Induced proteolysis within the bird cherry leaves evoked by Rhopalosiphum padi L. (Hemiptera, Aphidoidea)

The objectives of this study were to elucidate the impact of bird cherry-oat aphid (Rhopalosiphum padi L.) feeding on functioning of the proteolytic machinery in bird cherry leaves. Biochemical analyses proved that R. padi feeding in tissues of primary host stimulated activity of the two major fractions of proteinases (extracted at the optimal pH values: 5.0 and 7.0). Additionally, it has been demonstrated that aphids' feeding on bird cherry led to a decline in levels of albumins and globulins (main protein fractions in P. padus leaves). The opposite tendency, regarding the amounts of these protein fractions was ascertained at the phase of disappearance of R. padi population on tested shoots. Furthermore, it is reported that an increase in activity of the analysed enzymes and a decline in the content of tested protein fractions, were proportional to density of aphid individuals developing on P. padus side shoots. It is hypothesized that long-term R. padi feeding may lead to intensifying the catabolic processing of proteins by the activated proteolytic machinery in bird cherry leaves. The multi-level biological functions of endogenous plant proteinases and their significance in triggering the defense reactions in aphid-infested plant tissues are discussed.     

Host choice and host leaving in Rhopalosiphum padi (Hemiptera: aphididae) emigrants and repellency of aphid colonies on the winter host

Host choice and winter-host leaving in emigrants of bird cherry-oat aphid, Rhopalosiphum padi (Linnaeus), were investigated in the laboratory. In settling choice tests, emigrants collected from the winter host, Prunus padus, preferred this plant over a summer host, oats. Emigrants which had left P. padus for up to 24 h did not express a preference as a group, and those which had left for 24-48 h preferred oats. Eighty seven percent of emigrants caged as fourth-instar nymphs on P. padus leaves abandoned the host by the second day of adult life, and apparently did not subsequently return to the leaf. In an olfactometer, P. padus leaves which had supported spring generations of R. padi were repellent to emigrants. Volatiles were entrained from uninfested and R. padi-infested P. padus using cut twigs in the laboratory as well as intact twigs on a tree in the field. Entrainment extracts from uninfested P. padus had no effect on emigrants in the olfactometer, whereas those from twigs infested with nymphal emigrants were repellent. The study indicates that in R. padi, host-alternation is driven by behavioural changes which occur in individuals as well as between morphs.     

Probing behavior of bird cherry-oat aphid Rhopalosiphum padi (L.) on native bird cherry Prunus padus L. and alien invasive black cherry Prunus serotina Erhr. in Europe and the role of cyanogenic glycosides

The probing behavior of bird cherry-oat aphid Rhopalosiphum padi was studied on its natural winter host in Europe, the bird cherry Prunus padus, and on the invasive black cherry Prunus serotina, on which spring generations of R. padi do not survive. The EPG-recorded behavior of R. padi on bird cherry and black cherry showed differences in crucial aspects of probing and feeding. The period of the pre-phloem penetration was twice as long and rarely interrupted in aphids on bird cherry as opposed to aphids on black cherry. On black cherry, there was a considerable delay between finding and accepting the phloem. Aphids that had sampled phloem sap either refused to ingest it or the ingestion periods were very short. Amygdalin and prunasin (cyanogenic glycosides present in leaves of Prunus) seriously impeded ingestion activities when applied in pure sucrose diet. The role of amygdalin and prunasin in winter host plant selection and host alternation in R. padi is discussed.     

Growth, survival and reproduction of the bird-cherry aphid, Rhopalosiphum padi, on its primary host

Fundatrices died when caged on senescent leaves of bird cherry on which oviparae thrived. Fundatrigeniae had more ovarioles and a higher reproductive rate than fundatrices. Oviparae developed and matured eggs on unfurling leaves but they took longer to reach maturity and grew more slowly than when reared on senescent leaves. Fundatrices and oviparae in addition to having an intrinsic preference for bird cherry over other plants did better on particular growth stages of their primary host.     

Host acceptance by aphids: probing and larviposition behaviour of the bird cherry-oat aphid, Rhopalosiphum padi on host and non-host plants

The probing and larviposition behaviour of the bird cherry-oat aphid, Rhopalosiphum padi on summer and winter host plants were investigated using electrical penetration graph (EPG) coupled with simultaneous video recording. In this way the precise probing history prior to parturition can be monitored and the location of possible reproductive stimulants identified. On the host plant, all gynoparae (autumn winged females that give birth to sexual females on bird cherry, Prunus padus, the primary host) and 55% of winged virginoparae (summer females which produce further virginoparae on barley, Hordeum vulgare, a secondary host) initiated larviposition before phloem contact. However, 90% of wingless virginoparae (on barley) contacted the phloem before first larviposition whilst 10% did not. Thus, phloem contact does not appear to be a pre-requisite for these aphid forms to initiate reproduction.     

Ovariole number and fecundity for the two emigrating generations of the bird cherry-oat aphid (Rhopalosiphum padi) in Sweden

Abstract. 1. The number of ovarioles and the potential fecundity in first (fundatrigenia) and second generation emigrants of Rhopalosiphum padi (L.) was investigated.
2. The relationships between weight and host quality on ovariole number were investigated.
3. The first generation of emigrants had a greater number of ovarioles and a higher fecundity than the second.
4. There was a positive relationship between ovariole number and weight.
5. The number of ovarioles and weight decreased with decreasing host quality.
6. The results do not agree with a recently proposed reproductive strategy of aphids where the number of ovarioles are supposed to be independent of weight and host quality.
7. In years with a high initial population on bird cherry, the migration to grasses, e.g. cereals, will be earlier, probably larger and, to a greater extent, consists of aphids which have a higher reproductive rate than in years with a small initial number on bird cherry.     

Nutritional enhancement of host plants by aphids - a comparison of three aphid species on grasses

Three aphid species were compared with respect to ability of enhancing the nutritional quality of their host plants. Rhopalosiphum padi, which does not induce macroscopic changes in its host plants, was compared with Schizaphis graminum and Diuraphis noxia, both of which induce distinctive types of chlorotic lesions. Phloem sap samples were collected from severed stylets of feeding aphids and from exudates of cut leaves of plants uninfested or infested with each aphid species. Samples were analyzed for concentrations of individual amino acids.Compared to R. padi, S. graminum ingested phloem sap with a two-fold higher concentration of amino acids and a much higher proportion of essential amino acids. Similar differences between these two aphid species were observed on both wheat and barley. For each aphid species, the absolute concentrations of amino acids and the relative proportions of essential amino acids were similar between the two host plants. Effects of D. noxia were similar to those of S. graminum, though less dramatic. Exudates from leaves infested with each aphid species showed relative concentrations of individual amino acids that were similar to those in the corresponding stylet exudates. Based on comparison of stylet exudates and cut leaf exudates from infested and uninfested plants, R. padi seems to have little effect on amino acid composition of phloem. Changes in the phloem induced by both S. graminum and D. noxia appear to be systemic, affecting at least the whole leaf they are feeding on. The changes observed for D. noxia and for S. graminum are likely to be nutritionally advantageous for the aphids and are expected to affect the aphids' dependence on nutritional supplementation by intracellular symbionts (Buchnera).     

Feeding substrates and behaviors of Western cherry fruit fly (Diptera: Tephritidae)

A study was conducted to determine the abundance of potential foods and the feeding substrates and behaviors of the western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), in 2005, 2006, and 2007 in central Washington state. Aphid colonies with honeydew, a presumed food source for flies, were not seen on randomly selected branches of sweet cherry trees, Prunus avium L., but leaves with cherry juice, fruit that were damaged, and leaves with bird feces were commonly seen, especially later in the season. Grazing, a behavior in which the mouthparts rapidly move up and down and touch plant surfaces without discrete substances visible to the human eye, was seen more frequently in flies on leaves than on fruit. Grazing occurred more frequently than feeding on extrafloral nectaries (EFNs) on leaf petioles, cherry juice on leaves, and bird feces on leaves. The percentages of females and males that grazed on leaves were not different in 2 of 3 yr, but the percentage of females that grazed was higher in a third year. Percentages of female and male flies that fed on EFNs, cherry juice, and bird feces did not differ. More flies grazed the tops than bottoms of leaves. Flies also grazed on leaves of apple, pear, and grape. The results support the hypotheses that R. indifferens feeds mostly on leaves rather than fruit and that leaf surfaces may be the main feeding substrates for R. indifferens throughout the season.     

Effect of a co-occurring aphid on the susceptibility of the Russian wheat aphid to lacewing predators

Previous field experiments indicated that the presence of the bird cherry-oat aphid, Rhopalosiphum padi (L.), on perennial grasses can decrease the effectiveness of predatory lacewings, Chrysoperla plorabunda (Fitch), in reducing populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko). We tested the hypothesis that R. padi deflects predation away from D. noxia because it feeds in sites that are more accessible to predators. We quantified the behavior of lacewing larvae on crested wheatgrass plants bearing either D. noxia alone or an equal mixture of D. noxia and R. padi. On non-flowering plants, R. padi typically occurred on leaf sheaths or open blades, and was encountered and captured more often than D. noxia, which usually fed within immature, rolled leaves. Overall time-budgets of lacewings did not differ between the pure-D. noxia and mixed-species treatments, but >75% of the time spent consuming aphids in the mixed-species treatment was devoted to R. padi. On flowering plants, D. noxia usually aggregated on the flag leaf below the inflorescence, whereas R. padi occurred mostly on leaf sheaths. Predators again captured R. padi more often than D. noxia, and spent more time consuming aphids in the mixed-species treatment than in the pure-D. noxia treatment. These behavioral observations support the hypothesis that non-target prey can hamper the short-term effectiveness of biological-control agents against D. noxia.     

Cereal aphids on maize in southern England

In 1978, 1979 and 1980, counts were made of the numbers of cereal aphids on a maize crop near Fordingbridge, Hampshire, England. Maize plants were selected away from the edge of the crop and the number, morph, species and feeding site of the aphids were recorded. Metopolophium dirhodum and Rhopalosiphum padi were found at densities that exceeded those found on small-grain cereals and grasses at the same time of the year. Sitobion avenae and Macrosiphum euphorbiae were found at relatively low densities, and Rhopalosiphum maidis and Metopolophium festucae were observed rarely. Unlike other species, the numbers of R. padi continued to increase throughout the summer and reached a peak in September/October; at this time of the year, R. padi constituted over 98% of the aphids found on maize. M. dirhodum and S. avenae were found mostly on the leaves whereas R. padi appeared to favour the cob until populations became too large to be supported. If the area of maize grown in the UK increases, the crop will probably play an important role in the life cycle of cereal aphids (especially R. padi ). It is suggested that further work should be carried out on the pest status of aphids on maize and on the role that maize may play in the ecology of cereal pests.     

Contact with the host plant enhances aphid survival at low temperatures

1. The hypothesis, suggested by previous studies, that host plant contact reduces the cold tolerance of anholocyclic aphids was tested under laboratory conditions. Adult and first-instar Rhopalosiphum padi (L.) were exposed to temperatures of 0, –5 and –10 °C on intact plants, excised leaves and in the absence of contact with plant material.
2. Median lethal time (LT₅₀) values at all three temperatures indicate that aphids exposed in association with plant material survive longer than aphids that have no contact with their host plant. The difference in survival was most pronounced at –10 °C. Therefore, the above hypothesis is rejected for aphids on cereals because host plant contact apparently enhances cold tolerance.
3. Exposure on excised leaves also enhanced aphid survival at low temperature but was less effective than the intact plant. This suggests that plant quality as well as the presence or absence of plants is important in the cold tolerance of aphids on cereals.     

Quality of two aphid species (Rhopalosiphum padi and Sitobion avenae) as food for the generalist predator Tachyporus hypnorum (Col., Staphylinidae)

Abstract:  The quality of two aphid species ( Rhopalosiphum padi and Sitobion avenae ) as food for the staphylinid generalist predator Tachyporus hypnorum was investigated. Fruit flies ( Drosophila melanogaster ) were used as prey for comparison. T. hypnorum has been reported to prey on aphids, to consume large quantities and to show a high preference for aphids. This study showed that compared with fruit flies aphids are not high-quality prey for neither adult females nor larvae of T. hypnorum . Larvae were less able to utilize aphids than adult females. Reproduction was affected by both aphid species; a diet of S. avenae reduced fecundity, and a diet of R. padi reduced egg hatching success and prolonged the time spent in the egg stage compared with a fruit fly diet. For the T. hypnorum larvae pure diets of both S. avenae and R. padi resulted in high larval mortality. Overall ranking of the three prey types based on several fitness parameters differed between larvae and adults. The adult fitness parameters gave rather conflicting rankings of all three prey types though the two aphid species were of approximately the same overall value, whereas the larval fitness parameters gave identical rankings: D. melanogaster  >  S. avenae  >  R. padi . In the larval stage survival was greatly reduced by both aphid diets, while this was not the case for the adult females.     

Change in response of Rhopalosiphum padi spring migrants to the repellent winter host component methyl salicylate

Olfactometry showed that the response of spring migrants of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), to the repellent winter host volatile methyl salicylate changes with age of the adult aphid. Between three and four days after becoming adult, and having left the winter host Prunus padus L., aphids lost their negative response to the chemical. The change in response was not associated with contact with a summer host, oats. In a settling choice bioassay, migrants avoided oats which had been exposed to volatile methyl salicylate. Aphids with removed antennal tips did not avoid the exposed plant, indicating that plant choice was influenced by cues from the plant surface. The results are discussed in relation to the use of methyl salicylate in integrated control.     

Changes in activity of superoxide dismutase and catalase within cereal aphids in response to plant o-dihydroxyphenols

Abstract:  Superoxide dismutase and catalase activity was found in the bird cherry-oat aphid, Rhopalosiphum padi (L.) and the grain aphid, Sitobion avenae (F.). Among the aphid morphs studied, the highest activity of the antioxidant enzymes was noted for winged adults (alatae) and the lowest for wingless (apterae) ones. Higher activity of superoxide dismutase and catalase was observed in the polyphagous species R. padi that alternates between woody host plants and grasses. On some ocassions, activity of superoxide dismutase in cereal aphids was increased by twofold, when aphids were exposed to toxic plant o -dihydroxyphenols. An opposite tendency was observed in case of activity of the catalase that was strongly reduced within body of phenolics-treated insects. Among the plant allelochemicals studied, caffeic acid showed the strongest effect on the activity of the antioxidant enzymes of the cereal aphids. The experiments carried out indicate that antioxidant enzymes might play an important role in interactions between cereal aphids and their host plants.     

Reproduction and probing behaviour of the bird cherry‐oat aphid Rhopalosiphum padi on detached leaves and leaves on intact seedlings of the winter host,bird cherry Prunus padus

Video recording and electrical penetration graph techniques are used simultaneously to investigate host acceptance (in terms of reproduction) and probing activities of autumn migrants (gynoparae) of the bird cherry‐oat aphid Rhopalosiphum padi (L.) on detached leaves and on leaves on intact plants of the winter host, bird cherry Prunus padus. There are no significant differences between the times taken to first parturition or the number of nymphs produced over a 6‐ or 18‐h period on intact plants or detached leaves. Stylet probing activities (i.e. total probe duration, xylem ingestion, the time to first phloem contact and phloem salivation) are also similar in the two situations.     

Amino acid budgets in three aphid species using the same host plant

Abstract. Nutrient provisioning in aphids depends both on the composition of ingested phloem sap and on the biosynthetic capabilities of the aphid and its intracellular symbionts. Amino acid budgets for three aphid species, Rhopalosiphum padi (L.), Schizaphis graminum (Rondani) and Diuraphis noxia (Mordvilko), were compared on a single host plant species, wheat Triticum aestivum L. Ingestion of amino acids from phloem, elimination of amino acids in honeydew, and the content of amino acids in aphids tissue were measured. From these values, ingestion rates were estimated and compared to honeydew and to estimated composition of aphid proteins. Ingestion rate was lowest in D. noxia due to low growth rate and low honeydew production; intermediate in S. graminum due to higher growth rate and intermediate honeydew production; and highest in R. padi , which had the highest rates for both variables. Both D. noxia and S. graminum induced increases in the amino acid content of ingested phloem. These changes in phloem content, combined with differences in ingestion rates, resulted in large differences among aphids in estimated rates of ingestion of individual amino acids. In honeydew, most essential amino acids were found in low amounts compared with the amounts ingested, especially for methionine and lysine. A few amino acids (arginine, cystine, histidine and tryptophan) were more abundant in honeydew of some aphids, suggesting oversupply. Aphid species differed in the composition of free amino acids in tissue but showed very similar composition in protein, implying similar requirements among the aphids. In R. padi and D. noxia , most essential amino acids were ingested in amounts insufficient for growth, implying dependence on symbiont provisioning. In S. graminum , most amino acids were ingested in amounts apparently sufficient for growth.     

Chemical aspects of host‐acceptance behaviour in the bird cherry‐oat aphid Rhopalosiphum padi: host‐acceptance signals used by different morphs with the same genotype

Host acceptance by gynoparae and winged virginoparae of the bird cherry‐oat aphid Rhopalosiphum padi (L.) is investigated utilizing leaves and aqueous extracts of the primary and secondary hosts, as well as nonhost plants. Gynoparae are specialized to reproduce on bird cherry Prunus padus L., whereas virginoparae reproduce and feed on various grasses. Host acceptance is assessed using levels of reproduction and survival for adults, as well as survival for nymphs. Little is known of host acceptance by nymphs. The data show that gynoparae and winged virginoparae produce nymphs almost exclusively on their host plants, bird cherry and barley leaves, respectively, over 72 h. When tested with aqueous plant extracts, however, gynoparae produce nymphs almost exclusively on bird cherry extract and progeny numbers are found to be similar to those on plant leaves. Few nymphs are produced on artificial diet. By contrast, winged virginoparae produce nymphs on aqueous extracts of barley, bird cherry and bean, as well as on artificial diet. The numbers of nymphs deposited by gynoparae are similar on aqueous extracts of bird cherry leaves collected at different times during the growing season. When extracts from leaves of various Prunus species are tested, only leaves of P. padus and Prunus virginiana stimulate parturition. Oviparae, the sexual female nymphs of gynoparae, survive well for 96 h on both bird cherry and barley leaves but not on bean seedlings, whereas nymphs of winged virginoparae survive well only on barley leaves. They do not survive for 96 h on any plant‐leaf extracts, although they do survive on artificial diet.     

Triticum monococcum lines with distinct metabolic phenotypes and phloem‐based partial resistance to the bird cherry–oat aphid Rhopalosiphum padi

Crop protection is an integral part of establishing food security, by protecting the yield potential of crops. Cereal aphids cause yield losses by direct damage and transmission of viruses. Some wild relatives of wheat show resistance to aphids but the mechanisms remain unresolved. In order to elucidate the location of the partial resistance to the bird cherry–oat aphid, Rhopalosiphum padi, in diploid wheat lines of Triticum monococcum, we conducted aphid performance studies using developmental bioassays and electrical penetration graphs, as well as metabolic profiling of partially resistant and susceptible lines. This demonstrated that the partial resistance is related to a delayed effect on the reproduction and development of R. padi. The observed partial resistance is phloem based and is shown by an increase in number of probes before the first phloem ingestion, a higher number and duration of salivation events without subsequent phloem feeding and a shorter time spent phloem feeding on plants with reduced susceptibility. Clear metabolic phenotypes separate partially resistant and susceptible lines, with the former having lower levels of the majority of primary metabolites, including total carbohydrates. A number of compounds were identified as being at different levels in the susceptible and partially resistant lines, with asparagine, octopamine and glycine betaine elevated in less susceptible lines without aphid infestation. In addition, two of those, asparagine and octopamine, as well as threonine, glutamine, succinate, trehalose, glycerol, guanosine and choline increased in response to infestation, accumulating in plant tissue localised close to aphid feeding after 24 h. There was no clear evidence of systemic plant response to aphid infestation.     

Behavior of bird cherry-oat aphid and green peach aphid in relation to potato virus Y transmission

Potato virus Y is transmitted to potato in a nonpersistent manner by many aphid species, some of which do not colonize this crop. The behavior of bird cherry-oat aphid, Rhopalosiphum padi (L.) on potato, Solanum tuberosum L., a plant species that is not colonized by this aphid, was described and compared with that of the potato-colonizing green peach aphid, Myzuspersicae (Sulzer). A higher proportion of winged morph of R. padi than M. persicae left the plant, but aphids that stayed in contact with the plant took the same mean time to initiate the first probe and it lasted the same mean time compared with M. persicae. Electronic penetration graph technique was used to study the probing behavior of the aphids during Potato virus Y (family Potyviridae, genus Potyvirus, PVY) transmission tests. Transmission rate decreased from 29 to 8% when the acquisition time increased from 5 min of continuous probing to 1 h with M. persicae, but it remained low (2 and 1%) with R. padi. Most of the difference in transmission rate between acquisition time with M. persicae and between aphid species was related to the change in the time and behavior taking place between the last cell puncture of the acquisition phase to the first cell puncture of the inoculation phase. Results presented here clearly demonstrated the importance of host plant selection and probing behavior in the transmission of nonpersistent plant viruses. They also stress the need to consider the behavior of the aphid in the design of laboratory tests of virus vector efficacy.