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  • 1
    ISSN: 1573-5117
    Keywords: plankton ; diet change ; vertical migration ; crowding ; light intensity ; pond ; water chemistry ; nutrient changes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a flooded Fenland brickpit 3 metres deep a 24-hr study (supplemented by other observations in the field and in the laboratory) revealed marked changes with depth and time in oxygen concentration, pH, total carbon dioxide, ammonium, oxidised nitrogen, phosphate and silica; as well as changes in the rate of cell-division and the vertical distribution of phytoplankton (Dinobryon and Peridinium), and the feeding and vertical movement of zooplankton (copepods, Bosmina, Ceriodaphnia, Polyarthra and Keratella). Directional trapping of zooplankton revealed relationships between population density and the intensity of locomotory activity (a relationship subsequently supported by laboratory experiments), and between the rate of change of light intensity and the direction of swimming. Significant temporal segregation of the occupancy of a given level by zooplankters implies interspecific competition. Transient peaks in the concentrations of some nutrients near the surface are tentatively attributed to nutrient release by zooplankters that have fed at depth. Small-scale temporal and spatial heterogeneity of the type described here may help to explain the ‘paradox of the plankton’. These marked diel changes in water chemistry suggest that conclusions based on the analysis of single water samples should be viewed with caution.[/p]
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-8248
    Keywords: Biological control ; Epiblema strenuana ; Tortricidae ; Parthenium hysterophorus ; Compositae ; Mexico ; Lutte biologique ; Epiblema strenuana ; Tortricidae ; Parthenium hysterophorus ; Compositae ; Mexique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Resumen Se encontró que el tortricidoEpiblema strenuana, que atacaAmbrosia spp. en la mayor parte de Norteamérica, utiliza aParthenium hysterophorus como hospedera principal en el norte de México. Las larvas producen agallas en el tallo y en las yemas, y pueden ocasionar una considerable inhibición en el crecimiento al atacar plantas jóvenes. En pruebas se encontró que el insecto tiene un rango restringido en hospederas y que no es capaz de dañar ninguna planta de importancia económica dentro de la familia de las compuestas. Se ha autorizado su liberación en Australia para probar su eficacia como agente de control biológico contraP. hysterophorus.
    Abstract: Résumé La tordeuseEpiblema strenuana, qui attaque les espèces du genreAmbrosia dans la majeure partie de l'Amérique du nord, utiliseParthenium hysterophorus [Compositae] comme principal hôte dans la région nord du Mexique. Les larves produisent des galles dans les tiges et les bourgeons, qui peuvent arrêter la croissance quand les jeunes plantes sont attaquées. Les essais ont montré la gamme limitée d'hôtes, dont sont exclues toutes composées d'importance économique, que possède la tordeuse. Son introduction en Australie comme agent de lutte biologique contreP. hysterophorus a été approuvée.
    Notes: Abstract The tortricid mothEpiblema strenuana (Walker), which attacksAmbrosia spp. over most of North America, is shown to have the annual weedParthenium hysterophorus L. [Compositae] as its main host in northern Mexico. The larvae produce galls in the stems and growing-points which can considerably stunt growth when young plants are attacked. In tests it was shown to have a restricted host-range and not to damage any composite of economic importance. Its release in Australia for trial as a biological control agent againstP. hysterophorus has been approved.
    Type of Medium: Electronic Resource
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