1,710 research outputs found
Egg parasitoid exploitation of plant volatiles induced by single or concurrent attack of a zoophytophagous predator and an invasive phytophagous pest
Zoophytophagous insect predators can induce physiological responses in plants by activating defence signalling pathways, but whether plants can respond to facultative phytophagy by recruiting natural enemies remains to be investigated. In Y-tube olfactometer bioassays, using a system including a Vicia faba plant, the zoophytophagous predator Podisus maculiventris and the egg parasitoid Telenomus podisi, we first demonstrated that T. podisi females are attracted by broad bean plants damaged by feeding activity of P. maculiventris and on which host egg masses had been laid, while they are not attracted by undamaged plants or plants damaged by feeding activity alone. In a second experiment, we evaluated the impact of the invasive phytophagous pest Halyomorpha halys on this plant volatile-mediated tritrophic communication. Results showed that the invasive herbivorous adults do not induce plants to recruit the native egg parasitoid, but they can disrupt the local infochemical network. In fact, T. podisi females are not attracted by volatiles emitted by plants damaged by H. halys feeding alone or combined with oviposition activity, nor are they attracted by plants concurrently infested by P. maculiventris and H. halys, indicating the specificity in the parasitoid response and the ability of the invasive herbivore in interrupting the semiochemical communication between plants and native egg parasitoids. To the best of our knowledge, this is the first study showing that zoophytophagous predator attacks induce indirect plant defences similarly to those defence strategies adopted by plants as a consequence of single or concurrent infestations of herbivorous insects
Suppression of Supercontinuum Generation with Circularly Polarized Light
Controlling a nonlinear process like supercontinuum generation (SG) with the
polarization-state of laser is an important demonstration of laser selectivity.
We show that the threshold for SG and the total amount of supercontinuum
generated depends on incident laser polarization for isotropic samples.
Irrespective of the nature of the samples chosen, SG efficiency decreases as
the incident laser polarization changes from linear to circular and thus,
provides the first experimental demonstration of the suppression of SG with
circularly polarized light. The ratio of the overall SG between the linear and
circular polarization (i.e., measure of suppression) undergoes an intensity
dependent decrease from large initial values to asymptotic limits, irrespective
of samples.Comment: Optics Communications, in pres
Inconsistent genetic structure among members of a multitrophic system: did bruchid parasitoids (Horismenus spp.) escape the effects of bean domestication?
Anthropogenic range expansion and cultural practices have modified the distribution, abundance and genetic diversity of domesticated organisms, thereby altering multitrophic assemblages through space and time. The putative Mesoamerican domestication centre of the common bean, Phaseolus vulgaris L., in Mexico allows investigating the effects of plant domestication on the genetic structure of members of a multitrophic system. The aim of this study was to compare the evolutionary history of Horismenus parasitoids (Hymenoptera: Eulophidae) to those of their bruchid beetle hosts (Coleoptera: Bruchidae) and their domesticated host plant (P. vulgaris), in the context of traditional agriculture in Mexico. We analyzed the population genetic structure of four Horismenus species in Mexico using mitochondrial COI haplotype data. The two most abundant parasitoid species were Horismenus depressus and Horismenus missouriensis. Horismenus missouriensis were infected by Wolbachia endosymbionts and had little to no population differentiation (F ST=0.06). We suspect the mitochondrial history of H. missouriensis to be blurred by Wolbachia, because differentiation among infected vs. non-infected individuals exists (F ST=0.11). Populations of H. depressus were found to be highly differentiated (F ST=0.34), but the genetic structuring could not be explained by tested spatial components. We then compared the genetic structure observed in this parasitoid species to previously published studies on bruchid beetles and their host plants. Despite extensive human-mediated migration and likely population homogenization of its two Acanthoscelides bruchid beetle hosts, H. depressus populations are structured like its host plant, by a recent dispersal from a diverse ancestral gene pool. Distinct evolutionary dynamics may explain inconsistent patterns among trophic levels. Parasitoids likely migrate from wild bean populations and are poorly adapted to bean storage conditions similar to their bruchid beetle hosts. Integrating several trophic levels to the study of evolutionary history has proven to be fruitful in detecting different ecological responses to human-mediated disturbances and host parasite interaction
Light Filaments Without Self Guiding
An examination of the propagation of intense 200 fs pulses in water reveals
light filaments not sustained by the balance between Kerr-induced self-focusing
and plasma-induced defocusing. Their appearance is interpreted as the
consequence of a spontaneous reshaping of the wave packet form a gaussian into
a conical wave, driven by the requirement of maximum localization, minimum
losses and stationarity in the presence of non-linear absorption.Comment: Submitted to Phys. Rev. Lett. on July 7th, 200
Southern Extension to the Breeding Range of the Gyrfalcon, Falco Rusticolus, in Eastern North America
We report the observation of four gyrfalcon (Falco rusticolus) nests and several adults south of the previously recognized southern limit of the species' breeding distribution in eastern North America. Our southernmost observations extends the known breeding range approximately 400 km to the south. The northern forest tundra biome could delineate the southern limit to the breeding range of the gyrfalcon.Nous rapportons la découverte de quatre nids de faucon gerfaut et la mention de quelques adultes au sud de la limite connue de l'aire de reproduction de l'espèce dans l'est de l'Amérique du Nord. Notre observation la plus méridionale étend l'aire de répartition quelques 400 km plus au sud. Les limites sud de la toundra forestière septentrionale pourraient coincider avec celle de l'aire de reproduction du faucon gerfaut.Mots clés: faucon gerfaut, nicheur, répartition, Baie d’Hudson, Québec
First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
The first direct mass-measurement of He has been performed with the
TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the
mass of He was determined with improved precision over our previous
measurement. The obtained masses are (He) = 6.018 885 883(57) u and
(He) = 8.033 934 44(11) u. The He value shows a deviation from
the literature of 4. With these new mass values and the previously
measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and
1.959(16) fm for He and He respectively. We present a detailed
comparison to nuclear theory for He, including new hyperspherical harmonics
results. A correlation plot of the point-proton radius with the two-neutron
separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure
Highly charged ions in Penning traps, a new tool for resolving low lying isomeric states
The use of highly charged ions increases the precision and resolving power,
in particular for short-lived species produced at on-line radio-isotope beam
facilities, achievable with Penning trap mass spectrometers. This increase in
resolving power provides a new and unique access to resolving low-lying
long-lived ( ms) nuclear isomers. Recently, the keV
(determined from -ray spectroscopy) isomeric state in Rb has
been resolved from the ground state, in a charge state of with the TITAN
Penning trap at the TRIUMF-ISAC facility. The excitation energy of the isomer
was measured to be keV above the ground state. The extracted
masses for both the ground and isomeric states, and their difference, agree
with the AME2003 and Nuclear Data Sheet values. This proof of principle
measurement demonstrates the feasibility of using Penning trap mass
spectrometers coupled to charge breeders to study nuclear isomers and opens a
new route for isomer searches.Comment: 8 pages, 6 figure
Physical properties of printed bank notes subjected to crumple testing. Project 3721
"May 20, 1991.""Institute of Paper Science and Technology ... Maclin S. Hall ... Pierre H. Brodeur."Report submitted to Office of Research and Technology Development, Bureau of Engraving and Printing, U.S. Department of the Treasur
- âŠ