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.     

Systemic control efficacy of neonicotinoids seeds dressing on English grain aphid (Hemiptera: Aphididae)

English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is an important pest of wheat (Triticum aestivum L.), and is usually controlled by intensive foliar sprays of pesticides under field conditions. In order to reduce labour costs and increase the utilization of pesticides, neonicotinoids seed treatment was studied as a simple and accurate control technology for S. avenae. We evaluated the mortality of imidacloprid, acetamiprid, thiamethoxam, clothianidin, nitenpyram and dinotefuran to the English grain aphid by seed dressing methods in the laboratory, and found that the toxicity with that LC₅₀ of clothianidin (20.97?a.i.?g/100?kg seeds) and thiamethoxam (28.84?a.i.?g/100?kg seeds) to S. avenae are higher than other neonicotinoids. LC₅₀ values of nitenpyram, imidacloprid and acetamiprid ranged between 120?a.i.?g/100?kg seeds and 210?a.i.?g/100?kg seeds. Dinotefuran showed the lowest toxicity with LC₅₀ value 565.76?a.i.?g/100?kg seeds to English grain aphid. Field plot experiments were conducted to investigate the control efficacy of neonicotinoids seed treatment for the aphid, and the effects on growth of wheat. Field observations indicated that clothianidin and thiamethoxam provided the better control efficacy on the English grain aphid than imidacloprid, and had no influence on wheat seedling emergence. These results showed that seed treatment by neonicotinoids was effective against S. avenae throughout the growth period, furthermore, thiamethoxam and clothianidin were the effective and safe alternative options for S. avenae management in the crop.     

Relationship between Water Soluble Carbohydrate Content,Aphid Endosymbionts and Clonal Performance of Sitobion avenae on Cocksfoot Cultivars

Aphids feed on plant phloem sap, rich in sugars but poor in essential amino acids. However, sugars cause osmotic regulation problems for aphids, which they overcome by hydrolysing the sugars in their gut and polymerising the hydrolysis products into oligosaccharides, excreted with honeydew. Aphids harbour primary bacterial endosymbionts, which supply them with essential amino acids necessary for survival. They also harbour secondary (facultative) endosymbionts (sfS), some of which have a positive impact on life history traits, although it is not yet known whether they also play a role in providing effective tolerance to differing levels of water soluble carbohydrates (WSCs). We investigated the relationship between WSC content of cocksfoot cultivars and performance of clones of the English grain aphid Sitobion avenae F. We evaluated how clone genotype and their sfS modulate performance on these different cultivars. We therefore examined the performance of genetically defined clones of S. avenae, collected from different host plants, harbouring different sfS. The performance was tested on 10 Dactylis glomerata L. cultivars with varying WSC content. D. glomerata is known as a wild host plant for S. avenae and is also commercially planted. We found that high WSCs levels are responsible for the resistance of D. glomerata cultivars to specific S. avenae clones. The minimum level of WSCs conferring resistance to D. glomerata cultivars was 1.7% dw. Cultivars with a WSC content of 2.2% or higher were resistant to S. avenae and did not allow reproduction. Our results further indicate that sfS modulate to some extend host plant cultivar adaptation in S. avenae. This is the first study revealing the importance of WSCs for aphid performance. Cocksfoot cultivars with a high content of WSCs might be therefore considered for aphid control or used for resistance breeding in this and other grass species, including cereals.     

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.     

Insight into watery saliva proteomes of the grain aphid,Sitobion avenae

The grain aphid, Sitobion avenae, is an economically important cereal pest worldwide. Aphid saliva plays an essential role in the interaction between aphids and their host plants. However, limited information is available regarding the proteins found in the saliva of S. avenae. Here, the watery saliva proteins from S. avenae were collected in an artificial diet and identified using a liquid chromatography–mass spectrometry/mass spectrometry analysis. A total of 114 proteins were identified in S. avenae saliva, including several enzymes, binding proteins, and putative effectors, as well as other proteins with unknown functions. In comparison with salivary proteins from nine other aphid species, the most striking feature of the salivary protein from S. avenae was the different patterns of protein functions. Several orthologous proteins secreted by other aphid species such as glucose dehydrogenase, elongation factors, and effector C002 were also detected in S. avenae saliva and speculated to play a significant role in aphid–plant interactions. These results provide further insight into the molecular basis between aphids and cereal plant interactions.     

Bio-fertilizers and micronutrients affect the digestibility,detoxification, and intermediary metabolisms of English grain aphid,Sitobion avenae,in greenhouse

The English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is one of the most serious pests of cereals as the transmitter of viral diseases, mainly in wheat, Triticum aestivum. This agricultural pest is controlled with chemical insecticides, which is environmental pollutants and toxic for human. This study evaluated the potential of alternative environmentally friendly compounds to control this insect pest. The activities of digestive, antioxidants, and intermediary metabolism enzymes of S. avenae reared on wheat plants treated with bio-fertilizers (Biofarm and Probio96) and micronutrients (Librel Zinc and α-Iron) in the greenhouse were evaluated. The results reveal that α-amylase, total protease, trypsin, chymotrypsin, amino- and carboxypeptidases, alanine- and aspartate- aminotransferases, and acid phosphatase enzymes had lower activities in S. avenae reared on Biofarm treated plants compared to control. On the other hand, aphids reared on treated plants with Biofarm had the highest activities of antioxidant enzymes superoxide dismutase, catalase, peroxidase, and ascorbate oxidase, γ- glutamyl transferase, as well as lactate dehydrogenase. Moreover, the oxidized/reduced thiols ratio and malondialdehyde indicated higher activity in the aphids reared on Biofarm-treated plants than control. These results suggest that the bio-fertilizer Biofarm may compromise the physiology of S. avenae as a potential alternative toll in the integrated pest management of this aphid.     

Effect of light intensity on colour morph formation and performance of the grain aphid Sitobion avenae F. (Homoptera: Aphididae)

The grain aphid Sitobion avenae F., one of the major pest aphids of cereals in Central Europe, exhibits colour polymorphism, even within the same clones. Although there is evidence that green and brown morphs of S. avenae contain different carotenoids, the mechanisms determining the induction of colour morphs are unknown. The common understanding is that the formation of colour morphs is controlled by light and affected by genetic and environmental factors and by host plant species. So far, there is no unequivocal evidence that light intensity, photoperiod, or a mixture of several variables are involved in the induction of S. avenae colour formation, resulting in the induction of S. avenae colour formation and carotenoid synthesis.Here we determined the effect of light intensity on the colour formation and performance of ten clones of S. avenae with experiments that controlled for the effects of host plant and genetic factors. We found that some clones remained green under all test conditions. In other clones, colour morph formation was controlled by light. The synthesis of carotenoids correlated with changes in colour formation. Host plant did not affect colour formation in the ten clones studied. Although colour of the aphid clones did not affect their performance, high light intensity increased the fecundity and fresh weight of S. avenae clones, while low light intensity stimulated the production of alatae.     

Effect of three isolates of Pandora neoaphidis from a single population of Sitobion avenae on mortality,speed of kill and fecundity of S. avenae and Rhopalosiphum padi at different temperatures

We studied the effect of three Pandora neoaphidis isolates from one Sitobion avenae population, three temperatures, and two aphid species namely S. avenae and Rhopalosiphum padi on (i) aphid mortality, (ii) time needed to kill aphids, and (iii) aphid average daily and lifetime fecundity. A total of 38% of S. avenae and 7% of R. padi died and supported fungus sporulation. S. avenae was killed 30% faster than R. padi. Average daily fecundity was negatively affected only in S. avenae inoculated with, but not killed by, P. neoaphidis. Nevertheless, lifetime fecundity of both aphid species inoculated and sporulating with P. neoaphidis was halved compared to lifetime fecundity of surviving aphids in the control. Increased temperature resulted in higher mortality rates but did not consistently affect lethal time or fecundity. Results suggest that (i) temperature effects on virulence differ between isolates, even when obtained within the same host population, and (ii) even though an isolate does not kill a host it may reduce its fecundity. Our findings are important for the understanding of P. neoaphidis epizootiology and for use in pest-natural enemy modelling.     

Preference of cereal aphids for different varieties of winter wheat

This paper reports on the development of a simple and robust preference meter (developed in-house) to score the host choice behavior of apterous aphids. With this tool, the preferences of two important cereal aphids Sitobion avenae (Fab.) and Metopolophium dirhodum (Walker) were investigated against four different varieties of winter wheat (Triticum aestivum L.) with a different susceptibility for Fusarium head blight (FHB). Differences in the choice behavior of both aphid species were observed for different wheat varieties. The preferred wheat variety of S. avenae and M. dirhodum was not the same. Also, both aphid species clearly had a differential preference for seedlings and ears. Using seedlings, M. dirhodum was about 1.8 times more rapid in making its choice than S. avenae. In separate experiments with ears, S. avenae was 4.5 times faster than in the experiments with seedlings. In the present study, we aim to highlight differences in preference behavior in relation to potential mechanisms for host selection.     

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.     

Horizontal transfer of facultative endosymbionts is limited by host relatedness

Heritable microbial symbionts can have important effects on many aspects of their hosts’ biology. Acquisition of a novel symbiont strain can provide fitness benefits to the host, with significant ecological and evolutionary consequences. We measured barriers to horizontal transmission by artificially transferring facultative symbionts from the grain aphid, Sitobion avenae, and five other aphid species into two clonal genotypes of S. avenae. We found the symbiont Hamiltonella defensa establishes infections more easily following a transfer from the same host species and that such infections are more stable. Infection success was also higher when the introduced symbiont strain was more closely related to the strain that was originally present in the host (but which had previously been removed). There were no differences among successfully established symbiont strains in their effect on aphid fecundity. Hamiltonella defensa did not confer protection against parasitoids in our S. avenae clones, although it often does in other aphid hosts. However, strains of the symbiont Regiella insecticola originating from two host species protected grain aphids against the pathogenic fungus Pandora neoaphidis. This study helps describe the extent to which facultative symbionts can act as a pool of adaptations that can be sampled by their eukaryote hosts.     

Entomotoxic action of jackbean lectin (Con A) in bird cherry-oat aphid through the effect on insect enzymes

The mechanism of the toxicity of plant lectins is not clearly understood. The insecticidal activity of plant lectins results from effects on insect metabolism by interfering with gut enzymatic function. Thus, a greater understanding of the mechanisms of plant lectin toxicity in insects is required. This study reports the effects of dietary ingestion of the glucose-mannose binding lectin Concanavaline A (Con A) on bird cherry-oat aphid (Rhopalosiphum padi L.) enzymes involved in protein digestion [aminopeptidase N and cathepsin L (CatL)], sugar (α- and β-glucosidases), and phosphorus (alkaline and acid phosphatase) metabolism. An aphid bioassay test using artificial diets containing Con A is also presented. An increase in the concentration of Con A generally suppressed the activity of glucosidases and phosphatases, and increased the activity of CatL in apterae morphs. Bird cherry-oat aphid performance was affected by the presence of Con A in artificial diets. The lectin added to the liquid diet increased the pre-reproductive period, mortality, and the average time of generation development (T) and decreased fecundity and the intrinsic rate of natural increase (r_m). Aphicidal activity of Con A might be linked to its interference in the activity of digestive enzymes.     

Suitability of three aphid species for Aphidius gifuensis (Hymenoptera: Braconidae): Parasitoid performance varies with hosts of origin

Oviposition behavior and offspring fitness of the parasitoid Aphidius gifuensis (Ashmead) were compared on three aphid species, Sitobion avenae F., Myzus persicae (Sulzer), and Aphis gossypii Glover using wasps collected from both S. avenae and M. persicae. A. gifuensis produced more mummies and adults on S. avenae and M. persicae than on A. gossypii regardless of the host of origin. Mummy production was influenced by attack rate and percentage of aphids superparasitized. The F₁ generations from S. avenae and M. persicae were more female-biased and wasps were larger than those from A. gossypii. Although there were significant differences in development time of A. gifuensis in the three aphid species, the difference was generally shorter than one day. Fewer mummies were produced when A. gifuensis was transferred between S. avenae and M. persicae, but no significant difference was observed in emergence rate, percentage of female offspring, or body size. The effects of host species on A. gifuensis female performance and offspring fitness are discussed, along with the potential for using A. gifuensis to control M. persicae and A. gossypii.     

Effect of the mycotoxin deoxynivalenol on grain aphid <Emphasis Type="Italic">Sitobion avenae</Emphasis> and its parasitic wasp <Emphasis Type="Italic">Aphidius ervi</Emphasis> through food chain contamination

We investigated the influence of the Fusarium mycotoxin deoxynivalenol on the English grain aphid Sitobion avenae (Hemiptera: Aphididae) and its parasitic wasp Aphidius ervi (Hymenoptera: Braconidae) using in vitro laboratory experiments. In this tritrophic interaction, deoxynivalenol caused lethal (declined survival) and sublethal (prolonged nymphal development and reduced reproduction) effects on S. avenae aphids and consequentially led to a decreased production of parasitoid offspring resulting from parasitized deoxynivalenol-contaminated aphids. This paper highlights that the presence of mycotoxins should be considered in environmental risk assessment tests because they may alter the efficiency of biological control agents such as parasitoids through food chain contamination.     

Tripartite Interactions of Barley Yellow Dwarf Virus,Sitobion avenae and Wheat Varieties

The tripartite interactions in a pathosystem involving wheat (Triticum aestivum L.), the Barley yellow dwarf virus (BYDV), and the BYDV vector aphid Sitobion avenae were studied under field conditions to determine the impact of these interactions on aphid populations, virus pathology and grain yield. Wheat varietal resistance to BYDV and aphids varied among the three wheat varieties studied over two consecutive years. The results demonstrated that (1) aphid peak number (APN) in the aphid + BYDV (viruliferous aphid) treatment was greater and occurred earlier than that in the non-viruliferous aphid treatment. The APN and the area under the curve of population dynamics (AUC) on a S. avenae-resistant variety 98-10-30 was significantly lower than on two aphid-susceptible varieties Tam200(13)G and Xiaoyan6. (2) The production of alatae (PA) was greater on the variety 98-10-30 than on the other varieties, and PA was greater in the aphid + BYDV treatment on 98-10-30 than in the non-viruliferous aphid treatment, but this trend was reversed on Tam200(13)G and Xiaoyan6. (3) The BYDV disease incidence (DIC) on the variety 98-10-30 was greater than that on the other two varieties in 2012, and the disease index (DID) on Tam200(13)G was lower than on the other varieties in the aphid + BYDV and BYDV treatments in 2012, but not in 2011 when aphid vector numbers were generally lower. (4) Yield loss in the aphid + BYDV treatment tended to be greater than that in the aphid or BYDV alone treatments across varieties and years. We suggested that aphid population development and BYDV transmission tend to promote each other under field conditions. The aphids + BYDV treatment caused greater yield reductions than non-viruliferous aphids or virus treatment. Wheat varietal resistance in 98-10-30 affects the aphid dispersal, virus transmission and wheat yield loss though inhibits aphid populations from increasing.     

Resistance to multiple cereal aphids in wheat–alien substitution and translocation lines

Rhopalosiphum padi, Schizaphis graminum, and Sitobion avenae are three of the most destructive aphid species of wheat (Triticum aestivum L.). They can significantly reduce wheat yields directly by feeding and indirectly by transmitting viruses. This study aimed to search for resistance to these aphid species among lines derived from different rye (Secale cereale) origins and from Aegilops speltoides, all in the genetic background of the wheat cultivar Pavon F76. Resistance was quantified as aphid weight (R. padi, S. avenae, and S. graminum) and the number of aphids and percentage of infested leaf area exhibiting chlorosis (S. graminum). The most resistant genotypes reduced R. padi and S. avenae weight by 24.2 and 34.3 %, respectively, at the seedling stage, compared with Pavon F76 control plants. Strong S. graminum resistance was found only in A. speltoides-derived lines, the most resistant of which (7A.7S-L5) sustained just 3 % chlorosis and reduced S. graminum colony weight by 67.7 %. One line carrying the 1AL.1RS_am wheat–rye translocation from Amigo wheat (originally from Insave rye) reduced S. avenae weight by 23.2 and 21.8 % in seedling and adult plants, respectively. Single genotypes carrying the complete 1R chromosome or the 1RS chromosome arm derived from E12165 wheat and Presto triticale proved to be resistant to both R. padi and S. avenae at the seedling stage. Further research should be conducted to unravel the genetic basis of resistance to these aphids in 1RS genotypes. The sources of resistance identified here may be useful for incorporating multiple aphid species resistance in wheat breeding programs, particularly for R. padi and S. avenae, to which no resistant wheats have been bred.     

Consumption by carabid beetles of three cereal aphid species relative to other prey types

The cereal aphidRhopalosiphum padi has previously been found to be a low quality prey for a range of generalist arthropod predators. The aim of this study was to reveal, using food consumption experiments whether this applies to other cereal aphids. The question of whether predator feeding capacity increased when several aphid species were offered relative to a single aphid species was also addressed by measuring food consumption on a mixed aphid diet relative to single aphid diets. Food consumption by five carabid beetles of the three cereal aphid speciesRhopalosiphum padi, Sitobion avenae andMetopolophium dirhodum was determined relative to fruit fliesDrosophila melanogaster and the collembolanIsotoma anglicana. Feeding rate was measured as food consumption over 24 hour both for previously satiated and beetles starved for 7 days. Generally the largest aphid consumption was ofM. dirhodum and the lowest ofR. padi, withS. avenae in between. The mixed aphid consumption experiments did not reveal a higher feeding rate on mixed aphid diets relative to single aphid diets. The results indicate low preference forR. padi andS. avenae.     

Functional divergence of three glutathione transferases in two biotypes of the English grain aphid,Sitobion avenae

The English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is a significant pest of cereal crops, but molecular factors and mechanisms that underpin its ability to develop differential biotypes on variable host plants are still not well understood. In this study, we investigated the interactions between two plant secondary metabolites (i.e., gramine and gallic acid) and three glutathione S-transferases (GSTs) of S. avenae. Using artificial diets complemented or not with one of these two plant compounds, we found that gramine had relatively stronger negative effects on fitness of S. avenae biotype 3 (adapted to barley), and gallic acid on that of biotype 4 (adapted to wheat). Gramine significantly induced overexpression of SaveGST1 and SaveGST2 in biotype 4, but not in biotype 3. Gramine also reduced SaveGST3 expression in biotype 4, but not in biotype 3, suggesting biotype-specific effect of GSTs’ regulation. In the treatments with gallic acid, the overexpression of SaveGST1, but not SaveGST2 or SaveGST3, was significantly induced in both biotypes, suggesting a critical role of SaveGST1 in detoxification of phenolic compounds such as gallic acid. The total constitutive GST activity was much higher in biotype 4 than in biotype 3. Significant increase in GST activity was obtained by the addition of both secondary metabolites in biotype 4, but not in biotype 3, showing significantly higher expression plasticity of GSTs in biotype 4. Thus, both constitutive and induced expression of GSTs could affect the adaptability of S. avenae on plants with variable secondary compounds, and thus contribute to the divergence of biotypes in this aphid species.     

Performance of clones and morphs of two cereal aphids on wheat plants with high and low nitrogen content

The great variability of the aphid life cycle and their tendency for host alternation gives rise to aphid clones and morphs. Inter‐ and intraclonal variability may be observed in the responses of aphids to various environmental factors. In this study we aimed to evaluate the influence of intrinsic factors (clone and morph type) on the intrinsic rate of increase (r_m) of the English grain aphid, Sitobion avenae (Fabricius), and the bird cherry‐oat aphid, Rhopalosiphum padi (Linnaeus). For each species four apterous clones were collected from established laboratory colonies and compared to assess their relative fitness on high‐ and low‐nitrogen wheat plants under laboratory conditions. The clones had significantly different intrinsic rates of increase on high‐ and low‐nitrogen plants. All R. padi clones had a higher intrinsic rate of increase and mean relative growth rate than S. avenae. Experiments were also conducted to compare the mean fecundity of apterous and alate morphs of S. avenae and R. padi clones on high‐ and low‐nitrogen wheat plants. On high‐nitrogen plants the apterous morphs of S. avenae clones had significantly higher mean fecundity than alate morphs. There were no significant differences between the mean fecundity of alate morphs of the same species on high‐ and low‐nitrogen plants. The results support the idea of better fitness of specific clones/morphs on certain host plants due to higher and lower intrinsic rates of increase.