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  • 1
    Electronic Resource
    Electronic Resource
    Multiple effects of precipitation onSalix lasiolepis and populations of the stem-galling sawfly,Euura lasiolepis (1986)
    Springer
    Ecological research 1 (1986), S. 1-14 
    Details
    ISSN: 1440-1703
    Keywords: Euura lasiolepis ; Precipitation ; Salix lasiolepis ; Survivorship ; Water experiment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Relatively low winter precipitation (e.g., 18–28 cm from October to May compared to 45 to 65 cm) caused reduced growth of the arroyo willow,Salix lasiolepis, with number of shoots per stem initiated and shoot length reduced. Resources were reduced for the stem-galling sawfly,Euura lasiolepis, which declined in numbers after the relatively dry winter of 1980–81. Sawfly phenology was advanced relative to willow phenology in the 1981 generation, causing an additional reduction in resource availability. These direct effects of precipitation on the sawfly were increased by indirect effects on survivorship of the 1981 generation. Egg death in galls increased on water-stressed willow plants, forming the major mortality in the generation. This resulted in very low survival in the generation and an even lower population in the 1982 generation, even though resources recovered after high precipitation during the 1981–82 winter (46.7 cm). An experiment using high, medium, and low water treatments on potted willow plants demonstrated that the effects on willows and sawflies could be reproduced using only water as a variable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02361200
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  • 2
    Electronic Resource
    Electronic Resource
    Size and shape analysis of mineral resources in arroyo willow and their relation to sawfly densities (1991)
    Springer
    Ecological research 6 (1991), S. 317-331 
    Details
    ISSN: 1440-1703
    Keywords: Foliar mineral nutrients ; Insect-plant interactions ; Salix lasiolepis ; Sawflies ; Size and shape analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The association between host-plant mineral nutrients and insect herbivory is complex, idiosyncratic, and dynamic. Because of this we employed an unusual statistical method to evaluate the relationship between tenthredinid sawfly herbivory and concentrations of foliar nutrients in arroyo willow,Salix lasiolepis. We discovered that among 20 willow clones and between two years arroyo willow varied in the size (absolute concentrations) and shape (relative concentrations) of five mineral nutrients (Ca, Mg, N, P, and K). Similarly, the densities of five sawfly species varied in size and shape among clones and between years. In 1984, relative densities, or shape, of the sawfly community was associated with relative concentrations, or shape, of foliar nutrients in 20 willow clones. In contrast, in 1985 absolute densities, or size, was associated with absolute concentrations, or size, of foliar nutrients. This shift from a shape to a size association between herbivory and foliar mineral nutrients may reflect the large difference in winter precipitation and sawfly densities between years: precipitation and sawfly densities were much greater in 1985 than in 1984.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02347131
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  • 3
    Electronic Resource
    Electronic Resource
    Testing a new hypothesis: plant vigor and phylloxera distribution on wild grape in Arizona (1990)
    Springer
    Oecologia 84 (1990), S. 1-8 
    Details
    ISSN: 1432-1939
    Keywords: Grape phylloxera ; Shoot length ; Plant vigor ; Leat galls ; Distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Longer, meaning more vigorous, shoots of a wild grape clone (Vitis arizonica) were more susceptible to attack by second and third generations of leaf-galling grape phylloxera,Daktulopsphaira vitifoliae, as the growing season progressed. Although there was no significant difference in mean shoot length between attacked and unattacked shoots within a clone at the beginning of shoot elongation, attacked shoots were significantly longer than unattacked shoots when elongation had ceased (P〈0.01). Also, long attacked shoots had a significantly greater population of phylloxera galls than short attacked shoots (P〈0.01) as the season progressed. The phylloxera population on long shoots increased rapidly while the population on short shoots remained the same. Longer shoots also produced significantly more axillary shoots than shorter shoots as the season progressed (P〈0.001), and the number of axillary shoots accounted for 66 percent of the variance in number of attacked leaves on a shoot. Experimental evidence showed that there was a significantly greater percentage of available leaves attacked on long shoots than on short shoots (P〈0.05) and the leaves on long shoots generally had a greater number of galls per leaf. The relationship between shoot length and probability of attack was also tested by comparing shoots lengths of 10 attacked clones and 10 unattacked clones at a second location. Mean shoot lengths of attacked clones were significantly longer than mean shoot lengths of unattacked clones (P〈0.05), and mean shoot lengths of attacked shoots within a clone were significantly longer than unattacked shoots (P〈0.001). Longer shoot length accounted for 81 percent of the variance in probability of attack. The reason for this pattern of attack was that long shoots produced newly expanding leaves over a longer time during the growing season and multivoltine phylloxera require undifferentiated tissue to initiate gall formation. Patterns of attack within a shoot were characterized by an uneven distribution of galls among leaves. This was due to development time between generations and the current availability of undifferentiated tissue at times of colonization. This study supports the hypothesis that some herbivore species are favored more by vigorous plants than by stressed plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665587
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  • 4
    Electronic Resource
    Electronic Resource
    Nonequilibrial community structure of sawflies on arroyo willow (1991)
    Springer
    Oecologia 85 (1991), S. 483-491 
    Details
    ISSN: 1432-1939
    Keywords: Arroyo willow ; Nonequilibrium community structure ; Plant-insect interactions ; Sawfly herbivores ; Size and shape analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We use Wiens' (1984) nonequilibrium-equilibrium continuum concept to evaluate aspects of community structure for sawfly herbivores (Hymenoptera: Tenthredinidae) that attack arroyo willow, Salix lasiolepis. The sawfly community on arroyo willow shares many characteristics of nonequilibrium communities: unsaturation, biotic decoupling, lack of density dependence, and loose emergent patterns. Species abundances exhibit highly significant differences among clones (P〈0.001) and among years (P〈0.001) and exhibit significant and complex clone-by-year interactions both for absolute and relative abundances. Organizing forces, such as interspecific competition and regulation by natural enemies, are largely absent from the arroyo willow system. Sawfly densities exhibit significant positive covariation among willow clones and appear to be affected by largely stochastic abiotic forces, primarily winter precipitation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323759
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  • 5
    Electronic Resource
    Electronic Resource
    Some consequences for a parasitic herbivore, the milkweed longhorn beetle, Tetraopes tetrophthalmus, of a host-plant shift from Asdepias syriaca to A. verticillata (1976)
    Springer
    Oecologia 25 (1976), S. 331-340 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The impact of differences in host plants on individuals and populations of insect herbivores was investigated using the milkweed longhorn beetle, Tetraopes tetrophthalmus (Forster), larvae of which feed parasitically on host rhizomes. One host, Asclepias syriaca L., was larger in stem and rhizome diameter and grew in cooler soil than the other host, A. verticillata L. The major effects on beetles were retarded phenology at the cooler site and reduced size on the smaller host. Reduced size of beetles was correlated with several important individual attributes: reduced length of life, number of ovarioles, egg size, and a reduced probability of mating with large beetles. The population consequences of these characteristics, largely inferred from these observations, were little or no outbreeding in the small population on A. verticillata.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00345606
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  • 6
    Electronic Resource
    Electronic Resource
    Growth of coyote willow and the attack and survival of a mid-rib galling sawfly, Euura sp. (1996)
    Springer
    Oecologia 108 (1996), S. 714-722 
    Details
    ISSN: 1432-1939
    Keywords: Plant/insect interactions ; Host plant variation ; Oviposition behavior ; Euura ; Salix exigua
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We studied the relationship between variation in age and shoot characteristics of the host plant Salix exigua Nuttall (coyote or sandbar willow) and the attack and survival of Euura sp. (an unnamed leaf-midrib galling sawfly). Variation in shoot characteristics resulted from reduced growth as willow ramets aged. Mean shoot length per ramet and mean longest leaf length per shoot decreased by 95% and 50% respectively between 1- and 9-year-old willow ramets. All measured shoot characteristics-shoot length, longest leaf length, number of leaves per shoot, and mean internode length-were significantly negatively correlated with ramet age (r 2 ranged from −0.23 to −0.41). Correlations between shoot characteristics were highly positive, indicating that plants also grew in a strongly integrated fashion (r 2 ranged from 0.54 to 0.85). Four hypotheses were examined to explain sawfly attack patterns. The host-plant hypothesis was supported in explaining enhanced larval sawfly survival through reduced plant resistance. As willow ramets aged, the probability of Euura sp. attack decreased over 10-fold, from 0.315 on 1-year-old ramets to 0.024 on 2- to 9-year-old ramets. As shoot length increased, the probability of sawfly attack increased over 100-fold, from 0.007 on shoots 〈100 mm, to 0.800 on shoots in the 1001–1100 mm shoot length class. These attack patterns occurred even though 1-year-old ramets and shoots 〉500 mm each represented less than 2% of the total shoots available for oviposition. Host plant induced mortality of the egg/early instar stage decreased by 50% on longer leaves and was the most important factor determining survival differences between vigorous and non-vigorous hosts. Sawfly attack was not determined by the resource distribution hypothesis. Although shoots 〈200 mm contained 82% of the total leaves available, they contained only 43% of the galls initiated. The attack pattern also was not explained by the gall volume hypothesis. Although gall volume increased on longer shoots, there was no significant variation in mid or late instar mortality over shoot length, as would be expected if food resources within smaller galls were limited. The natural enemy attack hypothesis could not explain the pattern of oviposition since predation was greater on longer shoots and leaves. In addition, larval survival was related to oviposition behavior. Due to a 69% reduction in late instar death and an 83% reduction in parasitism, survival of progeny in galls initiated close to the petiole base was 2.8 times greater than in galls initiated near the leaf tip. A 75% reduction in gall volume over this range of gall positions may account for the observed increases in late instar mortality and parasitism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329047
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  • 7
    Electronic Resource
    Electronic Resource
    Biogeographical gradients in galling species richness (1988)
    Springer
    Oecologia 76 (1988), S. 161-167 
    Details
    ISSN: 1432-1939
    Keywords: Adaptation ; Altitudinal gradients ; Herbivores ; Insect galls ; Species richness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Five hypotheses were invoked to account for variation in galling species number per location on plants of different structural complexity, namely herbs, shrubs, and trees, both in Brazil and USA. The hypotheses were: 1) the altitudinal/latitudinal gradient hypothesis; 2) the harsh environment hypothesis; 3) the plant species richness hypothesis; 4) the host plant area hypothesis; 5) the plant structural complexity hypothesis. The altitudinal and the harsh environment hypotheses were correlated and supported with sample data in both localities, with increasing gall species number as altitude/latitude declined and as sites became hotter and drier. The two hypotheses were separated by studying riparian sites and dry hillside sites at the same elevation in Arizona. Galling species frequency was higher in dry sites than in riparian sites, supporting the harsh environment hypothesis. Of the five hypotheses tested only the harsh environment hypothesis predicted that galling insect species number should vary in response to environmental variables such as moisture and temperature. Temperate shrubs supported more galling species than did other plant types, both in dry and mesic sites. The overall difference between galling species richness for tropical and temperate latitudes was not statistically significant. Free-feeding insect herbivore species exhibited the opposite pattern of species richness to gallers, being more speciose in riparian sites. The present study corroborates the hypothesis that the gall forming habit is an adaptation to harsh or stressful environments, and we describe for the first time broad scale geographical patterns in galling insect species richness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379948
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  • 8
    Electronic Resource
    Electronic Resource
    The adaptive significance of insect gall distribution: survivorship of species in xeric and mesic habitats (1992)
    Springer
    Oecologia 90 (1992), S. 14-20 
    Details
    ISSN: 1432-1939
    Keywords: Adaptations ; Habitat selection ; Herbivore survivorship ; Insect distribution ; Insect galls
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We studied the relationship between habitat moisture and gall-forming insect populations. Population sizes for most galling taxa were significantly larger in xeric habitats compared with mesic habitats. Our results indicate that the differential abundance of galling insects in these habitats is due primarily to differential mortality and survivorship. Mortality factors acting upon eight insect galling species (belonging to eight genera and four families) were measured on six species (five genera and five families) of host plants. Survival was significantly higher for galling populations inhabiting xeric habitats compared with mesic habitats. Parasitism was higher in mesic habitats in seven of eight habitats and fungus-induced diseases were higher in five of seven habitats. Mortality due to predation and other (unknown) factors showed no clear trends. Overall, there was a tendency towards lower mortality and consequently higher survival for populations inhabiting xeric habitats. We hypothesize that reduced mortality caused by natural enemies and endophytic fungi has contributed to the speciation and radiation of galling insects in apparently harsh environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317803
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  • 9
    Electronic Resource
    Electronic Resource
    Parasitoid pressure and the radiation of a gallforming group (Cecidomyiidae: Asphondylia spp.) on creosote bush (Larrea tridentata) (1989)
    Springer
    Oecologia 79 (1989), S. 293-299 
    Details
    ISSN: 1432-1939
    Keywords: Parasitism ; Gallforming ; Community organization ; Enemy impact hypothesis ; Larrea tridentata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We tested the Enemy Impact Hypothesis, which predicts that communities of one tropic level are organized by the tropic level above. In the case of gallforming insect communities, the hypothesis predicts that gall morphology will diverge, minimizing the number of parasitoids shared among species. We used the monophyletic group of gallforming cecidomyiids (Asphondylia spp.) on creosote bush (Larrea tridentata) to test this hypothesis, predicting that species with thicker gall walls should exclude species of parasitoids with shorter ovipositors and have lower levels of parasitism. Of 17 parasitoid species reared from Asphondylia galls on creosote bush, 9 accounted for over 98% of parasitism. Seven of these 9 species had ovipositors long enough to penetrate 10 of 13 gall morphs measured. There was no significant relationship between gall wall thickness and number of associated parasitoid species (r 2=0.01, P〉0.05, n=13). There was no relationship between gall wall thickness and types of parasitoid species colonizing galls: parasitoids with the shortest ovipositors colonized all types of gall morphs and were dominant members of the parasitoid assemblages in galls with the thickest walls. Ultimately, there were no significant differences in percent parasitism among Asphondylia species, regardless of gall wall thickness. We found no difference in numbers of associated parasitoids or percent parasitism in galls with different textures (e.g. hairy versus smooth), different locations on the plant or different phenologies. Our results suggest that enemy impact has not influenced the diversity of this gall community. Gall wall thickness, phenology, location on the plant and surface structure do not appear to influence the distribution of parasitoid species. Other explanations are offered to account for diversity in gall morphology among these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00384307
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  • 10
    Electronic Resource
    Electronic Resource
    Facultative sex ratio shifts by a herbivorous insect in response to variation in host plant quality (1992)
    Springer
    Oecologia 92 (1992), S. 153-161 
    Details
    ISSN: 1432-1939
    Keywords: Euura lasiolepis ; Sawfly ; Willow ; Sex ratio ; Plant quality hypothesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We tested predictions of sex allocation theory with a series of field experiments on sex allocation in an herbivorous, haplodiploid, sawfly, Euura lasiolepis. Our experiments demonstrated the following points. 1) Adult females allocated progeny sex in response to plant growth. 2) Population sex ratios varied in response to plant quality, being male-biased where plant growth was slow and female-biased where plant growth was rapid. 3) Family sex ratios varied in response to plant quality, being male-biased on slow-growing plants and female-biased on rapidly-growing plants. 4) Female fitness increased more rapidly as the result of developing on more rapidly-growing plants than male mass. We conclude from these results that there are unequal returns on investment in male and female progeny. This results in facultatively biased sawfly sex ratios as an adaptive response to variation in plant quality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317357
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