Hydroxamic acids affecting barley yellow dwarf virus transmission by the aphid Rhopalosiphum padi

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid (Hx) occurring in wheat, was shown to deter feeding by the aphid Rhopalosiphum padi (L.), and to reduce BYDV transmission to the plant. Dual choice tests with wheat leaves showed the preferential settlement of aphids on leaves with lower levels of DIMBOA. Electric monitoring of aphid feeding behaviour showed that in seedlings with higher DIMBOA levels fewer aphids reached the phloem and they needed longer times to contact a phloem vessel than in those with lower levels. When aphids carrying BYDV were allowed to feed on wheat cultivars with different DIMBOA levels, fewer plants were infected with BYDV in the higher DIMBOA cultivars than in the lower ones. Preliminary field experiments showed a tendency for wheat cultivars with higher Hx levels to be more tolerant to infection by BYDV than lower Hx level ones.     

Effect of gramine on the feeding behavior of the aphids Schizaphis graminum and Rhopalosiphum padi

The effects of the indole alkaloid gramine on the behavior of the aphids Schizaphis graminum and Rhopalosiphum padi feeding on barley seedlings and on artificial diets were studied. On barley cv. F. Union, which lacks gramine, S. graminum ingested from phloem tissue for 30–80 min and non-phloem for 20–40 min, over a period of 3 h. In cultivar Datil S, gramine was found only in the epidermis and parenchyma mesophyll cells. On this cultivar, the non-phloem wave form of S. graminum was not observed. On F. Union, R. padi ingested non-phloem with short periods of ingestion from phloem. On cv. Datil S, this aphid did not show the non-phloem wave form. In experiments performed with cv. F. Union seedlings that contained exogenous gramine S. graminum did not ingest from phloem. Exogenous gramine was found only in the vascular bundles. It is suggested that gramine content and location may affect the feeding behavior of aphids in barley.

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Résumé Les effects de la gramine sur le comportement alimentaire des pucerons Schizaphis graminum et Rhopalosiphum padi on été étudiés en plantules d'orge (Hordeum distichum) et aussi avec des diètes artificielles à l'aide d'un moniteur électronique. S.graminum se nourri pendant 30–80 minutes à partir du phloème et il a pris 20–40 minutes en se nourrisant d'autres tissues divers, d'un total de 3 heures d'exposition à la plante. Dans la culture Datil S la gramine a été trouvée seulement dans les cellules de l'epidermis et du parenchyme du mesophyle. Dans ce cas, l'onde non-phloematique de S. graminum, n'a été pas observé; le temps pour le première onde X a été plus prolongé par rapport à la culture F. Union. Dans la culture F. Union, R. padi se nourri principalement de tissue non-phloematique (35–100 minutes) et du phloème par des brèves périodes (15–25 minutes). Dans le cas de la culture Datil S ce puceron n'a pas montré l'onde X. D'autre part, quand les plantules de F. Union ont été poussées dans des solution avec gramine, S. graminum ne se nourri pas du phloeme, tandis que R. padi montre un comportement similaire a celui-ce observé avec plantules sans gramine. La gramine absorbé par les plantules a été retrouvée seulement dans les faisceaux vasculaires. D'autre part, la gramine dans des diètes artificielles agit comme repulsif alimentaire à partir de concentrations de 0,5 mM. Avec des diètes contenant 3 mM de gramine l'alimentation des pucerons a été inhibée. Pourtant, ces resultats sugèrent que le contenuet et la localisation de la gramine peuvent modifier le comportement alimentaire des pucerons en plantules d'orge.

     

Role of an indole alkaloid in the resistance of barley seedlings to aphids

The content of the simple indole alkaloid gramine in barley leaves decreased with age. Conversely, susceptibility to aphids increased in older plants. Population growth rate of the greenbug Schizaphis graminum correlated with gramine content of leaves of several barley cultivars. Gramine decreased rate of feeding, survival and reproductive index of aphids feeding on artificial diets at concentrations similar to those found in plant leaves. Thus, it is suggested that gramine plays a role in the resistance of barley seedlings to S. graminum. Benzyl alcohol, a previously reported insect resistance factor from barley, was absent from all barley cultivars analysed.     

Diapause termination and egg hatch in the bird cherry aphid, Rhopalosiphum padi

Conclusion TastePROBE is a convenient and flexible electronic circuit designed to record action potentials from taste sensilla of insects. It facilitates the recording of slow potentials arising in taste sensilla, improves the signal to noise ratio, and preserves spike shapes. This new amplifier design combines excellent signal to noise ratio with complete compatibility as regards existing electrophysiological equipment.DC recordings have higher information content than filtered recordings. With DC recordings, spike shapes are not modified and thus better sorting is possible. Moreover, slow variations in the transepithelial potential (i.e. less than 10 Hz) are preserved. Both aspects are of considerable importance when studying the physiology of taste receptors.     

Feeding responses of two grain aphids to barley yellow dwarf virus-infected oats

The probing behavior of greenbugs, Schizaphis graminum (Rondani), and oat-bird cherry aphids, Rhopalosiphum padi (L.), was electronically monitored on healthy oats, Avena sativa (L.), and on oats infected with the RPV-NY isolate of barley yellow dwarf virus (BYDV). S. graminum fed better on infected oats than on healthy oats. This was manifested by a shorter time before initiation of committed phloem ingestion, and by increased duration of ingestion from phloem of infected compared to healthy plants. In addition, on infected oats S. graminum made fewer interruptions in their probing once their stylets were inserted into tissues, including phloem. R. padi fed similarly on infected and healthy oats, except that these aphids made fewer short probes to the phloem (lasting <15 min) on infected compared to healthy oats. BYDV infection of oats increased the rate of population growth of S. graminum relative to that on healthy oats but had no effect on the population growth of R. padi. The proportion of aphids of R. padi which developed into alatae on BYDV-infected oats was significantly greater than on healthy oats, but S. graminum showed no such response.

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Résumé Le comportement de sondage de S. graminum (Rond.) et de R. padi (L.) a été suivi électroniquement sur avoine (Avena sativa L.) saine ou contaminée par l'extrait RPV-NY du virus jaune du nanisme de l'orge (BYDV). S. graminum s'est mieux alimenté sur avoine contaminée que saine; ceci se traduisait par un temps de latence inférieur avant l'ingestion de phloème et par une prolongation de la période d'ingestion. De plus, sur avoine contaminée, S. graminum a moins souvent interrompu le sondage, une fois que les stylets avaient étè insérés dans les tissus, y compris le phloème. Les résultats avec R. padi présentaient les mêmes tendances, mais les améliorations des performances alimentaires de cette espèce sur avoine contaminée ont été moins nettes que pour S. graminum. La contamination de l'avoine par BYDV a accru le taux de croissance de la population de S. graminum par rapport à ce qui a été observé sur avoine saine; l'effet était moins prononcé pour R. padi. La proportion de pucerons devenant aliés était plus élevée sur avoine contaminée que saine, rien de tel n'a été observé avec S. graminum.

     

Identifying bird cherry-oat aphid Rhopalosiphum padi emigrants, alate exules and gynoparae: application of multivariate methods to morphometric and anatomical features

The host microhabitat location behavior of females of the generalist parasitoid Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) was studied in a wind tunnel. Visual cues associated with the host plant cotton, Gossypium hirsutum L., were important and significantly more parasitoids completed flights to a damaged 4-leaf cotton plant bearing a Heliothis virescens (F.) (Lepidoptera: Noctuidae) larva and frass than to a similarly damaged single leaf with frass and a larva. This difference in completed flights was not due to differences in amounts of volatiles released by the two stimuli. Both naive and experienced parasitoids responded differently to an undamaged cotton leaf, a mechanially damaged leaf, a naturally damaged leaf with the host removed and a naturally damaged leaf with a host larva. Parasitoids completed significantly fewer flights to the undamaged sources of volatiles than to damaged sources of volatiles. Experienced females responded strongly to all types of damage. The number of flights completed by naive females to the three types of damage differed but not significantly and was less than the number completed by experienced females. Components of the preflight experience were varied to determine which factors were responsible for the higher response of experienced females to the host/plant complex. Oviposition was the most important component of this experience. Contact with host frass or plant damage followed by oviposition did not increase the response over that exhibited by females allowed oviposition only. When frass or damaged plant material were contacted without subsequent oviposition, females completed fewer flights than naive females.     

Effect of epigeal predators on infestation by the aphid Rhopalosiphum padi and on grain yield of oats in monocrops and mixed intercrops

Three field experiments, with factorial designs and consisting of monocrops of oats, Avena sativa, and mixtures of oats with faba bean, Vicia faba, were conducted in 1983–1985. The densities of generalist epigeal predators were manipulated by vertical barriers or ingress and egress trenches. Pitfall trapping was used to measure the effect of manipulation. Tillers were sampled to monitor populations of the major pest of oats, the bird cherry-oats aphid, Rhopalosiphum padi, and to estimate their peak densities. Also grain yields were measured.The barriers and the egress trenches significantly reduced the pitfall catches of carabids, staphylinids and spiders. The effect on Coccinella septempunctata was variable. The peak aphid densities were 11–125% higher in the predator reduction treatments than in the controls. The grain yields of oats were reduced by 19–22% in all cases where aphid densities were increased by the manipulations. Relief of predation pressure by generalist epigeal predators is the proposed explanation for the increased R. padi densities and subsequently decreased oat yields.Mixed cropping increased the pitfall catches of carabids by 14–36%. Trechus spp. contributed most to the pattern. In 1985 the early egress manipulation increased the aphids' peak density and decreased the yield of oats significantly more in the monocrop than in the mixture: this was thought to be because the R. padi population escaped predation as the result of a higher colonization rate in the mixture, rather than being due to responses of the predators to crop diversification.

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Résumé Trois expériences en plein champ ont été réalisées en Finlande en 1983–85 pour étudier l'influence des prédateurs épigés sur le niveau de contamination par R. padi et la production de grains d'avoine en cultures pures ou associées à Vicia faba. R. padi est le principal ravageur de l'avoine dans ce système. Les captures réalisées par les prédateurs épigés, principalement des carabidae, des staphylinidae et des araignées ont réduit les attaques dans les parcelles entourées de barrières verticales (1983) ou de fossés inondés. Les réactions de Coccinella septempunctata à ces manipulations ne sont pas constantes et ne peuvent pas expliquer son influence sur les populations de R. padi. Les densités maximales de pucerons ont été de 11 à 125% élevées dans les parcelles modifiées que dans les parcelles témoins ou entourées de fossés inondés. Les récoltes d'avoine ont été réduites de 19 à 22% dans tous les cas où la densité de pucerons a augmenté.Dans la discussion, la limitation de la pression de prédation par les généralistes épigés a été mise en avant pour expliquer l'augmentation des densités de R. padi et la diminution consécutive de la récolte d'avoine. La comparaison des caractéristiques du système R. padi avoine de printemps et du système R. padi/blé d'hiver laisse supposer qu'elles ont contribué à la relative importance des prédateurs généralistes consommant R. padi tôt dans la saison.Ces résultats ne suggèrent aucun effet négatif de la culture mixte avec V. faba sur la prédation épigée. Cependant, des éléments montrent qu'une forte densité de colonisation par des immigrants ailés de R. padi dans les cultures peut permettre à la population proie d'échapper aux prédateurs généralistes quand ceux-ci deviennent saturés aux densités de proies élevées. On peut en conclure que la contribution potentielle des prédateurs épigés aux récoltes de céréales de printemps,-qui ne se rlise que lorsque R. padi n'est pas limité d'une autre façon-, dépend du niveau atteint par la première colonisation par R. padi ailés. Leur contribution est la plus faible lors d'une très faible ou d'une très forte colonisation.

     

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.     

Mixing barley cultivars affects aphid host plant acceptance in field experiments

Four barley varieties with no significant difference in aphid acceptance were sown in pure stands and in pairwise combinations with varieties side by side in separate rows. Settling tests were done in situ in the field plots with apterae of Rhopalosiphum padi (L.) (Homoptera:Aphididae) and showed that aphid acceptance was changed in some combinations of cultivars. In a laboratory test, in which plants of one cultivar were exposed to air from the other cultivars, aphid acceptance was significantly reduced in three of the four cultivars when treated with air from certain other cultivars. Two of these three cultivars showed the same reduction under field conditions. This supports the hypothesis that plant/plant communication may release responses in neighbouring plants that change aphid host plant acceptance. The results also show that this mechanism is not restricted to optimal growing conditions in the laboratory, although it may be modified under field conditions depending on plant genotype.     

Abscisic acid and jasmonic acid affect proteinase inhibitor activities in barley leaves

Proteinase inhibitor (PI) accumulation has been described as a plant defense response against insects and pathogens. The induction of PIs is known to be regulated by endogenous chemical factors including phytohormones. We studied the induction of barley chymotrypsin and trypsin inhibitory activities by aphid infestation, mechanical wounding, abscisic acid (ABA) and jasmonic acid (JA). Wounding experiments led to a minimal accumulation of PI activity (16% over controls) compared to that found in barley seedlings infested by aphids, where chymotrypsin inhibitor activity showed a two-fold increment. No systemic induction could be detected in healthy leaves of an infested or mechanically injured plant. Exogenous ABA applied on barley leaves increased the chymotrypsin inhibitory activity, while JA only increased trypsin inhibitory activity locally and systemically when applied exogenously. Our data suggest that two different mechanisms may be regulating the induction of these two types of inhibitors.     

Microarray analysis of the interaction between the aphid <Emphasis Type="Italic">Rhopalosiphum padi</Emphasis> and host plants reveals both differences and similarities between susceptible and partially resistant barley lines

The bird cherry-oat aphid (Rhopalosiphum padi L.) is an important pest on cereals causing plant growth reduction without specific leaf symptoms. Breeding of barley (Hordeum vulgare L.) for R. padi resistance shows that there are several resistance genes, reducing aphid growth. To identify candidate sequences for resistance-related genes, we performed microarray analysis of gene expression after aphid infestation in two susceptible and two partially resistant barley genotypes. One of the four lines is a descendant of two of the other genotypes. There were large differences in gene induction between the four lines, indicating substantial variation in response even between closely related genotypes. Genes induced in aphid-infested tissue were mainly related to defence, primary metabolism and signalling. Only 24 genes were induced in all lines, none of them related to oxidative stress or secondary metabolism. Few genes were down-regulated, with none being common to all four lines. There were differences in aphid-induced gene regulation between resistant and susceptible lines. Results from control plants without aphids also revealed differences in constitutive gene expression between the two types of lines. Candidate sequences for induced and constitutive resistance factors have been identified, among them a proteinase inhibitor, a serine/threonine kinase and several thionins. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Discovery and molecular characterization of a plasmid localized in Buchnera sp. bacterial endosymbiont of the aphid Rhopalosiphum padi

We have identified and completely sequenced a novel plasmid isolated from the aphid Rhopalosiphum padi. Evidence which suggests that the plasmid occurs localized within the bacterial endosymbionts is presented. The plasmid contains the four genes that constitute the entire leucine operon. This fact makes it really unique since most plasmids are dispensable and lack genes that encode essential anabolic functions. Four more phloem-feeding aphid species also seem to contain homologous plasmids.Although further work is necessary, we hypothesize that this plasmid has appeared during the evolution of the symbiotic association between the aphid and the bacterial endosymbiont. The fact that this plasmid contains the entire leucine operon can be related to physiological evidence showing that the aphid host's diet of plant phloem is deficient in essential amino acids.     

Fitness comparison between clones differing in their ability to produce sexuals in the aphid Thopalosiphum padi

This study aimed at evaluating the intrinsic rate of increase (r _m ) of clones of the cereal aphid Rhopalosiphum padi (L.) that differ in their ability to produce sexuals. The value of r _m was measured for wingless parthenogenetic females in experiments conducted at two temperatures (15 °C and 20 °C). We studied six holocyclic clones, five androcyclic clones and five anholocyclic clones and showed that life-cycle has no significant effect on the age at first reproduction, on fecundity nor on longevity. As a result there is no influence on (summer) fitness: on the one hand, holocyclic clones do not compensate their lower fitness in mild winters by a higher fitness during the summer. On the other hand, anholocyclic and androcyclic clones do not seem to obtain any advantage from living on a more restricted range of hosts: there appears to be no cost of polyphenism for holocyclic clones.     

Non-feeding by adult gynoparae of Rhopalosiphum padi and its bearing on the limiting resource in the production of sexual females in host alternating aphids

Radioactive plants were used to determine whether gynoparae of the bird cherry-oat aphid Rhopalosiphum padi (L.) fed after settling on Prunus padus (L.). Despite being starved for 24 h they did not feed. The adaptive significance of the short adult life and low fecundity of gynoparae was discussed in the light of these results.

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La consommation des synopares adultes de Rhopalosiphum padi et son importance sur la limitation des resources dans la production de femelles sexuées chez les pucerons à hôtes alternatifs

Résumé Des plantes radioactives ont été utilisées pour déterminer si les gynopares de Rhopalosiphum padi se nourrissaient après installation sur Prunus padus. Bien qu'affamés pendant 24 h, il ne se sont pas nourris. La signification adaptative de la brève vie des adultes et de la faible fécondité des gynopares a été examinée à la lumière de ces résultats.

     

Host plant selection by migrant Rhopalosiphum padi in autumn and the occurrence of an intermediate morph

Alate female Rhopalosiphum padi (L.) were trapped alive in suction traps in autumn, 1986–1988. Alate exules and gynoparae were identified by the morph of their offspring. Gynoparae largely replaced alate exules in September indicating that most of the population were holocyclic even in southern England where the primary host, Prunus padus L., is scarce. However, a few alate exules occurred throughout the autumn indicating that a proportion of the population is anholocyclic. A morph intermediate between alate exules and gynoparae occurred at low frequency throughout the autumn. Alate exules and gynoparae preferred barley and P. padus, respectively, on which to settle and larviposit; gynoparae were less selective than exules possibly due to an incomplete physiological switch from a preference for Gramineae to P. padus on which the sexual cycle is completed. Intermediate individuals preferred to settle on P. padus, but their virginoparous and oviparous nymphs were produced on barley and P. padus respectively. Intermediate morphs maintained under continuous short day conditions (L12 : D12) produced mainly apterous virginoparae with males occurring at the end of their reproductive live; intermediates occurred occasionally amongst the apterae. It is proposed that intermediates are a programmed component of the morph structure and have the potential to contribute to both the holocyclic and anholocyclic portions of the population.

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Résumé Des femelles de R. padi L. ont été capturées vivantes dans des pièges a succion en 1986–88. Les ailés exules et les gynopares ont été identifiés par le morphe de leurs descendants. Les gynopares ont remplacé généralement les ailés exules en septembre, ce qui montre que la majorité de la population est holocyclique même dans le sud de l'Angleterre où l'hôte primaire, Prunus padus L., est rare. Cependant, quelques ailés exules se maintiennent pendant l'automne montrant qu'une partie de la population est anholocyclique. Au cours de l'automne, on observe un morphe intermédiaire entre les ailés exules et les gynopares. Les exules ailés et les gynopares préfèrent respectivement l'orge et P. padus, sur lesquels ils s'installent et produisent des larves; les gynopares étaient moins sélectifs que les exules, peut-être par suite d'une rupture physiologique incomplète de leur préférence pour l'orge sur laquelle ils se développent rendant moins impérative leur attraction par P. padus sur lequel leur cycle sexuel est complet. Les individus intermédiaires préfèrent s'établir sur P. padus, mais leur larves virginipares et ovipares sont produites respectivement sur oreg et sur P. padus. Les morphes intermédiaires maintenus en jours courts (L12/N12) ont donné surtout des virginipares aptères les mâles apparaissant à la fin de leur vie; des intermédiaires sont apparus occasionnellement parmi les aptères. Les intermédiaires seraient une composante programmée de la structure polymorphe et contribueraient à la fois à l'apparition des fractions holocyclique et anholocyclique de la population.

     

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.     

The influence of clone and morph on the parameters of intrinsic rate of increase in the cereal aphids Sitobion avenae and Rhopalosiphum padi

This study aimed at evaluating the influence of intrinsic factors (clone, morph) on the parameters of the intrinsic rate of increase of Sitobion avenae (F.) and Rhopalosiphum padi (L.). For each species, apterous and alate exules of three clones originating from French oceanic regions were compared at 20 °C.The clonal factor had a significant effect on both time from birth until onset of reproduction (TBR) and intrinsic rate of increase (r). This effect was lower than that of the morph. Moreover, in the case of R. padi, a strong clone-morph interaction was observed.Both apterous and alate morphs were shown to have a higher rate of increase in R. padi than in S. avenae.Various models were fitted to aphid daily rate of reproduction. Both types of model and quality of fit depended mainly on the morph.

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Résumé Cette étude a eu pour but d'évaluer l'importance de facteurs intrinsèques (clone et morphe) sur les paramètres du taux d'accroissement de Sitobion avenae (F.) et Rhopalosiphum padi (L.).Pour chaque espèce, trois clones originaires de régions océaniques françaises ont été comparés à 20 °C pour les morphes exules ailés et exules aptères.L'effet du clone est significatif sur l'âge reproducteur (durée comprise entre la naissance du puceron et le début de sa phase de reproduction) et sur le taux intrinsèque d'accroissement naturel. Il est plus faible que celui du morphe avec lequel il intéragit dans le cas de R. padi.Les différences interspécifiques relevées mettent en évidence les capacités d'accroissement supérieures de R. padi par rapport à celles de S. avenae, dans le cas des ailés comme dans celui des aptères.Enfin, différents modèles ont été appliqués aux données de reproduction journalière des pucerons. Le type et la qualité des ajustements varient essentiellement en fonction du morphe.

     

The potential of hydroxamic acids in tetraploid and hexaploid wheat varieties as resistance factors against the bird‐cherry oat aphid,Rhopalosiphum padi

The potential for exploiting natural wheat resistance to control the cereal aphid Rhopalosiphum padi, the most important aphid pest of small grain cereals in the UK, was investigated as an alternative approach to the use of insecticides. The investigation focussed on a group of secondary metabolites, the hydroxamic acids or benzoxazinones, present naturally as glucosides, but which hydrolyse on tissue damage to give biologically active aglycones, e.g. 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA) which are associated with natural plant defence. These can be important for resistance against insects, fungi, bacteria and nematodes for a range of cultivated monocotyledonous plants and could ultimately be combined with other defence mechanisms to provide a general approach to cereal aphid control. Levels of hydroxamic acids, particularly DIMBOA‐glucoside, were determined in hexaploid (Triticum aestivum) and tetraploid (Triticum durum) wheat varieties and differences were found between species and varieties. The effect of feeding by R. padi on the level of hydroxamic acids in the leaf tissue was also investigated. Thus, after 24 h of aphid feeding, as an apparently localised hydrolytic defence reaction in the leaf, levels of DIMBOA‐glucoside decreased noticeably. When aphids were fed on sucrose solution containing low doses of DIMBOA there was a significant mortality compared to the sucrose control. However, the levels of and variation in hydroxamic acids in the wheat varieties investigated were insufficient for significant differences in aphid behaviour and development.     

A method for hatching the eggs of the aphid Schizaphis graminum

Techniques are described for the collection of fertile eggs of Schizaphis graminum (Rond.) on filter paper, and for the subsequent sterilization and incubation of the eggs under various temperature and photoperiodic conditions.19% of the eggs incubated continuously at 16°C in complete darkness hatched in 81 days after deposition. 45% of the eggs chilled at 6°C for 40 days (starting 10 days after deposition) hatched in 71 days if the postchilling incubation at 16°C was completed in darkness. The results indicate a further enhancement in the percentage egg hatch and a reduction in developmental time when the eggs were subjected to a light-dark regime during the post-chilling incubation.

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Zusammenfassung Es wird eine einfache und effektive Methode beschrieben, die Eier von Schizaphis graminum auf Filterpapier zu sammeln, sie nachfolgend zu sterilisieren und unter verschiedenen Temperatur- und Photoperiodebedingungen bis zum Schlüpfen zu inkubieren.Hierbei wurden folgende Resulate erzielt: (a) Inkubation der Eier in vollkommener Dunkelheit bei 16°C führte zu einem Schlupferfolg von 19% nach einer Entwicklungszeit von im Mittel 81 Tagen; (b) Kühlung der Eier bei 6°C während 40 Tagen (vom 10. Tag nach der Eiablage an) erhöhte die Schlupfrate unter ansonsten gleichen Bedingungen auf 45% und reduzierte die Entwicklungszeit auf 71 Tage; (c) durch einen Licht/Dunkel-Rhythmus, dem die Eier nach der 40-tägigen Kühlung ausgesetzt wurden, konnte eine weitere Steigerung der Schlupfrate und eine Verkürzung der Entwicklungszeit erreicht werden.