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.     

Toxic and deterrent effects of phytohemagglutinin on the grain aphid Sitobion avenae

The toxicity and deterrent effects of phytoheamagglutinin (Phaseolus vulgaris agglutinin, PHA) to the grain aphid (Sitobion avenae F.) was investigated in the laboratory by use of liquid diets or gels containing various PHA concentrations. The addition of PHA to the liquid diet increased the aphid pre-reproductive period, mortality, and generation time and decreased aphid fecundity and intrinsic rate of natural increase. Aphids fed on sucrose-agarose gels with higher concentrations of PHA exhibited no phloem-feeding behavior. The number of gel penetrations was reduced and duration of the pathway phase was increased as PHA concentration increased. These results indicate that PHA is detrimental to S. avenae and that the effect of PHA is at least partially explained by suppression of feeding behaviour. PHA could be useful for managing S. avenae.     

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.     

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 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.     

Cold hardiness and overwintering of the grain aphid Sitobion avenae

ABSTRACT.

• 1 Cold hardiness as measured by supercooling ability in the active stages of the grain aphid Sitobion avenae (F.) decreased progressively with maturation.
• 2 Aphids showed no acclimation response when maintained at low temperatures.
• 3 Starvation did not improve supercooling ability.
• 4 In a single exposure, surface moisture caused inoculation above the inherent supercooling point in a small proportion of a population.
• 5 Field populations show a seasonal change in supercooling ability, which is at a maximum in summer and a minimum in late winter.
• 6 It is concluded that the act of feeding on healthy plant tissue may confer extensive supercooling ability.

     

Antimetabolic effect of phytohemagglutinin to the grain aphid Sitobion avenae fabricius

The insecticidal activity of plant lectins against a wide range of insect species have been intensively studied. Understanding the mechanism of the toxicity of lectins is one of the studied aspects. In the present research, the first step was determine the effect of phytohemagglutinin (PHA) on the development, fecundity and mortality of grain aphid. Next, the effect of PHA lectin on the activity of such enzymes as: α- and β-glucosidases, alkaline (AkP) and acid (AcP) phosphatases, aminopeptidase N and cathepsin L involved in the metabolism of sugar, phosphorus and proteins of an adult apterae aphids was investigated. The PHA lectin added into the liquid diet increased the pre-reproductive period, mortality of Sitobion avenae, the time of generation development and decreased its fecundity and the intrinsic rate of natural increase. In addition, activity of α-glucosidase, alkaline phosphatase and aminopeptidase N of adult apterae exposed to PHA were reduced. The results indicate that the insecticidal activity of PHA on S. avenae may involve changes in activity of the enzymes in the midgut and it may be part of its toxicity.     

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.     

四种类型杀虫剂对麦长管蚜的温度效应及其与主要解毒酶的关系

为了明确杀虫剂毒力受温度的影响及其程度,本文测定了4大类8种药剂在10～25℃下对麦长管蚜的毒力;并测定了麦长管蚜Sitobion avenae(Fabricius)在不同温度下2个解毒酶和1个靶标酶的活性差异。结果表明,高效氯氰菊酯对麦长管蚜表现不规则负温度系数,啶虫脒表现不规则正温度系数,高效氟氯氰菊酯对麦长管蚜的毒力不受温度影响,其他药剂(辛硫磷、毒死蜱、灭多威、丁硫克百威、吡虫啉)均表现为明显的正温度系数效应,以有机磷类杀虫剂表现最为明显,毒死蜱温度系数高达57.70。酶活性实验表明:麦长管蚜在高温下GST活性增强,羧酸酯酶和乙酰胆碱酯酶活性降低。它们的变化规律表明:GST活性与负温度系数密切相关,正温度系数与羧酸酯酶活性和靶标酶乙酰胆碱酯酶活性有关。     

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.     

The diversity and fitness effects of infection with facultative endosymbionts in the grain aphid, Sitobion avenae

Mutualisms with facultative, non-essential heritable microorganisms influence the biology of many insects, and they can have major effects on insect host fitness in certain situations. One of the best-known examples is found in aphids where the facultative endosymbiotic bacterium Hamiltonella defensa confers protection against hymenopterous parasitoids. This symbiont is widely distributed in aphids and related insects, yet its defensive properties have only been tested in two aphid species. In a wild population of the grain aphid, Sitobion avenae, we identified several distinct strains of endosymbiotic bacteria, including Hamiltonella. The symbiont had no consistent effect on grain aphid fecundity, though we did find a significant interaction between aphid genotype by symbiont status. In contrast to findings in other aphid species, Hamiltonella did not reduce aphid susceptibility to two species of parasitoids (Aphidius ervi and Ephedrus plagiator), nor did it affect the fitness of wasps that successfully completed development. Despite this, experienced females of both parasitoid species preferentially oviposited into uninfected hosts when given a choice between genetically identical individuals with or without Hamiltonella. Thus, although Hamiltonella does not always increase resistance to parasitism, it may reduce the risk of parasitism in its aphid hosts by making them less attractive to searching parasitoids.     

The major carotenoid pigments of the grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae)

The economically important grain aphid, Sitobion avenae (F.) shows colour polymorphism, with brown and green forms predominating. Colour is determined both genetically and in response to environmental factors, including nutrition. The biological significance of the colour polymorphism is unknown, although seasonal changes occur in the frequency of colour morphs in the field, whilst the brown morph may have adaptive significance in terms of hymenopterous endoparasitism. The ground colour of aphids is produced by haemolymph pigments, aphins (glucosides) and carotenoids. The latter may be under the synthetic control of intracellular endosymbiotic bacteria. In this study, the major carotenoid pigments of a brown and a green clone of S. avenae were examined using thin layer chromatography (TLC) and high-performance liquid chromatography (HPLC), and their absorbance spectra recorded. Using TLC, the brown clone produced five bands of different R_f, ranging from yellow, to orange-pink to pink in colour. In contrast, the green clone gave only a single yellow band of higher R_f than any of the bands of brown aphids. Following separation of carotenoids by HPLC, brown aphids gave seven peaks and green aphids five. Comparison of absorbance maxima with known published values for carotenoids provides strong evidence for the identification of four of the carotenoid pigments from brown aphids (RB-4, 3,4-didehydrolycopene; RB-5, torulene; RB-6; lycopene; RB-7, γ-carotene) and one from green aphids (RG-2, α-carotene). The other carotenoids remain unidentified. The biosynthesis and possible biological relevance of the various pigments of S. avenae are briefly discussed.     

Impact of intercropping aphid-resistant wheat cultivars withoilseed rape on wheat aphid (Sitobion avenae) and its natural enemies

The effects of intercropping of wheat cultivars and oilseed rape on the densities of wheat aphid, Sitobion avenae, and their arthropod natural enemies were evaluated. Three winter wheat cultivars with different resistant levels to S. avenae were used: ‘KOK’ (high resistance), ‘Xiaobaidongmai’ (low resistance) and ‘Hongmanghong’ (susceptible). The results showed that the densities of S. avenae were significantly higher on the monoculture pattern than on either the 8-2 intercropping pattern (eight rows of wheat with two rows of oilseed rape) or the 8-4 intercropping pattern (eight rows of wheat with four rows of oilseed rape). The mean number of predators and the mummy rates of S. avenae were significantly higher in two intercropping patterns than those in the monoculture pattern. The densities of S. avenae, ladybeetles, and mummy rate of S. avenae were significantly different among different wheat cultivars. The highest densities of S. avenae and ladybeetles were found on wheat cultivar Hongmanghong. The lowest densities of S. avenae associated with high mummy rate of S. avenae were found on wheat cultivar Xiaobaidongmai. The results showed that wheat-oilseed rape intercropping conserved more predators and parasitoids than in wheat monoculture fields, and partial resistance of wheat cultivar Xiaobaidongmai had complementary or even synergistic effects on parasitoid of S. avenae.     

Molecular interactions between wheat and cereal aphid (Sitobion avenae): analysis of changes to the wheat proteome

Aphids are major insect pests of cereal crops, acting as virus vectors as well as causing direct damage. The responses of wheat to infestation by cereal aphid (Sitobion avenae) were investigated in a proteomic analysis. Approximately, 500 protein spots were reproducibly detected in the extracts from leaves of wheat seedlings after extraction and 2‐DE. Sixty‐seven spots differed significantly between control and infested plants following 24 h of aphid feeding, with 27 and 11 up‐regulated, and 8 and 21 down‐regulated, in local or systemic tissues, respectively. After 8 days, 80 protein spots differed significantly between control and aphid treatments with 13 and 18 up‐regulated and 27 and 22 down‐regulated in local or systemic tissues, respectively. As positive controls, plants were treated with salicylic acid or methyl jasmonate; 81 and 37 differentially expressed protein spots, respectively, were identified for these treatments. Approximately, 50% of differentially expressed protein spots were identified by PMF, revealing that the majority of proteins altered by aphid infestation were involved in metabolic processes and photosynthesis. Other proteins identified were involved in signal transduction, stress and defence, antioxidant activity, regulatory processes, and hormone responses. Responses to aphid attack at the proteome level were broadly similar to basal non‐specific defence and stress responses in wheat, with evidence of down‐regulation of insect‐specific defence mechanisms, in agreement with the observed lack of aphid resistance in commercial wheat lines.     

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 extreme,fluctuating temperature events on life history traits of the grain aphid,Sitobion avenae

Altered temperatures affect insects’ life history traits, such as development period and fecundity, which ultimately determine population growth rates. Understanding insects’ thermal biology is therefore integral to population forecasting and pest management decision‐making such as when to utilise crop spraying or biological control. Aphids are important crop pests in temperate regions, causing considerable yield losses. The aphid thermal‐biology literature is, however, heavily biased towards the effects of rising mean temperatures, whereas the effects of fluctuating, extreme climatic events (e.g., heat waves and sub‐zero cold periods) are largely overlooked. This study assessed the effects of laboratory‐simulated heat waves and sub‐zero cold periods on the survival, development period, and fecundity of the grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae: Microsiphini), in addition to assessing maternal effects on the birth weight and development period of the offspring of exposed individuals. Exposure to heat stress periods (total of 16 h at 30 °C) significantly reduced aphid fecundity and increased physiological development period (in day‐degrees) resulting in a reduced population growth rate. Cold exposure (total of 1.33 h at ?15 °C) reduced population growth rate due to an elongated development period (in days), but did not affect fecundity or physiological development period (in day‐degrees). Both cold and heat stress significantly reduced aphid survival. Maternal experience of heat stress reduced nymphal birth weight although nymphal development period was not affected by either cold or heat stress. The results suggest that including the effects of fluctuating, extreme temperature events on aphid life history in population forecast models is likely to be of great importance to pest management decision‐making. The demonstration of maternal effects on birth weight also suggests that cross‐generational effects of heat waves on population growth rates could occur.     

Effects of hydroxamic acids on the resistance of wheat to the aphid Sitobion avenae

Resistance to the aphid Sitobion avenae F. was assessed on six wheat cultivars of known concentrations of total hydroxamic acids. A range of values for intrinsic rate of increase (r_m) were obtained, 96% of the variation in which was explained by acid concentrations. Of the components of r_m, age-specific fecundity was the most significant factor contributing to resistance.     

Mobility of apterous grain aphids Sitobion avenae within wheat fields

In a field study of the grain aphid Sitobion avenae (F.) almost all apterous aphids were found to move from the natal ear before reproducing, and alatiform nymphs usually moved between ears during their development. Apterae were very mobile, with over 50% staying on one ear for less than 24 h. Movements did not appear to be a response to climatic conditions, predation or colony density.

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Résumé Lors de l'étude de Sitobion avenae dans la nature, on a constaté que presque tous les individus aptères avaient quitté leur épi d'origine avant la reproduction, et que les larves de type ailé s'étaient déplacées généralement entre les épis pendant leur développement. Les aptères étaient très mobiles, la majorité restant moins de 24 h sur le même épi. Ces déplacements n'ont pas semblé dépendre des conditions climatiques, de la prédation ou de la densité des colonies.