The spatial and temporal distribution of the grain aphid Sitobion avenae in winter wheat

The spatial and temporal distribution of the grain aphid Sitobion avenae F. (Homoptera: Aphididae) was studied within a field of winter wheat during the summer of 1996. Sampling was done using four nested grids comprising 133 locations. Analysis by Taylor's power law gave results typical for insect populations. Analysis by SADIE (Spatial Analysis by Distance Indices) showed spatial pattern due to edge effects and sampling scale, and positive but mild spatial association, although spatial patterns were ephemeral. Reasons for these findings and the implications for integrated crop management are discussed.     

Effects of DIMBOA levels in wheat on the susceptibility of the grain aphid (Sitobion avenue) to deltamethrin

The effects of DIMBOA in cultivars of wheat on aphid antibiosis and tolerance to the insecticide deltamethrin were investigated for the aphid Sitobion auenae. Over 48 hours the mean relative growth rate differed significantly between nymphs of S. auenae reared on wheat cultivars containing different levels of DIMBOA. Nymphs on the resistant cv. Altar showed a significantly greater susceptibility to deltamethrin, with nearly a three-fold increase in the relative toxicity of deltamethrin, compared with the susceptible cv. Dollarbird. The LC₅₀, adjusted for weight, was reduced by 91% for nymphs reared on the high DIMBOA cultivar. The potential for the enhancement of predation under a reduced pesticide régime is discussed in relation to this research.     

Field manipulation of populations of individual staphylinid species in cereals and their impact on aphid populations

Abstract.

• 1 Four species of staphylinids were caged separately on wheat and their effect on the population development of the grain aphid, Sitobion avenae (F.), was investigated over two seasons.
• 2 A novel field cage design was used to exclude all but the staphylinid species under investigation.
• 3 Predator effects were compared with total-exclusion cages in which all predators and parasitoids were kept out.
• 4 During a high-density phase of aphid population development only Philonthus cognutus (Stephens) significantly influenced aphid population numbers.
• 5 At low aphid densities, Tachyporus obtusus (L.), T.chrysomelinus (L.) and P.cognatus reduced aphid population levels.
• 6 The experiments showed that Tachyporus spp. can reduce the numbers of cereal aphids prior to the exponential phase of aphid population increase and that P.cognatus causes some reduction at both the stages of aphid population growth investigated.

     

农业景观结构对麦蚜寄生蜂群落组成的影响

麦蚜是中国北方小麦上最重要的害虫之一,既能直接刺吸危害也可传播多种病毒,但麦蚜通常的危害期只有2～3个月。随着现代农业与设施农业的发展,农业景观结构发生了巨大的改变,整个麦蚜寄生蜂群落也随之发生了显著的变化。经典假说认为复杂的农业景观能够维持局部的物种多样性及种间关系,也能够维持更大的天敌资源。作者在4种不同的麦田景观类型下研究了麦蚜及寄生蜂的群落结构,发现简单农业景观与复杂农业景观中寄生蜂寄生率与多样性差异不显著,但初寄生蜂在800m2左右的生境面积中寄生率与多样性最高,重寄生蜂却并没有表现出这种分布,而在更大的生境中重寄生率与多样性更高。研究结果表明:1)生境面积是影响麦蚜及寄生蜂群落的重要因子,2)简单农业景观与复杂农业景观下麦蚜及寄生蜂群落多样性差异不显著,3)一定程度的生境破碎化能够促进初寄生蜂的种群而抑制重寄生蜂的种群,但高度的生境破碎化会同时抑制2种寄生蜂的种群。     

Feeding behaviour of the staphylinid beetle Tachyporus hypnorum in relation to its potential for reducing aphid numbers in wheat

Aphid consumption by larval and adult Tachyporus hypnorum (Coleoptera: Staphylinidae) in different reproductive states was compared under laboratory conditions. Post-overwintering (spring/summer) adults had a higher consumption rate of first/second instar Sitobion avenae (Hemiptera: Aphididae) than did overwintering adults. Choice experiments incorporating Isotoma viridis (Collembola: Isotomidae) and Sciara thomae (Diptera: Mycetophilidae) as alternative prey items showed that T. hypnorum had a strong preference for aphids at a range of prey frequencies. Numbers of aphids consumed were reduced when leaves infected with Erysiphe graminis f.sp. tritici (powdery mildew of wheat) were offered to beetles with aphids in choice experiments. Behavioural studies of adult T. hypnorum showed that foraging rates on wheat plants increased with increasing amounts of both mildew and aphids on plants. Feeding upon only the conidia of E. graminis was observed. Results are discussed in relation to previous data derived from gut dissection, to a field survey of alternative foods and to the phenology of T. hypnorum in relation to that of aphids in the wheat crop.     

The economics of reduced-rate insecticide applications to control aphids in winter wheat

Applications of pirimicarb and fenvalerate at full-rate and at a range of reduced dosages were applied on fields of winter wheat between 1983 and 1988 in West Germany. The relative effects of these treatments on the control of cereal aphids varied according to the growth stage at which spraying took place and the size of the aphid populations. The economic profitability of these treatments depended on the extent of post-treatment recovery of the aphid populations, the cost of control and the crop value. Under certain circumstances the high efficiencies of commonly-used insecticides at full dose-rate are not necessary to gain effective aphid control economically; a better return can be made by reducing the quantity of active ingredient per hectare.     

Jasmonate- and salicylate-induced defenses in wheat affect host preference and probing behavior but not performance of the grain aphid,Sitobion avenae

Jasmonate and salicylatemediated signaling pathways play significant roles in induced plant defenses, but there is no sufficient evidence for their roles in monocots against aphids. We exogenously applied methyl jasmonate （MeJA） and salicylic acid （SA） on wheat seedlings and examined biochemical responses in wheat and effects on the grain aphid, Sitobion avenae （Fab.）. Application of MeJA significantly increased levels of wheat＇s polyphenol oxidase, peroxidase and proteinase inhibitor 1, 2 and 6 days after treatment. In twochoice tests, adult aphids preferred control wheat leaves to MeJA or SA treated leaves. Electrical penetration graph （EPG） recordings of aphid probing behavior revealed that on MeJAtreated plants, the duration of aphid＇s first probe was significantly shorter and number of probes was significantly higher than those on control plants. Also total duration of probing on MeJAtreated plants was significantly shorter than on control plants. Total duration of salivation period on SAtreated plants was significantly longer, while mean phloem ingestion period was significantly shorter than on control plants. However, no significant difference in total duration of phloem sap ingestion period was observed among treatments. The EPG data suggest that MeJAdependent resistance factors might be due to feeding deterrents in mesophyll, whereas the SAmediated resistance may be phloembased. We did not observe any significant difference of MeJA and SA application on aphid development, daily fecundity, intrinsic growth rate and population growth. The results indicate that both MeJA and SAinduced defenses in wheat deterred S. avenae colonization processes and feeding behavior, but had no significant effects on its performance.     

Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

Diversity,frequency, and geographic distribution of facultative bacterial endosymbionts in introduced aphid pests

Facultative bacterial endosymbionts in insects have been under intense study during the last years. Endosymbionts can modify the insect's phenotype, conferring adaptive advantages under environmental stress. This seems particularly relevant for a group of worldwide agricultural aphid pests, because endosymbionts modify key fitness‐related traits, including host plant use, protection against natural enemies and heat tolerance. Aimed to understand the role of facultative endosymbionts on the success of introduced aphid pests, the distribution and abundance of 5 facultative endosymbionts (Hamiltonella defensa, Regiella insecticola, Serratia symbiotica, Rickettsia and Spiroplasma) were studied and compared in 4 cereal aphids (Sitobion avenae, Diuraphis noxia, Metopolophium dirhodum and Schizaphis graminium) and in the pea aphid Acyrthosiphon pisum complex from 2 agroclimatic zones in Chile. Overall, infections with facultative endosymbionts exhibited a highly variable and characteristic pattern depending on the aphid species/host race and geographic zone, which could explain the success of aphid pest populations after their introduction. While S. symbiotica and H. defensa were the most frequent endosymbionts carried by the A. pisum pea‐race and A. pisum alfalfa‐race aphids, respectively, the most frequent facultative endosymbiont carried by all cereal aphids was R. insecticola. Interestingly, a highly variable composition of endosymbionts carried by S. avenae was also observed between agroclimatic zones, suggesting that endosymbionts are responding differentially to abiotic variables (temperature and precipitations). In addition, our findings constitute the first report of bacterial endosymbionts in cereal aphid species not screened before, and also the first report of aphid endosymbionts in Chile.     

两类不同玉米田蚜虫发生动态数学模型与空间分布型测定

蚜虫是我国各地玉米植株上的重要刺吸类害虫。为了进一步阐述该虫的发生与环境之间的关系,以及其在转基因抗性玉米上的空间分布,本文在田间系统调查蚜虫种群动态的基础上,使用多元回归分析法、Iwao回归分析法和5种常用指标参数法,探明了玉米田蚜虫发生与环境因素之间相关的数学模型,以及在常规玉米和抗性玉米植株上的空间分布。结果表明：江苏扬州地区两类不同玉米植株上发生的蚜虫以玉米蚜为主,玉米蚜虫的发生与当日最低气温关系最密切;玉米蚜虫在玉米植株上部的分布数量可达70%~80%,其全株玉米上的蚜量（y）与玉米植株上部1/3上的蚜量（x）关系为y=1.33x;玉米蚜虫在植株上的分布为聚集分布,其聚集由自身特性和环境因素共同确定。本研究为开展转基因玉米田蚜虫的测报防控提供了重要依据。     

Northern Atlantic Oscillation effects on the temporal and spatial dynamics of green spruce aphid populations in the UK

1. The role of climate variability in determining the spatial and temporal patterns of numerical fluctuations is a central problem in ecology. The influence of the North Atlantic Oscillation (NAO) index on the population dynamics and spatial synchrony of the green spruce aphid Elatobium abietinum across the UK was shown. 2. Fifteen overlapping time series within the UK were analysed; we used nonparametric models for determining the feedback nonlinear structure and the climatic effects. The spatial synchrony of these populations and the relationship between synchrony and NAO was estimated. 3. From the 15 time series across the UK, 11 showed positive and significant NAO effects. In most of the cases the NAO effects were nonlinear showing strong negative effects of low values. The NAO variation improve the explained variance of the first-order feedback models in 14.5%; ranging from 0% to 48%. All data showed strong-nonlinear (concave) feedback structure. In most of the localities the explained variance by the first-order feedback was about 50-60%. 4. The spatial synchrony of the per capita growth rates and residuals is high across long distances for those populations affected by NAO. The correlation function predicts a spatial scale of synchrony of about 350-400 km for NAO influenced populations. 5. We think that simple population theoretical models describing the link between NAO fluctuations and green spruce aphid dynamics may be fundamental for predicting and simulating the consequences of different climatic scenarios of the future.     

The effects of nitrogen and fungicide on cereal aphid population development and the consequences for the aphid-yield relationship in winter wheat

In a field trial, done over two seasons, nitrogen and fungicide inputs to winter wheat were varied to obtain a range of yields to study the effects on aphid population development and the aphid-yield loss relationship. In the first year, the maximum density of Metopolophium dirhodum and total aphid index were significantly higher in the plots receiving the largest amount of nitrogen but there were few other consistent effects on aphid population development. In the second year there were no significant effects of either nitrogen or fungicide on aphid population development. Mean yields were high in 1987 and 1988 (7.0 and 8.5 t/ha respectively) with less than a 2 t/ha range in either year. There were no significant effects of aphids on yield in the first year but in the second, aphids caused a significant reduction. Damage per aphid unit did not change with increase in yield. The use of this approach in determining pest-yield loss relationships is discussed.     

Manipulating field margins to increase predation intensity in fields of winter wheat (Triticum aestivum)

The effectiveness of natural enemies to control pests can be enhanced through habitat manipulation. However, due to the differences in their ecology, generalist and specialist species may respond differently to the same manipulation. Moreover, interactions among natural enemies (i.e. cannibalism, intraguild predation, hyperparasitism) may complicate the assumption that a higher density of natural enemies would increase the level of biological control. We investigated the natural enemy guild composition and the predation rate along flower vs. grass margins at the edge of winter wheat (Triticum aestivum) fields in Denmark. Natural enemies were sampled by pitfall trapping and by suction sampling; predation intensity was measured using two different sentinel prey methods: artificial caterpillars made of plasticine, and sentinel aphid colonies. Specialist and generalist species responded differently to the two margin types: specialists (mostly parasitic wasps) were attracted by the flower margins, while generalists (ground beetles, rove beetles and spiders) were more active in grass margins. The number of artificial caterpillars attacked was significantly greater in grass margins (mean = 48.9%, SD = 24.3) than in flower margins (mean = 30.7%, SD = 17.4). We found a significant positive relationship between the number of artificial caterpillars attacked by chewing insects, and activity density for large (≥15 mm) ground beetles. Predation of sentinel aphids in wheat fields did not vary significantly in relation to margin type. Our results suggest that flowering margins may be beneficial for canopy‐active specialist natural enemies, but grassy margins are more useful for ground‐active generalist predators.     

Host suitability and thermal requirements of Lathromeris ovicida Risbec (Hymenoptera: Trichogrammatidae), an egg parasitoid of cereal stemborers in Africa

Factors affecting the bionomics of the trichogrammatid egg parasitoid Lathromeris ovicida and its association with the two sympatric scelionid egg parasitoids Telenomus busseolae and Telenomus isis were studied in the laboratory. The potential host species employed were the noctuids Sesamia calamistis and Sesamia botanephaga, and the pyralids Eldana saccharina and Mussidia nigrivenella. Using eggs of S. calamistis Hampson as hosts, the lower and upper thresholds for development were estimated at 14.8 and 34 °C, respectively. The percent parasitism, total progeny, and sex ratio decreased gradually from 42.0 to 10.2, from 56.4 to 10.8, and from 0.74 to 0.61, respectively, with host age. The intrinsic rate of increase and female fecundity was highest on the two noctuids, followed by E. saccharina and M. nigrivenella. Lathromeris ovicida preferentially attacked eggs already parasitised by either Telenomus busseolae or Telenomus isis. Thus, L. ovicida is probably a facultative hyperparasitoid.     

The effect of plant phenology on the induction of alatae and the development of populations of Metopolophium dirhodum (Walker), the rose-grain aphid, on winter wheat

In field experiments apterous Metopolophium dirhodum produced significantly more alatae when reared on mature plants (milky ripe stage) than on young plants. Nymphal and adult survival and relative growth rate were little affected by the developmental stage of the host plant. Relative growth rate and fecundity were strongly related to temperature. Laboratory experiments confirmed that the developmental stage of wheat had no significant effect on survival or relative growth rate of the aphids. However, laboratory grown plants did not produce the levels of alate production seen in field crops and in the field experiments. It is suggested that in investigations into the effects of the host plant on cereal aphids field grown plants should be used whenever possible. Alate production is proposed as the major plant induced factor affecting the development of M. dirhodum populations on wheat in the field. Alatae developed on mature plants even when the number of aphids was very low.     

The effect of reducing growth in winter wheat on the population dynamics of the grain aphid Sitobion avenae (F.)

1 The effect of reducing the growth of winter wheat on population size and development of the grain aphid Sitobion avenae was studied. 2 Automatic, mobile, crop shading devices, which reduced radiation comparable to levels found on a cloudy day, whilst minimizing other climatic changes, were used to reduce crop growth. Shading was applied between either GS 31 and 39 (1st node detectable → flag leaf ligule just visible) or GS 39 and 55 (flag leaf just visible → 50% of inflorescence emerged). 3 Sitobion avenae populations were initiated at GS 55 and highest populations were subsequently observed on plants shaded between GS 31 and 39. 4 Individual aphids confined within clip cages were observed to measure development from birth to adult moult, adult lifespan and fecundity. Results indicated that adult lifespan was shortest on plants shaded between GS31 and 39, whilst there were no differences in development time or fecundity. 5 Possible explanations for these observations are discussed.     

麦蚜和寄生蜂对农业景观格局的响应及其关键景观因子分析

大量研究表明多样性的农业景观格局能够影响蚜虫及寄生蜂的分布。本文利用并设计了两种尺度的麦田农业景观格局,依据麦蚜种群发生特点,分为迁入期、增长期与高峰期三个时期,论述了不同尺度下农业景观元素对麦蚜及寄生蜂系统的影响,通过逐步回归筛选了不同时期麦蚜及寄生蜂分布的关键景观元素,最后通过CANOCO软件模拟了麦蚜及寄生蜂的分布排序格局。结果表明不同景观因子对麦蚜及寄生蜂种群影响不同,迁入期两种尺度下裸地最有利于两种有翅蚜的迁飞入田,塑料大棚对有翅蚜种群的入田有抑制作用。增长期草地与林地生境对麦蚜种群增长率促进最大,塑料大棚同样抑制了麦蚜的种群增长率;但塑料大棚、草地与林地对蚜茧蜂的种群增长率有促进作用,非麦类作物生境对蚜茧蜂种群增长率抑制作用最大;草地与林地有利于重寄生蜂的种群增长率;高峰期裸地比例大的农业景观下麦蚜的最大种群密度较大,草地与林地对蚜茧蜂与重寄生蜂的最大种群密度均有促进作用。两种尺度下的研究结果一致。不同麦物种的对不同景观元素反应与形态学与生活史特征有关,而且景观结构中特定的植物种类、非作物植物的密度与物候期都可能影响寄生蜂群落的多样性与功能。     

Changes in the levels of plant total phenols and free amino acids induced by two cereal aphids and effects on aphid fecundity

Abstract:  Phenols and amino acids have previously been involved in the resistance of cereals to aphids. In the present study, the mean total concentrations of both compounds were quantitatively estimated from leaf-tissue samples collected at three growth stages (third, fifth and seventh leaf stages) from maize and barley seedlings and then correlated with the mean 7-day fecundity of Rhopalosiphum padi (L.) and Sitobion avenae (F.) (Homoptera, Aphididae) reared separately on the corresponding growth stages of each cereal. Results revealed an inverse correlation between the total concentration of each chemical in aphid-infested maize and barley plants and the fecundity of each aphid on every growth stage of the cereals. Moreover, R. padi led to an increase in total amino acids when reared on maize or barley without affecting the phenol concentration, while S. avenae induced a decrease in phenol levels but did not change the total amino acids on each growth stage of the plants. The significance of these results for understanding potential differences in requirements of cereal aphids for host selection and acceptance are discussed.