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61.
62.
63.
Sequestration of plant compounds by herbivorous insects as a defense against predators is well documented; however, few studies
have examined the effectiveness of sequestration as a defense against parasitoids. One assumption of the “nasty host” hypothesis
is that sequestration of plant defense compounds is deleterious to parasitoid development. We tested this hypothesis with
larvae of the sequestering sphingid Ceratomia catalpae, which is heavily parasitized by the endoparasitoid Cotesia congregata, despite sequestering high concentrations of the iridoid glycoside catalpol from their catalpa host plants. We collected C. catalpae and catalpa leaves from six populations in the Eastern US, and allowed any C. congregata to emerge in the lab. Leaf iridoid glycosides and caterpillar iridoid glycosides were quantified, and we examined associations
between sequestered caterpillar iridoid glycosides and C. congregata performance. Caterpillar iridoid glycosides were not associated with C. congregata field parasitism or number of offspring produced. Although wasp survival was over 90% in all populations, there was a slight
negative relationship between caterpillar iridoid glycosides and wasp survival. Iridoid glycosides were present in caterpillars
at levels that are deterrent to a variety of vertebrate and invertebrate predators. Thus, our results support the alternative
hypothesis that unpalatable, chemically defended hosts are “safe havens” for endoparasitoids. Future trials examining the
importance of catalpol sequestration to potential natural enemies of C. congregata and C. catalpae are necessary to strengthen this conclusion. 相似文献
64.
The effect of diet on sequestration of iridoid glycosides was examined in larvae of three lepidopteran species. Larvae were
reared upon Plantago major, or P. lanceolata, or switched from one to the other in the penultimate instar. Junonia coenia is a specialist on iridoid glycoside-producing plants, whereas the arctiids, Spilosoma congrua and Estigmene acrea, are both polyphagous and eat iridoid-producing plants. All species sequestered iridoids. The specialist J. coenia sequestered from three to seven times the amounts sequestered by the two generalist species. Junonia coenia iridoid glycoside content depended on diet, and they sequestered from 5 to 15% dry weight iridoid glycosides. Estigmene acrea iridoid glycoside sequestration was relatively low, around 2% dry weight and did not vary with diet. Spilosoma congrua sequestration varied with diet and ranged from approximately 3 to 6% dry weight. 相似文献
65.
G. Brill Y. Chen P. M. Amirtharaj W. Sarney D. Chandler-Horowitz N. K. Dhar 《Journal of Electronic Materials》2005,34(5):655-661
We have carried out a detailed study on the growth of Cd-based II–VI compounds on Si substrates using molecular beam epitaxy
(MBE). CdTe, CdSe, CdSeTe, and CdZnSeTe layers were nucleated and grown on Si(211) substrates in order to study a broad range
of semiconductor properties, such as crystal structure, fundamental bandgap, surface morphology, and defect and dislocation
density as a function of the constituent elements. For structural characterization, we used transmission electron microscopy
(TEM) and x-ray diffraction, which indicated that cubic Cd1-xSexTe material had been grown on Si substrates throughout the entire composition range. Likewise, photoreflectance (PR) and photoluminescence
(PL) were used to measure the optical response in the near bandgap (Eg) region. Results indicated nonrandom ordering of CdSeTe/Si material. Studies on quaternary CdZnSeTe material indicated that
Zn and Se concentrations directly impact surface morphology with extremely smooth surfaces obtained as Zn content is decreased. 相似文献
66.
67.
Jason K. Deane Terry R. Rakes Loren Paul Rees 《Information Technology and Management》2009,10(1):55-65
Over the last decade, telecommunications companies have invested nearly 100 billion dollars in the development of an impressive
fiber optic backbone which is capable of transmitting data at incredible speeds. However, much of this backbone remains unused
because of the data capacity bottleneck which exists at the user level. While various technologies have emerged to provide
greater end-point capacity, many of these are of limited availability due to cost or technical considerations. One promising
technology has been high-speed wireless service. Wireless service has the potential to provide widespread coverage, but the
cost of developing the infrastructure such as antenna towers can be formidable. While models have been developed to assist
in the planning for minimum cost tower placement, these models can be quite large and complex to solve. This paper explores
alternate solution methods based on heuristic approaches which may allow for the solution of much larger tower placement problems. 相似文献
68.
W. Cudlip C. Lysons R. Ley G. Deane H. Stroink F. Roli 《Computers, Environment and Urban Systems》1999,23(6):2607
Several business sectors have identified the potential benefits of a landscape/urban assessment based upon the objective appraisal of the interaction of the cultural and natural landscapes. This paper describes a recently approved project (PLAINS) funded by DGXII of the European Union under the Framework IV Environment and Climate Programme. The aim of this project is to identify the benefits of introducing satellite Earth Observation data into the landscape assessment process and to develop a decision support system that will provide for landscape/urban classification tuned to satisfy specific customer requirements. The system will also allow the exploration of impact assessment (‘what if’) scenarios. The project involves three different business sectors who have inherently similar requirements in landscape assessment. The ‘customer’ organisations involved in the project cover the sectors: regional planning authorities, Estate Agents and tourism. In all, there are 13 partners involved in the project from five countries (UK, Denmark, Germany, Italy, Poland). The initial development of the system will use test sites in the counties of Hereford and Worcester in the UK, with subsequent validation being carried out at sites in Italy (Province of Savona), Germany and Poland. 相似文献
69.
Norbert Büchter Ekkehard Ramm Deane Roehl 《International journal for numerical methods in engineering》1994,37(15):2551-2568
Conventional shell formulations, such as 3- or 5-parameter theories or even 6-parameter theories including the thickness change as extra parameter, require a condensation of the constitutive law in order to avoid a significant error due to the assumption of a linear displacement field across the thickness. This means that the normal stress in thickness direction has to either vanish or be constant. In general, these extra constraints cannot be satisfied explicitly or they Sead to elaborate strain expressions. The main objective of the present study is to introduce directly a complete 3-D constitutive law without modification. Therefore, a 7-parameter theory is utilized which includes a linear varying thickness stretch as extra variable allowing also large strain effects. In order to preserve the basic features of a displacement formulation the extra strain term is incorporated via the enhanced assumed strain concept recently proposed by Simo and Rifai to improve the performance of finite elements. Since the extra strain parameter can be eliminated on the element level after discretization, the formulation preserves the formal structure of a 6-parameter shell theory. The resulting hybrid-mixed shell formulation is applied to large deformation problems with hyperelasticity, small and large strain plasticity. 相似文献
70.
Herbivore-induced plant responses can significantly change as a function of plant developmental stage and previous history
of damage. Yet, empirical tests that assess the combined role of multiple damage events and age-dependent constraints on the
ability of plants to induce defenses within and among tissues are scarce. This question is of particular interest for annual
and/or short-lived perennial plant species, whose responses to single or multiple damage events over a growing season are
likely to interact with ontogenetic constraints in affecting a plant’s ability to respond to herbivory. Using Plantago lanceolata and one of its specialist herbivores, Junonia coenia, we examined the effect of plant ontogeny (juvenile vs. mature developmental stages) and history of damage (single and multiple
damage events early and/or late in the season) on plant responses to leaf damage. Plant responses to herbivory were assessed
as induced chemical defenses (iridoid glycosides) and compensatory regrowth, in both above- and below-ground tissues. We found
that constitutive concentration of iridoid glycosides markedly increased as plants matured, but plant ability to induce chemical
defenses was limited to juvenile, but not mature, plant stages. In addition, induced defenses observed 7 d following herbivory
in juvenile plants disappeared 5 wk after the first herbivory event, and mature plants that varied considerably in the frequency
and intensity of damage received over 5 wk, did not differ significantly in their levels of chemical defenses. Also, only
small changes in compensatory regrowth were detected. Finally, we did not observe changes in below-ground tissues’ defenses
or biomass a week following 50% removal of leaf tissues at either age class or history of damage. Together, these results
suggest that in P. lanceolata and perhaps other systems, ontogenetic trajectories in plant growth and defenses leading to strong age-dependent induced
responses may prevail over herbivore-induced indirect interactions. 相似文献