Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.     

Molecular-genetic evidence of aphid pathogen Pandora kondoiensis infection in Sitobion avenae collected in Denmark

Entomophthoralean-specific primers were used to estimate the occurrence of entomophthoralean species in the cereal aphid Sitobion avenae in Denmark. Sequencing documented for the first time the presence of Pandora kondoiensis in Denmark. Specific primers were designed and P. kondoiensis was identified on 12% of infested straws sampled in 2012.     

SUPPRESSING A PEROXIDASE GENE REDUCES SURVIVAL IN THE WHEAT APHID Sitobion avenae

Peroxidases (POXs) make up a large superfamily of enzymes that act in a wide range of biological mechanisms, including maintaining appropriate redox balances within cells, among other actions. In this study, we cloned a sequence that encodes a POX protein, SaPOX, from wheat aphids, Sitobion avenae. Amino acid sequence alignment showed the SaPOX sequence was conserved with POXs from other insect species. SaPOX mRNA accumulations were present in all nymphal and adult stages, at higher levels during the first and second instar, and lower during later stages in the life cycle. Ingestion of dsRNA specific to POX led to reduced SaPOX mRNA accumulation. Sitobion avenae nymphs continuously exposed to dietary dsPOX via an artificial diet led to reduced survival rate and ecdysis index. We infer that POX is important to maintain the growth and development of S. avenae.     

Extending the half-life of a fab fragment through generation of a humanized anti-human serum albumin Fv domain: An investigation into the correlation between affinity and serum half-life

We generated an anti-albumin antibody, CA645, to link its Fv domain to an antigen-binding fragment (Fab), thereby extending the serum half-life of the Fab. CA645 was demonstrated to bind human, cynomolgus, and mouse serum albumin with similar affinity (1–7 nM), and to bind human serum albumin (HSA) when it is in complex with common known ligands. Importantly for half-life extension, CA645 binds HSA with similar affinity within the physiologically relevant range of pH 5.0 – pH 7.4, and does not have a deleterious effect on the binding of HSA to neonatal Fc receptor (FcRn). A crystal structure of humanized CA645 Fab in complex with HSA was solved and showed that CA645 Fab binds to domain II of HSA. Superimposition with the crystal structure of FcRn bound to HSA confirmed that CA645 does not block HSA binding to FcRn. In mice, the serum half-life of humanized CA645 Fab is 84.2 h. This is a significant extension in comparison with < 1 h for a non-HSA binding CA645 Fab variant. The Fab-HSA structure was used to design a series of mutants with reduced affinity to investigate the correlation between the affinity for albumin and serum half-life. Reduction in the affinity for MSA by 144-fold from 2.2 nM to 316 nM had no effect on serum half-life. Strikingly, despite a reduction in affinity to 62 µM, an extension in serum half-life of 26.4 h was still obtained. CA645 Fab and the CA645 Fab-HSA complex have been deposited in the Protein Data Bank (PDB) with accession codes, 5FUZ and 5FUO, respectively.     

Effect of secondary plant substances on winter wheat resistance to grain aphid

The association between the concentrations of hydroxamic acids, total phenols, and indole alkoloids in winter wheat cultivars with their antibiotic resistance to the grain aphid Sitobion avenae (F.) (Homoptera: Aphididae) was studied. The antibiosis was measured under field conditions using the intrinsic rate of natural increase (r_m). The content of the studied allelochemicals was estimated in flag leaf at the anthesis growth stage. Highly significant negative correlations were found between the r_m values and the concentrations of hydroxamic acids (r=–0.905) and total phenols (r=–0.946), but not with indole alkaloids (r=–0.380). The contribution of these allelochemicals to the resistance of winter wheat to S. avenae is discussed.

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Résumé Les effets combinés de la concentration en substances allélochimiques des feuilles flétries et de la résistance antibiotique aux pucerons des grains ont été étudiés sur 4 cultivars de blé d'hiver, dont 2 modérément résistants: Saga et Grana et 2 sensibles: Emika et Liwilla. L'antibiose a été évaluée dans les conditions de la nature, aux stades d'épiaison et d'anthèse, en utilisant le taux intrinsèque de croissance r_m. La quantification des substances allélochimiques a été effectuée par colorimétrie.Des corrélations négatives hautement significatives ont été trouvées entre les valeurs de R_m et la concentration en acides hydroxamiques (r=–0,905 pour 10 dl, P<0,01) et la teneur totale en phénols (r=–0,946, pour 10 dl, P<0,01). La teneur en alcaloïdes indols était elle aussi corrélée négativement, mais pas significativement avec r_m (r=–0,380, pour 10 dl, P>0,1). La discussion porte sur la contribution de ces substances allélochimiques à la résistance du blé d'hiver à Sitobion avenae.

     

Cold hardiness and overwintering of the grain aphid Sitobion avenae

ABSTRACT.

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

     

Feeding behavior and transmission of barley yellow dwarf virus by Sitobion avenae on oats

Feeding behavior of Sitobion avenae F. (Homoptera: Aphididae) on oats (Avena sativa cv. Clintland 64) was electronically monitored, and waveforms corresponding to salivation, ingestion, and sieve element penetration described.During 90 min plant access, aphids ingested from phloem for 0–43 min (mean: 8.1 min) and non-phloem for 0–60 min (mean: 19 min). Only 65% of the aphids tested made phloem contact within 90 min, contacting phloem after 18–85 min (mean: 32 min). No significant difference was observed in the feeding behavior of aphids carrying barley yellow dwarf virus (BYDV) from that of non-viruliferous aphids.Penetration of a sieve element was a prerequisite for BYDV transmission but did not insure transmission. Penetration of one sieve element resulted in a 65% chance of transmission independent of the duration of phloem contact. The chance of transmission increased with increasing number of sieve element penetrations.Inoculation of oat seedlings with single, viruliferous aphids for 90 min is estimated to cause 54% of the plants to be infected. Also, it is estimated that no transmission can occur with plant access periods shorter than 17 min.

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Zusammenfassung Das Probeverhalten von Sitobion avenae F. (Homoptera: Aphididae) auf Hafer (Sorte Clintland 64) wurden elektronisch verfolgt. Drei Wellenformen (S=Speichelfluss, X-das Eindringen in ein Siebelement, I=Nahrungsaufname) wurden registriert. In histologischen Untersuchungen wurden diese Wellenformen mit der Position der Stechborsten korreliert. Wenn X-Wellen oder eine X-I-Folge registriert wurden, war die Stechborste immer im Phloëm; bei S-Wellen oder bei einer S-I-Folge, war die Stechborste nie im Phloëm.Die Blattläuse wurden auf gesunden, fünf Tage alten Pflanzen während 90 Min beobachtet. 65% der Blattläuse erreichten nach 18–85 Min (Durchschnitt 32 Min) das Phloëm. Innerhalb 90 Min nahmen die Blattläuse während 0–43 Min (Durchschnitt 8.1 Min) Saft aus dem Phloem und während 0–60 Min (Durchschnitt 19 Min) Saft aus dem Mesophyll auf. Keine signifikanten Unterschiede im Probeverhalten wurden bei Blattläusen mit und ohne Barley Yellow Dwarf Virus (BYDV) festgestellt.Blattläuse, die innerhalb 24 Stunden BYDV übermitteln können, wurden für Übertragungsversuche verwendet. Das Probeverhalten dieser Blattläuser wurde manipuliert, und die Leistungsfähigkeit der Übertragung mit einer immunologischen Technik (ELISA) untersucht. Um BYDV zu übertragen mussten die Blattläuse mit einem Siebelement in Kontakt kommen. Nach der Stechborstenpenetration in ein Siebelement wurden 65% der Pflanzen mit BYDV infiziert. Der Prozentsatz infizierter Pflanzen und der Virusiter in den infizierten Pflanzen waren mit der Dauer der Siebelement-penetration (Anzahl von X-Wellen) nicht proportional. Wenn die Blattläuse mit zwei oder drei Siebelementen in Kontakt kamen, wurde der Prozentsatz infizierter Pflanzen signifikant erhöht, während der Virustiter nich verändert wurde. Infektionsprozente niedriger als 100% nach Siebelement-penetration sind möglicherweise das Resultat von Unterschieden in den Siebelementen.Es wird geschätzt dass 50% Infektion eintritt, wenn Pflanzen während ungefähr 83 Min von einer einzelnen infizierten Blattlaus besogen werden. Keine Übertragung von BYDV kann eintreten, wenn die Probezeit weniger als 17 Minuten beträgt.

     

Biology of Aphidius rhopalosiphi, a parasitoid of cereal aphids

Summary Aphidius rhopalosiphi produced 212 offspring on average but in one case 509 deposited eggs were found. Superparasitization occurred but the frequency distribution of parasitoid larvae in aphids differed significantly from random, indicating a certain degree of host discrimination. Average life span of adults was 13.1 days and sex ratio was 1:1. It changed in time among successively produced offspring.Handling time was about 2 sec and was somewhat longer in the fourth instar than in the second. Second and third aphid instars were preferred for oviposition. Functional response was sigmoid and at an aphid density of 100 aphids per cage percentage parasitization decreased.

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Résumé Nous avons examiné quelques aspects des relations entre le parasitoïde Aphidius rhopalosiphi et son hôte Sitobion avenae. La fécondité potentielle à l'émergence (144 ufs) était inférieure à la fécondité réalisée: nombre de pucerons momifiés (212). La plupart des ufs étaient pondus dans la première semaine de la vie imaginale (fig. 1). Le super-parasi-tisme s'est produit dans les conditions expérimentales, mais la distribution des larves (fig. 2) s'écartait souvent de la distribution au hasard, ce qui indiquait une certaine discrimination parmi les hôtes.La longévité moyenne était de 13,1 jours et le maximum de 23 jours. Le taux sexuel (fig. 3) pour l'ensemble de la descendance était 1/1, mais changeait dans le temps. Après le premier jour de ponte, plus de femelles que de mâles étaient obtenues; mais après 6 jours, il n'y avait presque plus que des mâles.Le taux de rencontre des aphides et des parasitoïdes augmentait avec la taille (fig. 4a). Le temps de prospection de l'hôte était en moyenne de 2 secondes, mais dans certains cas il atteignait 10 secondes ou plus. La proportion de rencontres efficaces était plus faible au 4ème stade (fig. 4b). Il n'y avait pas de différence significative dans le nombre de larves de parasitoïdes obtenues par rencontre pendant les stades 1 à 3 des pucerons, mais elle était significativement inférieure au 4ème stade par rapport au second. Les taux globaux de succès (taux de rencontre et nombre de larves formées par rencontre) étaient plus élevés aux 2ème stades des pucerons. La réponse fonctionnelle était sigmoïde (fig. 5).

     

Temporal changes in lectin binding of peri-implantation mouse blastocysts

Mouse blastocysts were exposed to a series of ferritin-conjugated lectins during Day 5 (preadhesive) and Day 6 (adhesive; collected Day 5, 24 hr in vitro) of embryogenesis to determine whether there were any changes in lectin binding characteristics that coincided with the acquisition of adhesiveness. After exposure to lectin, the blastocysts were processed for electron microscopy and lectin binding sites were determined by visualization of ferritin particles with the electron microscope. No binding sites were observed for either Dolichos biflorus agglutinin or soybean agglutinin on blastocysts from either stage examined. Binding sites for Ulex europaeus agglutinin, Con A, and wheat germ agglutinin were seen on blastocysts from both stages without apparent increase or reduction in binding sites from either stage. Ricinus communis agglutinin-I (RCA-I) bound heavily to the surface of Day 5 blastocysts and did not bind at all to $\text{3}\text{12}$ Day 6 blastocysts and did bind, though with apparent diminution, to $\text{9}\text{12}$ Day 6 blastocysts, as compared with the binding observed on Day 5 blastocysts. Peanut agglutinin (PNA) did not bind at all to Day 5 blastocysts but did bind heavily to the surface of Day 6 blastocysts. Both RCA-I and PNA bound to the surface of embryos during Day 5 of delayed implantation, thus indicating that neither the appearance of PNA binding sites on Day 6 blastocysts nor the apparent reduction of RCA-I binding sites on Day 6 blastocysts could be solely implicated in the acquisition of adhesiveness. PNA binding sites were abolished from the surface of Day 6 blastocysts by treatment with Pronase, indicating that the PNA binding molecule was associated with a glycoprotein rather than a glycolipid.