,由于其种群数量太少,益害比低,对伏蚜控害指数始终低于20%,无法有效的控制伏蚜种群。【结论】结果提示,应根据苗蚜和伏蚜自然天敌控制作用不同,制定合理的保护利用自然天敌的策略。     

小麦不同品种上麦蚜及其天敌的数量变动

试验结果表明小麦品种 (系 )的抗性对麦蚜种群数量影响很大 ,百株蚜量随着小麦品种抗性增强而下降。而同一小麦品种对不同种蚜虫的抗性存在质的差异 ,铭贤 1 69品种 ,蚜高峰期百株蚜量麦长管蚜 63 0头 ,禾谷缢管蚜只有 1 1 5头 ,两者相差 5 5倍。另一方面 ,小麦品种抗性对麦田天敌的种群数量影响不大 ,而对天敌的发生期有些影响。因此 ,小麦品种抗性、天敌对麦蚜的自然控制能力 ,可把小麦中后期的蚜虫虫口密度控制在经济损失允许水平之下。     

应用罩笼法定量评价天敌对麦蚜的控害作用

【目的】定量分析麦田自然天敌对麦蚜的控制作用。【方法】系统调查和罩笼接虫法。【结果】龟纹瓢虫Propylaea japonica Thunberg是麦蚜的主要天敌。在麦蚜发生平稳期、盛发期、消退期,自然天敌对麦蚜有稳定的控制作用,控害指数分别为35%、42%和32%。【结论】在制定麦蚜的防治策略时,应充分考虑自然天敌的控害作用,加强对自然天敌的保护利用。     

Dispersal of aphids, whiteflies and their natural enemies under photoselective nets

Integrated Pest Management of insects includes several control tactics, such as the use of photoselective nets, which may reduce the flight activity of insects. Limiting the dispersal of pests such as aphids and whiteflies is important because of their major role as vectors of plant viruses, while a minor impact on natural enemies is desired. In this study, we examined for the first time the dispersal ability of three vector species, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae) and Myzus persicae (Sulzer) (Hemiptera: Aphididae), in cages covered with photoselective nets. Contrary to the results obtained with aphids, the ability of the whitefly B. tabaci, to reach the target plant was reduced by photoselective nets. In a second set of experiments, the impact of UV-absorbing nets on the visual cues of two important predator species, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), was evaluated. The anthocorid was caught in higher numbers in traps placed under regular nets, whereas the mites preferably chose environments in which the UV radiation was attenuated. We have observed a wide range of effects that impedes generalization, although photoselective nets have a positive effect on pest management of whiteflies and aphids under protected environments.     

Spatial scale of benefits from adjacent woody vegetation on natural enemies within vineyards

Abundance of predators in crops can be increased by augmenting the adjacent non-crop vegetation, with associated environmental benefits from reduced chemical inputs and landscape conservation. Fine-scale spatial analysis is required to assess the extent to which non-crop benefits extend into farmed areas. We used explicit spatial mapping to investigate benefits of woody vegetation in two vineyards. The abundance of canopy-dwelling predators and predation/parasitism rates was measured at two vineyards with woody vegetation on one margin. Grids were sampled monthly across two summer growing seasons and stability of spatial patterns determined for consecutive months for each season and between seasons. At these two locations small parasitoids and several species of ladybird beetles from the vine canopy exhibited spatial patterning, with regions of high and low abundance and activity, aggregated in rows near to woody vegetation. Aggregations varied in temporal stability, with some persisting throughout the season. When predation and parasitism of sentinel eggs of a moth pest were non-randomly distributed, levels were higher in vine rows closer to the woody vegetation and significantly associated with a known egg parasitoid and ladybird beetles. This study demonstrated predators and parasitoids had non random and stable distributions at two vineyards. Increased abundance of both Coccinellidae and parasitoids was seen over similar distances: extending approximately 40 m from the vegetated edge. Increase in parasitism and predation extended a similar distance in from the vegetation. These results suggest management of vineyards where non-crop vegetation can be used to increase numbers and impact of beneficials, with recommendations for planting woody vegetation a minimum of 50 m from vineyard edges.     

Observations on the number of cereal aphids on the soil in relation to aphid density in winter wheat

The numbers of cereal aphids on the soil surface was assessed by soil samples and by counting the numbers captured in pitfall traps. A relationship was found by both methods between the density of aphids on the plants and the numbers of aphids on the soil. This relationship indicated that a higher proportion of the aphid population was on the soil surface at the lower densities on the plant. Reasons for this relationship are suggested and discussed.     

Cascade effects of crop species richness on the diversity of pest insects and their natural enemies

Understanding how plant species richness influences the diversity of herbivorous and predatory/parasitic arthropods is central to community ecology.We explore the effects of crop species richness on the diversity of pest insects and their natural enemies.Using data from a four-year experiment with five levels of crop species richness,we found that crop species richness significantly affected the pest species richness,but there were no significant effects on richness of the pests’natural enemies.In contrast,the species richness of pest insects significantly affected their natural enemies.These findings suggest a cascade effect where trophic interactions are strong between adjacent trophic levels,while the interactions between connected but nonadjacent trophic levels are weakened by the intermediate trophic level.High crop species richness resulted in a more stable arthropod community compared with communities in monoculture crops.Our results highlight the complicated cross-trophic interactions and the crucial role of crop diversity in the food webs of agro-ecosystems.     

Effects of feeding position of the aphids Sitobion avenae and Metopolophium dirhodum on wheat yield and quality

The effects of feeding site of Sitobion avenae and Metopolophium dirhodum on grain weight, number and nitrogen content were investigated in the laboratory and in the field. When the latter species was confined to particular leaves in a growth room, grain weight reductions occurred only when the aphid fed on the flag leaf; reductions in percentage grain protein, but not grain weight, followed lower leaf feeding. Leaves which had borne aphids had a higher proportion of nitrogen at death than control leaves, but this explained little of the shortfall in grain nitrogen, which was mainly due to direct removal during aphid feeding. Multiple regressions of grain weight on aphid species/feeding site in the field confirmed the lack of grain weight effects when lower leaves were colonised; because grain size was greatly reduced by aphid feeding, percentage grain nitrogen increased with increasing aphid density in one cultivar and in others was unchanged. Successive comparison of control grain weights with those from tillers bearing an increasing range of aphid densities resulted in a significant reduction in weight with tillers bearing 21 to 25 aphid units on their ear and flag leaf combined, one unit comprising one adult or fourth-instar aphid or three of earlier instars. These and other factors affecting the nature and extent of cereal aphid damage are discussed.     

Biological control of aphids in the presence of thrips and their enemies

Generalist predators are often used in biological control programs, although they can be detrimental for pest control through interference with other natural enemies. Here, we assess the effects of generalist natural enemies on the control of two major pest species in sweet pepper: the green peach aphid Myzus persicae (Sulzer) and the western flower thrips Frankliniella occidentalis (Pergande). In greenhouses, two commonly used specialist natural enemies of aphids, the parasitoid Aphidius colemani Viereck and the predatory midge Aphidoletes aphidimyza (Rondani), were released together with either Neoseiulus cucumeris Oudemans, a predator of thrips and a hyperpredator of A. aphidimyza, or Orius majusculus (Reuter), a predator of thrips and aphids and intraguild predator of both specialist natural enemies. The combined use of O. majusculus, predatory midges and parasitoids clearly enhanced the suppression of aphids and consequently decreased the number of honeydew-contaminated fruits. Although intraguild predation by O. majusculus on predatory midges and parasitoids will have affected control of aphids negatively, this was apparently offset by the consumption of aphids by O. majusculus. In contrast, the hyperpredator N. cucumeris does not prey upon aphids, but seemed to release aphids from control by consuming eggs of the midge. Both N. cucumeris and O. majusculus did not affect rates of aphid parasitism by A. colemani. Thrips were also controlled effectively by O. majusculus. A laboratory experiment showed that adult predatory bugs feed on thrips as well as aphids and have no clear preference. Thus, the presence of thrips probably promoted the establishment of the predatory bugs and thereby the control of aphids. Our study shows that intraguild predation, which is potentially negative for biological control, may be more than compensated by positive effects of generalist predators, such as the control of multiple pests, and the establishment of natural enemies prior to pest invasions. Future work on biological control should focus on the impact of species interactions in communities of herbivorous arthropods and their enemies.