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  • 1
    ISSN: 1615-6102
    Keywords: Whitefly ; Bacteria ; Symbiosis ; Micro-organism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of the mycetocytes and mycetome micro-organisms of the sweetpotato whitefly,Bemisia tabaci Genn. andTrialeurodes vaporariorum West are described. InB. tabaci, two morphologically distinct types of micro-organisms were observed in mycetocytes. The predominant type lacked a distinct cell wall, was pleomorphic in shape with a surrounding vacuole. The second type was a coccoid organism, with inner and outer cell membranes. The coccoid organism was often found in groups of varying number within vacuoles, and in many cases appeared to be undergoing degradation. InT. vaporariorum mycetocytes, pleomorphic and coccoid organisms were found, although the coccoid micro-organism inT. vaporariorum, had a thicker cell wall than the coccoid micro-organism inB. tabaci.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1615-6102
    Keywords: Bacteria ; Bemisia tabaci ; Bemisia argentifolii ; Endosymbionts ; Microorganism ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of the endosymbionts of several populations of whitefly (Homoptera: Aleyrodidae) was examined using transmission electron microscopy. Consistent differences in morphology and relative number of endosymbionts were observed between species and biotypes of whitefly within the Bemisia taxon.Bemisia argentifolii (=B. tabaci B biotype) individuals from Hawaii, Florida, and Arizona contained two morphological types of microorganisms housed within the mycetocyte cells of immature whiteflies. In contrast, individuals from populations ofB. tabaci A biotype from Arizona and Mexico, andB. tabaci Jatropha biotype from Puerto Rico, consistently contained three distinct morphological types of microorganisms within their mycetocytes. Organisms fromB. tabaci A and Jatropha biotypes differed from each other in the relative frequency of each type of microorganism. These observations suggest that different whitefly biotypes may have variable combinations of micro-fauna, with some possibly unique to each group, and furthers the hypothesis that variation in whitefly endosymbionts may be associated with the development of biotypes.
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  • 3
    ISSN: 1570-7458
    Keywords: Insecta ; Bemisia tabaci ; Homoptera ; Aleyrodidae ; spatial variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Susceptibility to acephate, methomyl, and permethrin was determined with laboratory bioassays of field-collected adults from 15 populations of the B biotype of sweetpotato whitefly,Bemisia tabaci (Gennadius) (Homoptera:Aleyrodidae), from Hawaii. Comparisons at the LC50 showed up to 24-fold resistance to acephate, 18-fold resistance to methomyl, and 4-fold resistance to permethrin. Analysis of variance showed significant intra-island variation in susceptibility to each insecticide, but no significant variation among islands. Insecticide use varied from 4 to 103 insecticide sprays per site per season. Acephate and methomyl were used more often than permethrin. The frequency of application and LC50 for each insecticide were positively correlated across sites. These results suggest that local variation in insecticide use was a primary cause of variation in susceptibility. If local insecticide use is a key determinant of resistance, as our results suggest, growers can retard resistance development locally by reducing their own insecticide use.
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  • 4
    ISSN: 1570-7458
    Keywords: hemiptera ; aphididae ; Macrosiphum euphorbiae ; potato aphid ; tomato ; Mi ; Meu1 ; resistance mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of the tomato resistance gene, Meu1, on feeding, longevity, fecundity and developmental rate of the pink biotype of the potato aphid, Macrosiphum euphorbiae (Thomas) (Hemiptera, Aphididae), was determined using nearly isogenic tomato (Lycopersicon esculentum Mill, Solanaceae) lines. Aphid mortality was significantly higher on resistant plants, with 60% of the aphids dying by the 4th day of exposure. By the 10th day, all the aphids on the resistant plants were dead whereas 100% of the aphids on susceptible plants were alive. Meu1-mediated resistance resulted in significantly decreased fecundity with a ten-fold decrease in the net fertility rate (4.5 and 45.7 progeny per aphid on resistant and susceptible tomato, respectively). A qualitative analysis showed that honeydew was produced by aphids on resistant and susceptible plants, suggesting that aphids initiate feeding on both plant types. However, significantly lower quantities of honeydew were present when aphids were caged on resistant plants. There were also significant differences in aphid location on resistant and susceptible leaves. Experiments evaluating behavior in less than 24 h showed that aphids left resistant leaves after relatively short exposure (3–6 h). Aphids transferred from resistant to susceptible tomato at intervals between 3 h and 24 h resumed feeding as evidenced by presence of honeydew. Although the mechanism by which Meu1-mediated resistance operates is not yet known, our data suggest that resistance factors act rapidly after initiation of feeding and that lower fecundity and longevity are related to reduction in aphid feeding.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 47 (1988), S. 115-125 
    ISSN: 1570-7458
    Keywords: probing behavior ; gustatory sensory system ; pear psylla ; Psylla pyricola ; Homoptera ; pear decline vector ; tissue preference
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Les lieux d'insertion des stylets sur la surface de la feuille et les types cellulaires consommés par les larves et les adultes de Psylla pyricola Foerster ont été précisés par étude histologique et par enregistrement électronique du comportement de piqûre et d'alimentation. Ni les larves, ni les adultes n'ont absorbé de préférence le phloème de Pyrus communis de la variété ‘Bartlett’. Nous avons constaté que le psylle du poirier ingère le contenu de tous les types cellulaires, mais que le xylème, le phloème et autre cellules des faisceaux libéro-ligneux étaient préferés aux tissus non vasculaires. La discussion a porte sur les méchanismes sensoriels éventuellement responsables de la sélection des lieux d'insertion des stylets à la surface de la feuille et l'acceptation des différents types cellulaires lors de l'ingestion.
    Notes: Abstract Stylet insertion sites on the leaf surface and leaf cell types fed upon by nymphs and adults of the pear psylla, Psylla pyricola Foerster (Homoptera: Psyllidae) were identified using histological techniques and electronic monitoring of probing and feeding activities. Neither the nymphs nor the adult ingested predominantly from the phloem of Pyrus communis cv. ‘Bartlett’. We showed that the pear psylla ingests from all leaf cell types, but that xylem, phloem and bundle sheath cells are more acceptable for ingestion than non-vascular tissues. The possible sensory mechanisms underlying selection of stylet insertion sites on the leaf surface and acceptance of various cell types for ingestion are discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Phytopathology 30 (1992), S. 315-348 
    ISSN: 0066-4286
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Biology
    Type of Medium: Electronic Resource
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