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.     

The life-cycle and host preferences of the bird cherry-oat aphid, Rhopalosiphum padi L., and their bearing on the theories of host alternation in aphids

Emigrants of the host-alternating bird cherry-oat aphid fly from the primary host to various grasses before the end of June, even in the absence of natural enemies on bird cherry. They fly before the leaves of bird cherry mature and at a time when numbers of insect predators are rapidly increasing. In the autumn gynoparae and males return to bird cherry whose senescing leaves again provide the aphids with a rich source of food. The growth efficiency of R. padi on bird cherry and oats indicates that the quality of the available food on the two hosts is markedly different.
Apterous exules prefer oats to young bird cherry leaves and survive best on oats. Gynoparae prefer bird cherry leaves and only successfully produce offspring on the primary host. This, and other work published on R. padi , support the premise that a change in the aphid's preferences causes the change of host.
The dual-discrimination theory of host alternation in aphids is examined in the light of this and other published work.     

Oxidative responses of resistant and susceptible cereal leaves to symptomatic and nonsymptomatic cereal aphid (Hemiptera: Aphididae) feeding.

The impact of the leaf-chlorosis-eliciting Russian wheat aphid, Diuraphis noxia (Mordvilko), and the nonchlorosis-eliciting bird cherry-oat aphid, Rhopalosiphum padi (L.), feeding on D. noxia-susceptible and -resistant cereals was examined during the period (i.e., 3, 6, and 9 d after aphid infestation) that leaf chlorosis developed. After aphid number, leaf rolling and chlorosis ratings, and fresh leaf weight were recorded on each sampling date, total protein content, peroxidase, catalase, and polyphenol oxidase activities of each plant sample were determined spectrophotometrically. Although R. padi and D. noxia feeding caused significant increase of total protein content in comparison with the control cereal leaves, the difference in total protein content between R. padi and D. noxia-infested leaves was not significant. Although R. padi-feeding did not elicit any changes of peroxidase specific activity in any of the four cereals in comparison with the control leaves, D. noxia feeding elicited greater increases of peroxidase specific activity only on resistant 'Halt' wheat (Triticum aestivum L.) and susceptible 'Morex' barley (Hordeum vulgare L.), but not on susceptible 'Arapahoe' and resistant 'Border' oat (Avena sativa L.). D. noxia-feeding elicited a ninefold increase in peroxidase specific activity on Morex barley and a threefold on Halt wheat 9 d after the initial infestation in comparison with control leaves. Furthermore, D. noxia feeding did not elicit any differential changes of catalase and polyphenol oxidase activities in comparison with either R. padi feeding or control leaves. The findings suggest that D. noxia feeding probably results in oxidative stress in plants. Moderate increase of peroxidase activity (approximately threefold) in resistant Halt compared with susceptible Arapahoe wheat might have contributed to its resistance to D. noxia, whereas the ninefold peroxidase activity increase may have possibly contributed to barley's susceptibility. Different enzymatic responses in wheat, barley, and oat to D. noxia and R. padi feeding indicate the cereals have different mechanisms of aphid resistance.     

Movement by mating females of a host alternating aphid: a response to leaf fall

Autumn remigrants of the host alternating bird cherry-oat aphid, Rhopalosiphum padi , colonise individual plants of the winter host, Prunus padus . However, they do not select leaves at different stages of senescence, which is surprising as leaf fall is a definitive deadline for production and development of mating females. For successful development mating females should be mobile and have the capacity to evaluate leaf senescence. Although remigrants do not selectively colonise leaves at different stages of senescence, mating females were found in very low numbers on leaves that were about to be shed. In choice test and olfactometer bioassays, abscising leaves were avoided by mating females. In the field mature leaves were available for colonisation during the period of leaf fall of P. padus . We conclude that mating females abandon abscising leaves in favour of leaves at an earlier stage of senescence, increasing the time available for mating. Our results support the role of remigrants as pioneers which identify good winter host plants, and of mating females as mobile searchers for optimal feeding and mating sites.     

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.     

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.     

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.     

Diuraphis noxia and Rhopalosiphum padi (Hemiptera: Aphididae) interactions and their injury on resistant and susceptible cereal seedlings

Interspecific interactions between the symptomatic (chlorosis-eliciting) Russian wheat aphid, Diuraphis noxia (Mordvilko), and the asymptomatic (nonchlorosis-eliciting) bird cherry-oat aphid, Rhopalosiphum padi (L.), on four cereal genotypes were examined by simultaneous infestations. Four cereals (i.e., Diuraphis noxia-susceptible 'Arapahoe' wheat and 'Morex' barley, and D. noxia-resistant 'Halt' wheat and 'Border' oat) and four infestations (i.e., control, D. noxia, R. padi, and D. noxia/R. padi) were used in the research. Whereas D. noxia biomass confirmed D. noxia resistance among the cereals, R. padi biomass indicated that the D. noxia-resistant cereals did not confer R. padi resistance. D. noxia biomass was significantly lower in D. noxia/R. padi infestation than that in D. noxia infestation on all cereals, except Border oat, which indicated an antagonistic effect of R. padi on D. noxia. All aphid infestations caused a significant plant biomass reduction in comparison with the control. In comparison with D. noxia infestation, D. noxia/R. padi caused a significant plant biomass reduction on all cereals, except Morex barley. Although D. noxia biomass in D. noxia/R. padi infestation was significantly less than that in D. noxia infestation, leaf chlorophyll reduction was the same between D. noxia/R. padi and D. noxia infestations, which suggested that the asymptomatic R. padi enhanced the D. noxia-elicited leaf chlorophyll loss. The regression between chlorophyll content and aphid biomass indicated that the asymptomatic R. padi in the D. noxia/R. padi infestation enhanced chlorophyll loss, but interspecific aphid interaction on plant biomass varied among the cereals.     

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.     

禾谷缢管蚜在三个小麦品种上取食行为的EPG比较

应用刺探电位图谱（EPG）技术对禾谷缢管蚜Rhopalosiphum padi在不同小麦品种(Ww2730、小偃22和Batis)苗期的取食行为进行了比较研究。结果表明：在小偃22上蚜虫开始取食的第1次刺探时间最晚,且持续时间最短;在Ww2730上取食受到机械阻力的个体最多,且出现F波的几率和持续时间最长;两品种上蚜虫在木质部主动摄取汁液（G波）花费的时间最长。 在Batis上,蚜虫口针第1次到达韧皮部时需要分泌较多水溶性唾液(E1波),但随后只需分泌较少的水溶性唾液就可以成功取食,而且被动吸食韧皮部汁液的时间（E2波）最长。蚜虫口针在到达小偃22韧皮部取食之前,出现多次的口针试探、回撤,并且多次、多量分泌水溶性唾液（E1波）;虽然蚜虫在小偃22上口针最先到达韧皮部,但被动吸食韧皮部汁液的时间（E2波）最短。由此得出结论：小偃22表皮部、韧皮部存在阻碍禾谷缢管蚜取食的物理和生化因素; 禾谷缢管蚜在Ww2730取食遇到更多的是细胞间机械阻力; Batis是较感蚜的品种。     

A test of the coevolution theory of autumn colours: colour preference of Rhopalosiphum padi on Prunus padus

According to the coevolution theory of autumn colours, the bright colours of trees evolved as a warning signal towards parasites colonizing the plant in autumn. We monitored colonization of the aphid Rhopalosiphum padi on individual tress of Prunus padus in autumn and observed a strong preference of aphids for trees with green leaves. This is the first direct observation of a key assumption of the theory, that parasites avoid bright colours. Moreover our observations, compared with previous data gathered on the same species, suggest that aphids colonizing trees with green leaves develop better in spring than aphids colonizing trees with bright autumn colours, which is consistent with the second main assumption of the coevolution theory.     

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.     

麦长管蚜和禾谷缢管蚜对小麦植株挥发物及蚜害诱导挥发物的行为反应

用四臂嗅觉计测定了麦长管蚜Macrosiphum avenae和禾谷缢管蚜Rhopalosiphum padi对小麦植株挥发物及麦蚜取食诱导挥发物的行为反应,揭示了2种麦蚜的嗅觉及小麦植株的诱导防御反应特点.在所选的13种小麦植株挥发物及蚜害诱导挥发物组分中,6-甲基-5-庚烯-2-酮、6-甲基-5-庚烯-2-醇和水杨酸甲酯对这2种蚜虫表现出强的驱拒作用;反-2-己烯醛对麦长管蚜的有翅和无翅蚜的吸引作用最强;反-2-己烯醇对禾谷缢管蚜的无翅蚜吸引作用最强,反-3-己酰醋酸酯对禾谷缢管蚜有翅蚜的吸引作用最强.说明麦蚜取食能诱导小麦植株的防御反应,麦长管蚜和禾谷缢管蚜及其不同蚜型间嗅觉反应的特点不同.     

Life history of the bird cherry-oat aphid, Rhopalosiphum padi, on transgenic and non-transformed wheat challenged with Wheat streak mosaic virus

The life history of the bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), was studied via laboratory assays on Wheat streak mosaic virus (WSMV)-infected and non-infected transgenic and non-transformed wheat [ Triticum aestivum L. (Poaceae)]. Although R. padi is not a WSMV vector, it is known to colonize WSMV-infected wheat plants. Two transgenic soft white winter wheat genotypes, 366-D03 and 366-D8, that express the WSMV coat protein gene, and the WSMV-susceptible non-transformed cultivar Daws were tested. All genotypes showed disease symptoms when infected with WSMV. Whereas plant height was significantly reduced on virus-infected compared to non-infected plants of all genotypes, virus-infected transgenic plants exhibited lower virus titer and lower disease rating scores than Daws. No significant effects of WSMV infection or genotypes were observed on the length of R. padi nymphal development period, nor on their pre-, and post-reproductive periods. Rhopalosiphum padi reproductive period was significantly longer on Daws infected with WSMV than on non-infected plants of this cultivar. In contrast, there were no significant differences in length of R. padi reproductive period between virus-infected and non-infected transgenic plants within a genotype. Rhopalosiphum padi daily fecundity was significantly lower and adult longevity significantly longer on virus-infected than on non-infected plants of all genotypes. Total aphid fecundity and intrinsic rate of increase were not significantly different among treatments. The percentage of winged aphids that developed was greater on WSMV-infected compared to non-infected plants within a genotype. Results indicate that both virus infection status of plants and wheat genotype influence the life history of R. padi.     

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.     

Assessment of aphid lethal paralysis virus as an apparent population growth‐limiting factor in grain aphids in the presence of other natural enemies

The influence of aphid lethal paralysis virus (ALPV), Rhopalosiphum padi virus (RhPV), natural enemies and fungal infection on the population growth of Rhopalosiphum padi and Sitobion avenae in the wheat fields of the Western Cape Province of South Africa was investigated at two sites. Time‐specific life tables were compiled for R. padi at one site. During the logarithmic phase of the development of R. padi aphids, natural enemies were not present in high numbers and the apparent large‐scale mortality observed appeared to be due to other causes. During the decline phase of this aphid population, the population size was reduced by 49%. This reduction coincided with a calculated high mortality of 70 aphids per plant. A dramatic decline in R. padi numbers and a high incidence of ALPV present in the aphid population was experienced during this period. Virus assays were carried out by double‐antibody sandwich enzyme‐linked immunosorbent assay (DAS‐ELISA) and an indirect immunofluorescent technique. Entomophthorales‐type fungal infection of aphids also reached its highest level during the decline phase, but at a later stage than ALPV infection, with a calculated level of 21 aphids per plant. This suggested that the presence of ALPV limited population development in R. padi. Similar results were obtained with S. avenae.     

Host choice by Aphidius colemani: effects of plants, plant–aphid combinations and the presence of intra-guild predators

Abstract.  1. This study first measured the effect of plant (radish, pepper, and wheat), aphid–plant combination (the green peach aphid Myzus persicae on pepper and radish, and the bird cherry-oat aphid Rhopalosiphum padi on wheat) and the host on which Aphidius colemani was reared (the cotton aphid Aphis gossypii on cucumber, M. persicae on radish and pepper, and R. padi on wheat) on host choice behaviour of the parasitoid and the performance of its offspring. Then, the effect of predator presence ( Coccinella undecimpunctata larvae) on host preference of the wasps was tested.
2. When reared on M. persicae on either radish or pepper , wasps preferred the aphid–plant combination from which they had emerged. Wasps reared on A. gossypii (naïve to all hosts offered) and R. padi preferred to parasitise M. persicae on radish and M. persicae on either radish or pepper, respectively. Rhopalosiphum padi on wheat was the least preferred and also the least suitable host, as determined by offspring body size.
3. Contrary to expectations, the presence of predators did not influence the host choice of A. colemani , even when predator-free plants were offered nearby. Results indicate that wasps are more likely to remain in some host systems but not in others, even when facing risk of predation.
4. Results are discussed in respect to field data and the relative importance of risk of predation and host preference to wasp fitness.     

Barley exposed to aerial allelopathy from thistles (Cirsium spp.) becomes less acceptable to aphids

Abstract.  1. Recent studies have shown that plant–plant interaction via chemicals (allelopathy) can affect insects. Here the effects on aphid acceptance of barley after exposure to volatiles and root exudates from two common weeds, the thistles Cirsium arvense and Cirsium vulgare , were investigated.
2. Settling by bird cherry-oat aphid, Rhopalosiphum padi , was significantly reduced on barley plants that had been exposed to volatiles from Cirsium species for 5 days. Settling by Sitobion avenae was also reduced on Cirsium -exposed plants, whereas settling by Metopolophium dirhodum was not.
3. In olfactometer tests, Cirsium -exposed barley was significantly less attractive to R. padi than was unexposed barley, indicating that exposure causes a change in the volatile profile of barley.
4. Exposure of barley to root exudates from Cirsium species had no effect on R. padi settling.
5. The results lend weight to the theory that the effects of plant–plant allelopathy can extend to higher trophic levels.     

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.