Characteristics of resistance to the grain aphid Sitobion avenue in winter wheat

Five stocks of winter wheat were resistant to S. avenae in glasshouse screening tests, where resistance was more evident in older than younger plants but different types of resistance were not separated. Antibiosis was measured from the growth and reproduction of caged individual aphids and antixenosis from the settling of adult aphids on detached leaf portions. Cvs Bounty, Rapier and Virtue were resistant due to antibiosis, whilst cv. Kador and line A4501-4E showed antixenosis. These and other differences indicated that these five wheat stocks probably include at least four distinct sources of resistance to S. avenae. The existence of different types of resistance could account for variability in the results of screening tests.     

A screen of worldwide wheat cultivars for hydroxamic acid levels and aphid antixenosis

In a screen of seedlings of a worldwide range of 47 cultivars of Triticum (mainly T. aestivum) the concentration of the hydroxamic acid DIMBOA ranged between 1 and 8 mmol/kg fresh wt. In a bioassay in which alatae of the aphid Sitobion avenae were released among replicated test seedlings, there were highly significant correlations between aphid ‘preference’ and DIMBOA levels in the seedlings. The value of these results in work leading to the production of aphid-resistant cultivars is discussed.     

The effect of hydoroxamic acid concentration at late growth stages of wheat on the performance of the aphid Sitobion avenae

From a previous worldwide screen of wheat cultivars as seedings, five were selected to encompass a wide concentraiton range of the hydroxaminc acid DIMBOA (0.99-8.07 mmol Kg ^-1 fr. wt). Compared with those in seedings, the concentrations of DIMBOA in flag leaves of the same cultivars were relatively low (0.06-0.87 mmol kg^-1 fr. wt). Concentraions of hydroxamic acids in whole ears at anthesis and the early milk stage were even lower, ranging from undetectable to 0.05 mmol kg^-1 fr. wt. The three-day mean relaive growth rate (MRGR) was determined for nymphs of Sitobion avenace on the flag leaf (GS 39) and on the ear (GS 60-60) of the five cultivars. No significant differences in MRGR were found between cultivatrs at the same growth stage, although MRGR was higher on ears on than on flag leaces. The results are discussed in realtion to the potential of hydroxamic acids in programmses aimed at breeding mature-plant aphid resistance into wheat cultivars.     

Temporal and spatial changes in aphid and parasitoid populations following applications of deltamethrin in winter wheat

The spatial and temporal effects of the pyrethroid insecticide, deltamethrin, on populations of cereal aphids and their primary parasitoids and hyperparasitoids were investigated in a large scale field experiment in winter wheat. Four hectare plots were treated at the recommended field concentration or a reduced concentration representing one twentieth of field rate. A control plot was left unsprayed. Invertebrate populations were sampled at sites within a grid layout covering the whole plots, enabling the use of geostatistical analysis. Hymenopteran populations were monitored using transparent sticky traps and suction sampling. Aphid populations were recorded by visual counts. Monitoring continued for 36 days after treatment. The full rate deltamethrin treatment resulted in initial reductions of aphid populations by 78%. Primary parasitoid and hyperparasitoid populations were reduced in suction samples by 90% and 47% respectively, when corrected for control fluctuations. The reduced deltamethrin concentration caused reductions of aphid, primary parasitoid and hyperparasitoid populations of 40, 60 and 54% respectively. Aphid population recovery over the full rate plot occurred slowly and in a patchy manner following treatment. No significant reinvasion gradients were detected. Aphid population density recovered more rapidly in the reduced rate treatment; with initial evidence for increased densities at the plot centre. Significant patterns of reinvasion were initially detected for both groups of Hymenoptera in the full rate treatment, suggesting that reinvasion of the sprayed area was taking place from untreated surrounding reservoirs. It was concluded that experiments that examine pesticide impacts within small plots will lead to underestimates of effects on dispersive groups including parasitic Hymenoptera.     

Expression of the insecticidal lectin from snowdrop (Galanthus nivalis agglutinin; GNA) in transgenic wheat plants: effects on predation by the grain aphid Sitobion avenae

Transgenic wheat plants containing the gene encoding snowdrop lectin (Galanthus nivalis agglutinin; GNA) under the control of constitutive and phloem-specific promoters were generated through the particle bombardment method. Thirty-two independently derived plants were subjected to molecular and biochemical analyses. Transgene integration varied from one to twelve estimated copies per haploid genome, and levels of GNA expression from 0 to ca. 0.2% of total soluble protein were observed in different transgenic plants. Seven transgenic plants were selected for further study. Progeny plants from these parental transformants were selected for transgene expression, and tested for enhanced resistance to the grain aphid (Sitobion avenae) by exposing the plants to nymphal insects under glasshouse conditions. Bioassay results show that transgenic wheat plants from lines expressing GNA at levels greater than ca. 0.04% of total soluble protein decrease the fecundity, but not the survival, of grain aphids. We propose that transgenic approaches using insecticidal genes such as gna in combination with integrated pest management present promising opportunities for the control of damaging wheat pests.     

小麦抗蚜品种（系）或材料的抗性遗传测定及筛选

测定了部分小麦品种（系）或材料的丁布（ＤＩＭＢＯＡ）含量及几个和抗蚜性有关的物理性状（叶、叶毛长度和密度,蜡质含量）,同时对这些品种（系）或材料进行抗麦长管蚜（Ｍacrosiophum avenae(F.))鉴定,统计其累计蚜量。结果表明,丁布含量及各物理性状与累计蚜量均成负相关关系,通过多目标综合决策分析,认为１粒小麦（Ｔriticum monococcum)和材料９８－１０－９是比较好的抗性种质资源,生产上广泛推广的千斤早是感蚜的品种。     

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.     

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.     

Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.     

Validation of models that predict the peak density of grain aphid (Sitobion avenue) and yield loss in winter wheat

Aphid counts and yield results from a three-year field trial of the effectiveness of insecticides applied at various growth stages of winter wheat, were used to test the accuracy of the predictions of the Entwistle and Dixon (1986, 1987) models for forecasting aphid damage and population growth. In general, the peak aphid populations of Sitobion avenae and damage were not accurately predicted but the spray recommendations, which would have resulted from the predictions, would have been correct in each of the three years; one outbreak and two non-outbreak years. In particular the effectiveness of early spraying was over-estimated because the persistence of the effect of insecticides was over-estimated. It is recommended that further work be done on the rate of development of aphid populations following application of insecticides.     

Development and reproductive potential of the cereal aphid Sitobion avenae on resistant wheat lines (Triticum monococcum)

The effect of wheat resistance in lines of Triticum monococcum L., on the reproductive performances of the cereal aphid (Sitobion avenae F.) was investigated. Aphids were reared from birth to adult moult either on resistant or susceptible wheat lines, and transferred as apterae to both host genotypes. The influence of these transfers on the subsequent adult weight, gonad status and reproductive performances was evaluated. Aphids transferred from resistant to susceptible plants proved able to compensate for their poor nymphal growth, mainly through additional embryo growth and an increase in the number of matured embryos within the first 10 days of their adult life. Most aphids transferred from susceptible to resistant plants died within the first week following the transfer. Their most advanced embryos matured and were born, but subsequent embryo growth was quickly reduced. The reproductive strategies adopted by S. avenae when facing plant resistance, and the hypothesis of a resistant mechanism based on a poor nutritional state of the resistant plants are discussed.     

Effects of DIMBOA on detoxification enzymes of the aphid Rhopalosiphum padi (Homoptera: aphididae)

The presence of glutathione transferases and esterase activity was investigated in Rhopalosiphum padi and the effects of the cereal hydroxamic acid, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) on these detoxification enzymes was studied. Activity of glutathione S-transferases and general esterases was determined for adult aphids feeding on a natural diet lacking DIMBOA and on an artificial DIMBOA-containing diet for 48 hours. In vivo, DIMBOA in the diet inhibited the activities of esterases by 50-75% at all concentrations tested (0.5-4 mM). The activity of glutathione transferase was inhibited to a lesser extent (30%) at the higher concentrations of DIMBOA. In vitro, DIMBOA generally inhibited the activity of esterases with an IC(50) of 33 micro M, and had a slight inhibitory effect on glutathione S-transferases. These effects of DIMBOA could make the aphids vulnerable to electrophilic agents and insecticides which may be metabolized via esterases and GSTs. In cereals, therefore, DIMBOA may act by interfering with esterase- or GST-mediated detoxification of xenobiotics by aphids.     

外源化合物诱导后小麦对麦长管蚜和粘虫的抗虫性研究

喷施外源化合物和昆虫取食均可诱导小麦的防御反应,如挥发物组成发生改变、某些次生物质含量增加或减少,进而影响昆虫和天敌的行为反应。本实验中小麦苗经茉莉酸或几丁质喷施诱导,可显著提高小麦中丁布的含量,但茉莉酸甲酯的诱导作用不明显。喷施茉莉酸及麦长管蚜或粘虫取食诱导小麦,会导致小麦挥发物的种类及含量与对照相比有显著不同,3种处理间小麦的挥发物也存在显著差异。用经茉莉酸处理的麦苗饲养麦长管蚜和粘虫,可显著抑制二者的生长发育速度,使体重减轻,并导致麦长管蚜繁殖力下降。经茉莉酸处理的麦苗的挥发物对粘虫寄生蜂有吸引作用,表明茉莉酸在诱导小麦产生直接抗虫性的同时,还能诱导其释放吸引天敌的挥发性化合物从而产生间接抗性。     

Resistance of cereals to aphids: Interaction between hydroxamic acids and the aphid Sitobion avenae (Homoptera: Aphididae)

The hydroxamic acids in the seedlings of four varieties of winter wheat were extracted initially in boiling methanol in order to avoid enzymatic hydrolysis. The increase in numbers of aphids on these varieties of wheat were recorded. HPLC analysis of hydroxamic acids in the extracts showed the presence of DIMBOA-glucoside, DIMBOA-aglucone and its benzoxazolinone (MBOA). There was a highly significant negative correlation between the concentration of DIMBOA-aglucone in the seedlings and aphid performance. However, the association between aphid performance and DIMBOA-aglucone in the tips of the seedlings was weaker. In general aphid infestation of wheat seedlings slightly increased the concentration of all the hydroxamic acid derivatives. Moreover, aphids ingested hydroxamic acids and were able to detoxify some of the DIMBOA-aglucone they ingested.     

Resistance and susceptibility to colour forms of the aphid Sitobion avenue in spring and winter wheats (Triticum aestivum)

Glasshouse assessments of resistance to S. avenae in 29 entries of wheat and two of rye were made by releasing half-grown aphids on randomised plants at the stem extension phase of growth. Wheat cvs Kador, Amigo, Highbury and Lutescens 1377 were resistant and cvs Sentry and Talavera de Bellevue partially resistant. Cv. Klein Acero, a breeding line TB68/6/10 and Lerma Rojo selections 197 to 200 were highly susceptible to S. avenae although the latter are moderately resistant to greenbug (Schizaphis graminum) (Starks & Merkle, 1977). The rye cultivars were susceptible to 5. avenae and no cultivar was found to be resistant to Metopolophium dirhodum. Clonal stocks of S. avenae, differing in colour, varied in their ability to form large populations on susceptible cultivars, and hence in their differentiation of susceptible from resistant wheat. No clone was detected with specific ability to attack the resistant cvs Kador and Amigo.     

Biochemical basis of winter wheat resistance to the grain aphid, Sitobion avenae

Six winter wheat cultivars with differing degrees of resistance to the grain aphid, Sitobion avenae (F.), were studied under field conditions. Resistance was measured in terms of non-preference and antibiosis on plants at seven growth stages. The varieties Saga and Grana were most resistant in terms of both non-preference and antibiosis to S. avenae at all growth stages examined. The varieties Liwilla and Dana were relatively susceptible to aphid attack. The number of aphids was directly proportional to the total content of free and essential amino acids. The level of resistance showed a similar, but not identical, relationship with the observed concentration of soluble proteins. A higher degree of cultivar resistance was associated with a higher value on a toxicity index, which is the ratio between the free-phenols and free-amino acids content. Obtained results suggest that the resistance of winter wheat cultivars to the grain aphid was based mainly on the mechanism of antibiosis.

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Résumé Six cultivars de blé d'hiver, présentant différents degrés de résistance au puceron des grains, S. avenae, ont été étudiés dans la nature. La résistance a été évaluée en fonction de l'antibiose et de l'absence de préférence de plantes à 7 stades de développement. Les variétés Saga et Grana ont été les plus résistantes, suivant ces deux critères, pour tous les stades de puceron étudiés. Les variétés Liwilla et Dana ont été relativement sensibles. Les effectifs de pucerons étaient proportionnels à la teneur totale en acides aminés libres essentiels. Les concentrations en protéines solubles présentent une relation de même type, mais pas identique, avec le niveau de résistance. Un haut degré de résistance a été associé à une valeur élevée de l'indice de toxicité, rapport entre les phénols libres et la teneur en acides aminés libres. Ces résultats suggèrent une résistance des cultivars de blé d'hiver à S. avenae liée principalement aux mécanismes d'antibiose.

     

Short-term forecasting of peak population density of the grain aphid (Sitobion avenae) on wheat

The trends in population density of Sitobion avenae in wheat fields were analysed for a total of 32 sites over the period 1975 to 1983 in eastern England and the Netherlands. The peak population density on each field was positively correlated with the population densities at the end of ear emergence, mid-anthesis and the end of anthesis. It was also positively correlated with the observed rates of increase of the aphids on the crop immediately before these stages. Both parameters were incorporated in multiple regressions to forecast peak population density, and data from a further nine populations monitored in 1984 was used to validate the model. The accuracy of these forecasts, based on two counts on the crop, increased from ear emergence to the end of anthesis, the forecast at mid-anthesis of peak density being much more accurate than any other published method.     

Effect of light on DIMBOA-glucoside concentration in wheat {Triticum aestivum L.)

DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) glucoside in wheat has been suggested to play a role in plant resistance to cereal aphids. Thus there is considerable interest in trying to breed modern wheat varieties with increased concentrations of this compound. To further such work we assessed the effects of light intensity on DIMBOA glucoside production in wheat seedlings under both indoor and outdoor conditions. Light had a marked effect on DIMBOA-glucoside concentrations, with levels in plants being negatively related to light intensity. Our findings suggest that breeding aimed at increasing levels of DIMBOA-glucoside would be most effective if test plants for selection were to be grown under weak light conditions.     

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.     

Short-term forecasting of wheat yield loss caused by the grain aphid (Sitobion avenae) in summer

A damage model was used to take into account the effect on winter wheat yield of the size, duration and timing of Sitobion avenae infestation in summer, and the influence of insecticide applications. It was validated as far as possible using available data, and appeared to be sufficiently accurate to be useful. The model was applied to a total of 32 winter wheat fields over the period 1975 to 1983 in eastern England and the Netherlands, to obtain estimates of yield losses associated with not applying insecticides at the end of ear emergence (G.S. 59), mid-anthesis (G.S. 65) or the end of anthesis (G.S. 69). These estimates of future yield losses were related in multiple regressions to the number of S. avenae per tiller at the time the insecticide was applied, and the rate of population increase over the previous few days. Basing the decision about whether to apply insecticide on forecasts from the multiple regression equations appeared to be slightly more profitable than prophylactic spraying when the chemical cost alone was considered, but substantially more profitable when the application cost and wheeling loss were also taken into account. The strategy minimising losses involved forecasts at all three crop growth stages. It was validated using a further 21 fields studied in 1984 and 1985, and gave better results than the EPIPRE system, which over-estimated the number of fields requiring spraying, and the economic threshold of George & Gair (1979), which under-estimated the number requiring spraying. However, the accuracy of the damage model needs to be checked against measured yield losses in order to establish the success of the multiple regression strategy conclusively.