The woolly poplar aphid, Phloeomyzus passerinii (Signoret) (Hemiptera: Aphididae), is a major pest of poplar plantations in the Mediterranean basin and the Near East. Aphids colonize poplar trunks ...and feed upon the cortical parenchyma. Despite the economic importance of poplar, little is known about the mechanisms involved in poplar resistance to this pest. However, Populus x canadensis Moench genotypes show various levels of resistance to P. passerinii. This study has investigated the type of poplar resistance (antibiosis or antixenosis) by assessing aphid settlement, physiology (survival, development, and reproduction), and stylet penetration behavior (electrical penetration graph) on three P. x canadensis genotypes; ‘I214’ (susceptible), ‘Brenta’ (resistant), and ‘I45/51’ (intermediate). Because settlement was reduced, the highly resistant genotype Brenta exhibited surface antixenosis. In addition, nymphal survival was null on Brenta, and twice less adult aphid initiated a sustained intracellular phase in the cortical parenchyma of that genotype compared with the other two genotypes. Thus, Brenta also showed parenchyma-located antixenosis coupled with antibiosis characteristic. In contrast, P. passerinii had no difficulty to initiate a sustained ingestion in the cortical parenchyma of the intermediate genotype I45/51, but decreased fecundity and lower intrinsic rate of natural increase were clear expressions of antibiosis.
1 High intraspecific competition is known to occur during Ips typographus outbreaks, and is thought to be the main factor regulating epidemic populations by affecting beetle population productivity. ...However, little is known about the consequences of intraspecific competition on population quality during outbreaks, although it could have consequences on beetle population dynamics.
2 Ips typographus morphological variations among localities, years and beetle population levels were investigated in 10 Norway spruce (Picea abies) stands having various beetle damage intensities. Beetle size and shape estimators based on wing length, and using isometric size and log‐shape ratios, were employed. Field‐caught beetles were compared with beetles emerging from controlled breeding at different densities, performed in the laboratory. Beetles from this colony were also used to check the influence of breeding densities on the size estimator.
3 Size variations occurred among localities and years and were consistent with the epidemic or latent status of the beetle populations. Controlled breeding confirmed the negative effect of beetle densities encountered in the field on offspring size. Two hypotheses are formulated to explain this increase of intraspecific competition during an outbreak, but our data support the effect of host quality change between latent and epidemic populations.
4 Shape variations also occurred among localities but were unrelated to beetle population levels. No groups consistent with a geographical structure were found, suggesting low genetic variation for I. typographus populations in France.
Aim
Climate is a major driver of large‐scale variability in biodiversity, as a likely result of more intense biotic interactions under warmer conditions. This idea fuelled decades of research on ...plant‐herbivore interactions, but much less is known about higher‐level trophic interactions. We addressed this research gap by characterizing both bird diversity and avian predation along a climatic gradient at the European scale.
Location
Europe.
Taxon
Insectivorous birds and pedunculate oaks.
Methods
We deployed plasticine caterpillars in 138 oak trees in 47 sites along a 19° latitudinal gradient in Europe to quantify bird insectivory through predation attempts. In addition, we used passive acoustic monitoring to (i) characterize the acoustic diversity of surrounding soundscapes; (ii) approximate bird abundance and activity through passive acoustic recordings; and (iii) infer both taxonomic and functional diversity of insectivorous birds from recordings.
Results
The functional diversity of insectivorous birds increased with warmer climates. Bird predation increased with forest cover and bird acoustic activity but decreased with mean annual temperature and functional richness of insectivorous birds. Contrary to our predictions, climatic clines in bird predation attempts were not directly mediated by changes in insectivorous bird diversity or acoustic activity, but climate and habitat still had independent effects on predation attempts.
Main Conclusions
Our study supports the hypothesis of an increase in the diversity of insectivorous birds towards warmer climates but refutes the idea that an increase in diversity would lead to more predation and advocates for better accounting for activity and abundance of insectivorous birds when studying the large‐scale variation in insect‐tree interactions.
Résumé
Objectif
Le climat est l'un des principaux facteur structurant de la variabilité à grande échelle de la biodiversité, possiblement en raison d'interactions biotiques plus intenses dans des conditions de température plus élevées. Cette idée a alimenté des décennies de recherche sur les interactions plantes‐herbivores, mais on en sait beaucoup moins sur les interactions impliquant les niveaux trophiques supérieurs. Nous avons comblé cette lacune en caractérisant à la fois la diversité des oiseaux et leur activité de prédation le long d'un gradient climatique à l'échelle européenne.
Localisation
Europe.
Taxon
Oiseaux insectivores et chênes pédonculés.
Méthodes
Nous avons déployé des leurres en pâte à modeler mimant des chenilles sur 138 chênes dans 47 sites le long d'un gradient latitudinal de 19° en Europe pour quantifier l'insectivorie avienne par le biais de tentatives de prédation. De plus, nous avons utilisé la surveillance acoustique passive pour (i) caractériser la diversité acoustique des paysages sonores environnants; (ii) estimer l'abondance et l'activité des oiseaux à travers des enregistrements acoustiques passifs et (iii) déduire à la fois la diversité taxonomique et fonctionnelle des oiseaux insectivores à partir des enregistrements.
Résultats
Nous avons montré une augmentation de la diversité fonctionnelle des oiseaux insectivores avec la température moyenne. La prédation avienne augmentait avec la couverture forestière et l'activité acoustique des oiseaux, mais diminuait avec la température annuelle moyenne et la richesse fonctionnelle des oiseaux insectivores. Contrairement à nos prédictions, la variation de la diversité des oiseaux n'était pas le lien mécaniste entre le climat et la variation des tentatives de prédation sur les leurres, laquelle était directement influencée par le climat et la couverture forestière.
Conclusions Principales
Notre étude confirme l'hypothèse d'une augmentation de la diversité des oiseaux insectivores vers des climats plus chauds, mais ne corrobore pas l'idée qu'une augmentation de la diversité conduirait à davantage de predation. Elle plaide en faveur d'une meilleure prise en compte de l'activité et de l'abondance des oiseaux insectivores lors de l'étude de la variation à grande échelle des interactions entre insectes et arbres.
Climate change and silvicultural practices promoted the emergence of a novel pest of poplar stands POINTEAU, Sophie; Robinet, Christelle; Bankhead-Dronnet, Stéphanie ...
The International Forestry Review. Sustaining Forests, Sustaining people: The role of research . (16(5))2014; 24. IUFRO World Congress-The International Forestry Review. Sustaining Forests, Sustaining people: The role of research , Salt Lake City, USA, 2014-10-05-2014-10-11, 489,
2014
Conference Proceeding
Climate change and silvicultural practices promoted the emergence of a novel pest of poplar stands POINTEAU, Sophie; Robinet, Christelle; Bankhead-Dronnet, Stéphanie ...
The International Forestry Review. Sustaining Forests, Sustaining people: The role of research . (16(5))2014; 24. IUFRO World Congress-The International Forestry Review. Sustaining Forests, Sustaining people: The role of research , Salt Lake City, USA, 2014-10-05-2014-10-11, 489,
2014
Conference Proceeding
•We study how poplar genotype mediates water deficit effects on a gall-inducing aphid.•Three irrigation levels were applied to a susceptible and a resistant host genotype.•For both genotypes, water ...deficit affected plant growth and gall anatomy.•The effect of water deficit on aphid performance differed according to host genotype.•The medium irrigation level favored aphid development on the resistant host.
Successful plant manipulation by herbivores requires a reconfiguration of the primary and secondary metabolisms of the host-plant. Water deficit is generally predicted to negatively affect the development of gall-inducing insects, by impairing their ability to remodel the primary metabolism of their host. We assessed whether host genotype could modulate water deficit effects on a gall-inducing aphid, Phloeomyzus passerinii, developing on poplars, which are known to be among the most susceptible trees to water deficit. Stem-cuttings of two poplar genotypes, with a different resistance level to P. passerinii, were grown under three irrigation treatments, and subsequently infested with the same aphid clone. Plant growth parameters and aphid colonies development were recorded, and the development and organization of the pseudogall induced by the aphid was observed using histological investigations. The three irrigation treatments resulted in three levels of water deficit. Mean predawn leaf water potential reached −0.10, −0.49 and −0.75MPa in the optimal, intermediate and low irrigation treatments respectively. In both genotypes, growth, architecture and photosynthesis were similarly affected. The severe water deficit reduced the development of aphids on both genotypes, which is in agreement with the general prediction for gall-inducing insects. Nonetheless, while the intermediate water deficit did not affect the development of aphids on the susceptible genotype, it enhanced their development on the resistant one. This latter observation contradicts the prediction for gall-inducing insects, but is in agreement with the plant stress hypothesis for sucking insects. The size of the pseudogall induced by the aphids in the bark of their host progressively diminished when water deficit increased. Lignification, believed to be an important component of poplar resistance to P. passerinii, also progressively decreased with water deficit. The involvement of physiological and architecture modifications due to water deficit on the development of aphids is discussed. The results demonstrate that host genotype can modulate water deficit effects on the development of a galling aphid, thereby compromising predictions on the outcome of droughts on stand resistance to plant-manipulating herbivores.
KEY MESSAGE : Phloeomyzus passerinii can induce a pseudogall within the bark of susceptible poplar genotypes, while in resistant genotypes the induction seems to be impeded by lignification ...processes. Phloeomyzus passerinii is a major pest of poplar stands in Europe, North Africa and the Near East. This aphid feeds in the cortical parenchyma of different poplar species and hybrids, and can affect their growth and survival through unknown mechanisms. In some genotypes, however, resistance prevents either the settlement or the development of aphid colonies. For a better understanding of tree reactions to aphid probing, we compared the anatomical and biochemical modifications undergone within the bark of stem cuttings, after different delays of either aphid colonization or mechanical wounding. To assess how resistance may modulate tree reactions, the comparison was performed using three poplar genotypes exhibiting different resistance levels. In these three genotypes, mechanical wounding induced a similar, localized, wound periderm. In contrast, aphid colonization triggered more extended reactions, which differed among genotypes. In the susceptible genotype, aphids induced a reaction tissue, characterized after a month by thin-walled hypertrophied cells and a depletion of soluble phenolic compounds and starch. Anatomical features of this reaction tissue suggest that the aphid initiates a pseudogall in the cortical tissues of its susceptible host. In the resistant genotypes, however, the differentiation of the reaction tissue was totally or partially inhibited, probably because of extended lignification processes. The implications of a pseudogall induction on susceptible hosts’ physiology, and the impact of lignification on aphid development and behavior, are discussed.
Le puceron lanigère du peuplier. Phloeomyzus passerinii est un ravageur important des peupleraies du sud de l'Europe, du Proche-Orient et d'Afrique du Nord. Après une insertion de ses stylets, à la ...fois intercellulaire et intracellulaire, il se nourrit exclusivement dans le parenchyme cortical du tronc des peupliers. Durant les pullulations, ce puceron Cause des nécroses corticales étendues et un dessèchement des rameaux, pouvant conduire à la mort de l'arbre. Nous avons comparé la réaction corticale après blessure mécanique et après piqure du puceron entre deux génotypes hybrides Populus x canadensis avec des niveaux de résistance contrastés ('I214' qui est sensible et 'I45/51' qui affecte les paramètres démographiques du puceron). Chaque semaine durant un mois, nous avons réalisé des coupes histologiques autour des zones d'insertion des stylets et des blessures mécaniques pour comparer les modifications anatomiques et biochimiques des tissus de l'écorce. Les blessures mécanique ont induit des péridermes de blessures très localisés alors que l'alimentation du puceron a entraîné des réactions élendues, présentant des similarités avec un bourrelet cicatriciel, mais avec également des cellules hypertrophiées à parois minces, une localisation particulière des dépôts pariétaux de lignine et des accumulations périphériques de tanins et flavanols. Les dépôts de lignine étaient plus étendus et importants chez le génotype résistant. Notre hypothèse est que P. passerinzrii, aveC son mode destructif de pénétration des tissus de son hôte, déclenche les mécanismes de défense du peuplier, puis les manipule pour induire la formation d'une pseudogalle.
Le puceron lanigère du peuplier. Phloeomyzus passerinii est un ravageur important des peupleraies du sud de l'Europe, du Proche-Orient et d'Afrique du Nord. Après une insertion de ses stylets, à la ...fois intercellulaire et intracellulaire, il se nourrit exclusivement dans le parenchyme cortical du tronc des peupliers. Durant les pullulations, ce puceron Cause des nécroses corticales étendues et un dessèchement des rameaux, pouvant conduire à la mort de l'arbre. Nous avons comparé la réaction corticale après blessure mécanique et après piqure du puceron entre deux génotypes hybrides Populus x canadensis avec des niveaux de résistance contrastés ('I214' qui est sensible et 'I45/51' qui affecte les paramètres démographiques du puceron). Chaque semaine durant un mois, nous avons réalisé des coupes histologiques autour des zones d'insertion des stylets et des blessures mécaniques pour comparer les modifications anatomiques et biochimiques des tissus de l'écorce. Les blessures mécanique ont induit des péridermes de blessures très localisés alors que l'alimentation du puceron a entraîné des réactions élendues, présentant des similarités avec un bourrelet cicatriciel, mais avec également des cellules hypertrophiées à parois minces, une localisation particulière des dépôts pariétaux de lignine et des accumulations périphériques de tanins et flavanols. Les dépôts de lignine étaient plus étendus et importants chez le génotype résistant. Notre hypothèse est que P. passerinzrii, aveC son mode destructif de pénétration des tissus de son hôte, déclenche les mécanismes de défense du peuplier, puis les manipule pour induire la formation d'une pseudogalle.
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