Determination the population trends of cereal aphids and associated parasitoids by yellow sticky traps with reference to aphid management on wheat

Population trends of cereal aphids and their associated parasitoids inhabiting wheat plantations were monitored by yellow sticky traps. The identified aphids exhibited one seasonal peak for each and were found to be active during the first half of March. Data revealed that, Rhopalosiphum padi L peak occurred one week later than both of Schizaphis graminum (Rondani) and Rhopalosiphum maidis (Fitch). The numbers of aphid complex was recorded more at 90 than at 30 and 60 cm height. Hymenopterous parasitoids activity is synchronised with aphid species, whereas they appeared in small numbers at early and late wheat season and showed their peak on March, with a positive correlation coefficient with aphid populations. The tested compounds (Karate, Biscaya, Match 5% EC, Tracer 24% SC and Neem Azal T/S) showed 100% reduction in aphid numbers after 24 h post application. However, the general reduction percentages indicated 99.31 > 98.32 > 97.97 > 97.06 > 95.66%, by using the abovementioned compounds, respectively.     

The effect of introducing the aphid-pathogenic fungus Erynia neoaphidis into populations of cereal aphids

The aphid-pathogenic fungus Erynia neoaphidis, as dried fungus-infected aphids, was applied to caged plots of winter wheat infested with cereal aphids at two sites, one in Hertfordshire and the other in Hampshire, in 1983. In each trial, the fungus became established in the aphid populations in the treated plots even though conditions were drier than average and therefore sub-optimal for fungus spread. Treatment applied in the third week of June increased the proportion of infected aphids more than that applied two weeks later at one site, and the early application was the only treatment to have an obvious effect at the other. In spite of the observed effect of treatments on the proportion of infected aphids, the fungus failed to reduce the numbers of aphids relative to those in untreated plots, chiefly because in these plots many aphids were killed by fungi of the same species as that introduced and other related species from natural sources. Artificial introduction of E. neoaphidis acts too slowly and unpredictably to be likely to form a practical alternative to conventional insecticides for cereal aphid control.     

Mapping resistance to cereal aphids in barley

 A set of 150 doubled-haploid (DH) barley (Hordeum vulgare L.) lines derived from the cross of Harrington/TR306 was used to determine the number and chromosomal location of quantitative trait loci (QTLs) controlling resistance to cereal aphids. The experiments were conducted under natural infestation in the field during two growing seasons: 1994 and 1995. Aphid resistance was measured by counting the number of aphids per plot. Counts were made on a weekly basis. Each year at the time of maximum aphid density there was an obvious difference in reaction between the parental genotypes. The DH lines showed continuous variation for aphid density. Simple interval mapping and simplified composite interval mapping revealed that the principal QTL determining cereal aphid resistance is on the distal region of the short arm of chromosome 1. This aphid-resistance QTL is linked with a heading-date QTL. At the time of highest aphid infestation, this QTL accounted for 31% and 22% of the total variance of aphid density in 1994 and 1995, respectively. A QTL on chromosome 5 was also detected but only by simplified composite interval mapping. However, the largest consistent effect was due to the QTL on the short arm of chromosome 1. This QTL may be a useful target for marker-assisted selection for adult plant cereal aphid resistance in barley. Received: 10 September 1996/Accepted: 11 October 1996     

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.     

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.     

The influence of azadirachtin on the feeding behaviour of cereal aphids and slugs

The probing behaviour of Rhopalosiphum padi (L.) and Sitobion avenae (F.) and the feeding behaviour of several slug species, (Deroceras reticulatum (Müller), Arion distinctus Mabille, Agriolimax caruanae Pollonera, Maximus sp.) were assessed on seedlings of winter barley (Hordeum marinum) treated with different concentrations of azadirachtin. Settling behaviour of both aphid species was strongly biased towards the untreated seedlings or those treated with low concentrations of azadirachtin. Concentrations of <500 ppm were effective with topical application and probing activity was reduced for at least 4 days after application. Systemic activity of azadirachtin against cereal aphids was also demonstrated. Feeding behaviour of the slug species, as seen by the amount of leaf eaten compared to the controls, was not affected by the presence of azadirachtin at those concentrations which deterred aphids from feeding. The relevance of these results to crop protection is discussed.     

Interference between parasitoids [Hym.: Aphidiidae] and fungi [Entomophthorales] attacking cereal aphids

In field populations of cereal aphids parasitism levels declined through the season as fungal infection increased. In laboratory trials the fungusErynia neoaphidis Remaudiere & Hennebert took 3 to 4 days to kill the rose-grain aphid,Metopolophium dirhodum (Walker), whereas the parasitoidAphidius rhopalosiphi De Stefani-Perez took 8 to 9 days at 20°C. When aphids were infected by the fungus less than 4 days after being parasitized the parasitoids were prevented from completing their development. Conversely, when infection occurred more than 4 days after parasitization development of the fungus was significantly impaired. There was no histological evidence that the fungus invaded the tissues of the parasitoid when both attacked the same aphid. Interference between parasitoids and fungal pathogens must be taken into account when estimating the impact of these mortality agents on pest populations.     

Rates of consumption of cereal aphids by some polyphagous predators in the laboratory

The consumption rates of nine species of Carabidae and five species of Staphylinidae which feed on the aphid Sitobion avenae (F.) were studied under conditions of surplus food in the laboratory. The mean daily consumption of aphids was between 2.5% and 45.6% of the predator species' mean body weight; the lowest values were for large Carabidae and the highest for small Staphylinidae. Separate significant positive relationships were found between the mean total weight of aphids consumed per day, and the mean weight of the adult of the carabid and staphylinid species at each temperature. A re-evaluation of published data also showed this. The slopes of the regression lines were steeper for the Staphylinidae than for the Carabidae and possible reasons are given. The regression equations could be used in simulation models to determine the maximum possible effects of these beetles on aphid populations.

---

Résumé La consommation de Sitobion avenae F. par 9 espèces de Carabidae et de 5 de Staphylinidae a été examinée au laboratoire en condition de surapprovisionnement. Les expériences ont été répétées dans 4 conditions de températures variables caractérisées par des moyennes de 12°3, 16°6, 20°6 et 23°6. Les poids moyens de pucerons consommés variaient entre 2,5% et 45,6% du poids des prédateurs; les valeurs les plus faibles correspondant aux gros carabes et les plus élévées aux petits staphylins.Les différences entre sexes étaient vraisemblablement dues au dimorphisme pondéral. Une relation significative et positive entre le poids moyen de pucerons consommés et le poids moyen du coléoptère a été mise en évidence tant pour les carabes que les staphylins à toutes les températures (Fig. 1, Tableau 2). Cette relation ressort aussi d'une réévaluation des données publiées. L'utilisation de formules de régression dans des modèles de simulation permettra de prédire les effets des carabes et des staphylins sur les populations de pucerons dans ces conditions optimales.

     

Assessment of the relative impact of different natural enemies on population dynamics of the grain aphid Sitobion avenae in the field

1. A detailed population dynamics model was devised to provide a tool for integrated pest management against the cereal aphid Sitobion avenae on winter wheat. 2. This model allowed investigation of the relative impact of different natural enemies on aphid population dynamics. 3. The output of the model was compared with a set of data collected in the western part of France from 1976 to 1986. 4. Fungal diseases accounted for 75% of the reduction in peak aphid density and were the key factor acting on aphid dynamics in this region. 5. This study highlights the importance of detailed population dynamics modelling of keystone species, like aphids, for elucidation of the relations between the keystone species and other species associated in the ecosystem.     

Tolerance of antibiotic and susceptible cereal seedlings to the aphids Metopolophium dirhodum and Rhopalosiphum padi

Some cereal seedlings exhibit antibiotic and antixenotic resistance to the aphids Metopolophium dirhodum (Walker) and Rhopalosiphum padi (L.), because the seedlings contain hydroxamic acids or gramine. The association between tolerance to aphids and aphid antibiosis was investigated for three cereals, Dollarbird wheat Vulcan wheat and Yagan barley. The dry biomass gained by the aphids and the simultaneous reduction in the biomass of the plants (biomass conversion ratio) quantified tolerance. Biomass production and the density dependence of biomass production by the aphids quantified antibiosis more effectively than fecundity. Vulcan wheat, which has more hydroxamic acid than Dollarbird wheat showed the highest level of antibiosis, and the barley was not antibiotic for either aphid. The biomass conversion ratio was a constant; the biomass of an infested plant was reduced by 3 mg for each mg of aphid biomass gained, regardless of aphid species, plant cultivar, or aphid density. The three plants showed no differential tolerance to the aphids, and therefore tolerance is not associated with antibiosis in this case.     

Density dependence in cereal aphid populations

Long sequences of data on the incidence of cereal aphids from five European countries were analysed for evidence of density dependent processes occurring between years. Using a randomisation test (Pollard, Lakhani & Rotheray, 1987), density dependence was revealed in all (16) population censuses of Metopolo-phium dirhodum , 60% of Rhopalosiphum padi censuses (10 of 17) but only 25% of Sitobion avenae population censuses (4 of 16). Correcting for density independent effects of weather revealed the existence of significant direct density dependence in some populations censuses where it was previously undetected. The implications of density dependence in cereal aphid populations are considered.     

Observation on the initial inoculum source and dissemination of Entomophthorales-caused epizootics in populations of cereal aphids

A total number of 1092 migratory alates were trapped from air in wheat grown area of Yuanyang County, Henan Province from early April through May 2002 in order to confirm the source and dissemination of entomophthoralean inocula to cause epizootics of cereal aphids. Those included 415 Sitobion avenae, 642 Rhopalosiphum padi, 22 Metopolophium dirhodum, and 13 Schizaphis graminum. The trapped alates were daily collected and individually reared for 7 days on wheat plants in laboratory. Of those 341 alates died of fungal infection, taking 31.2% in the trapped alates. These included 224 S. avenae, 106 R. padi, 8 M. dirhodum, and 3 S. graminum. Deaths of all infected alates occurred during the first 5 days and 78.9% of the deaths occurred within the first 3 days. Individual examination under microscope proved that all deaths were attributed to entomophthoralean fungi. Of those Pandora neoaphidis accounted for 84.6%, Conidiobolus obscurus for 9.9%, and Entomophthora planchoniana for 5.5%. Four alate deaths died of cross infection of P. neoaphidis and C. conidiobolus. Based on the high infection rate of the migratory alates trapped from air and the field occurrence of epizootics in populations of cereal aphids during the trapping period, Entomophthorales-caused epizootics were likely disseminated by infected alates through their flight and colonization. This makes it reasonable to interpret worldwide distribution of aphid epizootics, particularly caused by P. neoaphidis that has no resting spores discovered.     

The role of large-scale spatially explicit and small-scale localized processes on the population dynamics of cereal aphids

A field-scale study of the spatially explicit interaction between the carabid Poecilus cupreus Linnaeus, and two common aphid species (Sitobion avenae (Fabricius) and Metopolophium dirhodum (Walker)) in winter wheat was conducted. All three species showed considerable spatial pattern at the field scale. Activity-density of P. cupreus was an order of magnitude higher in the central part of the field compared to its periphery. Where P. cupreus activity-density was highest, S. avenae and M. dirhodum population peaks were delayed. Additionally, in the case of M. dirhodum, lower maximum counts were evident where P. cupreus activity-density was highest. An analysis of the movement of individual P. cupreus using release-recapture indicated that those beetles within the centre of the field exhibited reduced displacement, which may have caused the generation or maintenance of spatial pattern. Crop density was also measured throughout the field. Although crop density had no large-scale spatial pattern, its variability at the small-scale was consistent with an influence on aphid population dynamics. This study demonstrates empirically that both large-scale spatially explicit and small-scale localized processes influenced aphid population dynamics simultaneously.     

The influence of clone and morph on the parameters of intrinsic rate of increase in the cereal aphids Sitobion avenae and Rhopalosiphum padi

This study aimed at evaluating the influence of intrinsic factors (clone, morph) on the parameters of the intrinsic rate of increase of Sitobion avenae (F.) and Rhopalosiphum padi (L.). For each species, apterous and alate exules of three clones originating from French oceanic regions were compared at 20 °C.The clonal factor had a significant effect on both time from birth until onset of reproduction (TBR) and intrinsic rate of increase (r). This effect was lower than that of the morph. Moreover, in the case of R. padi, a strong clone-morph interaction was observed.Both apterous and alate morphs were shown to have a higher rate of increase in R. padi than in S. avenae.Various models were fitted to aphid daily rate of reproduction. Both types of model and quality of fit depended mainly on the morph.

---

Résumé Cette étude a eu pour but d'évaluer l'importance de facteurs intrinsèques (clone et morphe) sur les paramètres du taux d'accroissement de Sitobion avenae (F.) et Rhopalosiphum padi (L.).Pour chaque espèce, trois clones originaires de régions océaniques françaises ont été comparés à 20 °C pour les morphes exules ailés et exules aptères.L'effet du clone est significatif sur l'âge reproducteur (durée comprise entre la naissance du puceron et le début de sa phase de reproduction) et sur le taux intrinsèque d'accroissement naturel. Il est plus faible que celui du morphe avec lequel il intéragit dans le cas de R. padi.Les différences interspécifiques relevées mettent en évidence les capacités d'accroissement supérieures de R. padi par rapport à celles de S. avenae, dans le cas des ailés comme dans celui des aptères.Enfin, différents modèles ont été appliqués aux données de reproduction journalière des pucerons. Le type et la qualité des ajustements varient essentiellement en fonction du morphe.

     

Forecasting migration of cereal aphids (Hemiptera: Aphididae) in autumn and spring

The migration of cereal aphids and the time of their arrival on winter cereal crops in autumn and spring are of particular importance for plant disease (e.g. barley yellow dwarf virus infection) and related yield losses. In order to identify days with migration potentials in autumn and spring, suction trap data from 29 and 45 case studies (locations and years), respectively, were set‐off against meteorological parameters, focusing on the early immigration periods in autumn (22 September to 1 November) and spring (1 May to 9 June). The number of cereal aphids caught in a suction trap increased with increasing temperature, global radiation and duration of sunshine and decreased with increasing precipitation, relative humidity and wind speed. According to linear regression analyses, the temperature, global radiation and wind speed were most frequently and significantly associated with migration, suggesting that they have a major impact on flight activity. For subsequent model development, suction trap catches from different case studies were pooled and binarily classified as days with or without migration as defined by a certain number of migrating cereal aphids. Linear discriminant analyses of several predictor variables (assessed during light hours of a given day) were then performed based on the binary response variables. Three models were used to predict days with suction trap catches ≥1, ≥4 or ≥10 migrating cereal aphids in autumn. Due to the predominance of Rhopalosiphum padi individuals (99.3% of total cereal aphid catch), no distinction between species (R. padi and Sitobion avenae) was made in autumn. As the suction trap catches were lower and species dominance changed in spring, three further models were developed for analysis of all cereal aphid species, R. padi only, and Metopolophium dirhodum and S. avenae combined in spring. The empirical, cross‐classification and receiver operating characteristic analyses performed for model validation showed different levels of prediction accuracy. Additional datasets selected at random before model construction and parameterization showed that predictions by the six migration models were 33–81% correct. The models are useful for determining when to start field evaluations. Furthermore, they provide information on the size of the migrating aphid population and, thus, on the importance of immigration for early aphid population development in cereal crops in a given season.     

Comparison of the effect of hydroxamic acids from wheat on five species of cereal aphids

Feeding behaviour of five species of cereal aphids in wheat seedlings differing in hydroxamic acid (Hx) levels, was monitored via electrical penetration graphs (EPG). Aphid species could be grouped as sensitive to the feeding deterrent effect of Hx in the seedlings (Rhopalosiphum padi, Schizaphis graminum, Sitobion avenae, andMetopolophium dirhodum) or insensitive to them (Rhopalosiphum maidis). However, when feeding behaviour was studied in artificial diets containing Hx, all species were equally sensitive to Hx. The behavour ofR. maidis was further compared with that ofR. padi through detailed EPG analysis. It was found that the insensitivity ofR. maidis to Hx in seedlings may be due to a feeding strategy avoiding contact with the compounds by decreasing the number of cellular punctures in live tissues other than sieve elements during its way to the phloem.     

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。     

The influence of nitrogen fertiliser on the population development of the cereal aphids Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.) on field grown winter wheat

The effect of nitrogen fertiliser on populations of the cereal aphids Sitobion avenae and Metopolophium dirhodum on winter wheat was investigated in a three year field experiment. Naturally occurring aphid populations were monitored on three nitrogen treatments; none, nitrogen application using Canopy Management guidelines (130–210 kg ha^-1) and conventional practice (190 kg ha^-1). Inoculations of laboratory reared S. avenae were used to enhance field populations on half the plots. Natural populations of M. dirhodum remained below the current UK spray threshold level of two-thirds of shoots infested at the start of flowering, or five aphids per shoot in all years, whilst populations of S. avenae exceeded the threshold in all years. The response of the two species to nitrogen differed. Significantly higher populations of M. dirhodum were recorded in both treatments which received nitrogen in all years, whilst the response of S. avenae varied between years. In 1994 and 1995 when environmental conditions favoured aphid development, higher populations were recorded in the two treatments which received nitrogen. In 1993 when high rainfall created unfavourable conditions, higher populations were recorded in the plots receiving no nitrogen. Differences in peak density and cumulative aphid index of S. avenae resulted from differences in the rate of population increase between ear emergence and peak density on the different treatments. Populations prior to ear emergence were higher in the plots which received nitrogen but the differences were not statistically significant. There was no evidence of a difference in the timing of population decline in the different treatments. In 1993 higher levels of infection by entomopathogenic fungi were observed in all treatments. Significantly higher levels of infection were recorded in the treatments receiving nitrogen, which may have accounted for the lower S. avenae populations recorded. It is possible that the larger canopies recorded in these treatments produced conditions which favoured infection by fungi, thereby limiting aphid population growth. The results indicate that application of nitrogen increases natural populations of M. dirhodum, and under favourable conditions, populations of S. avenae. However, in suboptimal climatic conditions, the application of nitrogen fertiliser can lead to lower populations of 5. avenae. The data also suggest that there is no consistent difference between a conventional and Canopy Managed approach to nitrogen fertiliser use in terms of the risk of infestation by cereal aphids.     

Natural enemy ravine revisited: the importance of sample size for determining population growth

Abstract. 1. The population growth of three aphid species, Metopolophium dirhodum (Walker), Rhopalosiphum padi (L.), and Sitobion avenae (F.), on winter wheat, was analysed by regression. The calculations were based on censuses of aphids made in 268 plots at 3- or 7-day intervals for 10 years on leaves and 6 years on ears. The calculations were made separately for each plot each year, then repeated on the pooled data from all plots monitored in a year.
2. At the level of individual plots, no population growth was detected at very low densities. At high densities, the populations grew exponentially and the growth rates did not decrease with increasing aphid density.
3. Significant growth was always detected in the pooled data. These growth rates decreased significantly at the highest densities. Field estimates of the intrinsic rate of increase derived from these data ranged from 0.010 to 0.026 for M. dirhodum , 0.0071–0.011 for R. padi , and 0.00078–0.0061 and 0.0015–0.13 for S. avenae , on leaves and ears respectively .
4. The apparent lack of growth in the individual plots at low densities is attributable to small sample size. It is concluded that the natural enemy ravine in the population dynamics of cereal aphids, identified by Southwood and Comins (1976), is a consequence of low population densities at which population increase is undetectable unless very large samples are taken.