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Earth is now experiencing declines in insect abundance and diversity unparalleled in human history. The drivers underlying those declines are many, complex, and incompletely known. Here, using a natural experiment, we report the first test of the hypothesis that forest defoliation by an invasive outbreak insect compromises the fitness of a native insect via damage‐induced increases in toxicity of the forest canopy. We demonstrate that defoliation by the invasive spongy moth (Lymantria dispar) elicits an average 8.4‐fold increase in foliar defense expression among aspen (Populus tremuloides) genotypes. In turn, elevated defense dramatically reduces survivorship, feeding, and growth of a charismatic mega moth (Anthereae polyphemus). This work suggests that changes to the phytochemical landscape of forests, mediated by invasive outbreak insects, are likely to negatively impact native insects, with potential repercussions for community diversity and ecosystem function across expansive scales. [ABSTRACT FROM AUTHOR]

Leucoptera sinuella (Reutti) (Lepidoptera: Lyonetiidae) is a leaf miner specialist on Salicaceae recently introduced to Chile and Argentina, where it is causing economic damage to poplar plantations. We report a field survey in a poplar nursery naturally infested showing that regardless of the poplar hybrid taxon, high variability in resistance was observed among clones within families for oviposition and leaf-mining damage. A group of susceptible and resistant hybrid poplar clones was then selected for a laboratory evaluation of oviposition (antixenosis) and leaf-mining damage (antibiosis) on potted, rooted shoot cuttings. The concentration of condensed tannins (CTs) and salicinoid phenolic glucosides (SPGs) of the leaves of the selected clones from the laboratory study was also measured. Total oviposited eggs were positively correlated with leaf area, with the lowest oviposition on TMxT 11372 clone. The lowest percentage of mined leaf area was obtained for clones TMxT 11372, TMxT 11463, and TDxD 17574, but surprisingly no correlation between the percentage of mined leaf area and concentration of CTs and SPGs was found. Resistant poplar hybrids of our study could be suitable for breeding programs aimed for L. sinuella integrated pest management. [ABSTRACT FROM AUTHOR]

Diseases can markedly alter the ecological and economic value of poplars. To better understand poplar-pathogen interactions, we investigated the independent and interactive effects of tree genotype, soil nutrient limitation, and interspecific competition on incidence of powdery mildew (caused by the fungal obligate pathogen Erysiphe adunca (Wallr.) Fr., 1829) in a foundation tree species, trembling aspen (Populus tremuloides Michx.). We established a common garden of potted aspen saplings, incorporating five tree genotypes, two levels of soil nutrients (low and high), and two levels of competition (with and without grass). We then surveyed natural incidence of powdery mildew and aspen vigor (i.e., growth). Incidence of powdery mildew varied among aspen genotypes, and variance in incidence shifted among environments in which the trees were grown. Added soil nutrients increased powdery mildew incidence on aspen, whereas grass competition had the opposite effect. Interestingly, grass competition either enhanced or dampened the variance in incidence of powdery mildew among tree genotypes, depending on soil nutrient levels. In addition, powdery mildew incidence was positively related to tree vigor. Our findings reveal strong genetic, environmental, and geneticxenvironmental effects of disease on a foundation tree species and that particular environments can either enhance or diminish variation in responses among tree genotypes. Key words: Populus, nutrients, competition, fungal pathogen, genetic variation. Les maladies peuvent manifestement modifier la valeur ecologique et economique des peupliers. Pour mieux comprendre les interactions entre les peupliers et les pathogenes, nous avons etudie les effets independants et interactifs de trois genotypes, de la limitation des nutriments dans le sol et de la competition interspecifique sur l'incidence du blanc des feuilles cause par le champignon pathogene Erysiphe adunca (Wallr.) Fr., 1829, un parasite obligatoire, sur une espece d'arbre fondatrice, le peuplier faux-tremble (Populus tremuloides Michx.). Nous avons etabli un jardin commun de gaules de peuplier en pot, compose de cinq genotypes, deux niveaux de nutriments dans le sol (faible et eleve) et deux niveaux de competition (avec et sans plante herbacee). Nous avons ensuite fait un releve de l'incidence naturelle du blanc des feuilles et de la vigueur du peuplier (c.-a-d. la croissance). L'incidence du blanc des feuilles variait selon le genotype du peuplier et la variance de l'incidence changeait selon le milieu dans lequel les arbres etaient cultives. L'ajout de nutriment dans le sol a augmente l'incidence du blanc des feuilles sur le peuplier tandis que la competition d'une plante herbacee a eu l'effet contraire. Il est interessant de noter que la competition d'une plante herbacee a soit augmente, soit diminue la variance de l'incidence du blanc des feuilles parmi les genotypes dependemment du niveau de nutriments dans le sol. De plus, l'incidence du blanc des feuilles etait positivement reliee a la vigueur des arbres. Nos resultats revelent que la genetique, l'environnement et l'interaction entre les deux ont une forte influence sur la facon dont le blanc des feuilles affecte une espece d'arbre fondatrice et que certains milieux peuvent soit amplifier, soit reduire la variation des reactions de differents genotypes d'arbre. [Traduit par la Redaction] Mots-cles : Populus, nutriments, competition, champignon pathogene, variation genetique., Introduction Poplars (Populus) are widely distributed and genetically diverse tree species (Mitton and Grant 1996; Slavov and Zhelev 2010) with considerable ecological and economic importance. In natural and managed environments, [...]

Background and Aims At the population level, genetic diversity is a key determinant of a tree species' capacity to cope with stress. However, little is known about the relative importance of the different components of genetic diversity for tree stress responses. We compared how two sources of genetic diversity, genotype and cytotype (i.e. differences in ploidy levels), influence growth, phytochemical and physiological traits of Populus tremuloides in the presence and absence of environmental stress. Methods In a series of field studies, we first assessed variation in traits across diploid and triploid aspen genotypes from Utah and Wisconsin under non-stressed conditions. In two follow-up experiments, we exposed diploid and triploid aspen genotypes from Wisconsin to individual and interactive drought stress and defoliation treatments and quantified trait variations under stress. Key Results We found that (1) tree growth and associated traits did not differ significantly between ploidy levels under non-stressed conditions. Instead, variation in tree growth and most other traits was driven by genotypic and population differences. (2) Genotypic differences were critical for explaining variation of most functional traits and their responses to stress. (3) Ploidy level played a subtle role in shaping traits and trait stress responses, as its influence was typically obscured by genotypic differences. (4) As an exception to the third conclusion, we showed that triploid trees expressed 17 % higher foliar defence (tremulacin) levels, 11 % higher photosynthesis levels and 23 % higher rubisco activity under well-watered conditions. Moreover, triploid trees displayed greater drought resilience than diploids as they produced 35 % more new tissue than diploids when recovering from drought stress. Conclusion Although ploidy level can strongly influence the ecology of tree species, those effects may be relatively small in contrast to the effects of genotypic variation in highly diverse species. [ABSTRACT FROM AUTHOR]