Matching commercial thrips predating phytoseids with the highly diversified climatic conditions of different strawberry production systems

Flower inhabiting thrips (Order: Thysanoptera) are a major threat to fruit quality in strawberry production around the world. As chemical control is often inefficient, alternative control measures are of broad and current interest. Their fast reproduction makes predatory mites highly suitable for thrips control in a crop with a relatively short cropping season like strawberry. However, climatic conditions of strawberry production can differ strongly depending on the production system (glasshouse, plastic tunnel, open field, etc.) and the time span of cultivation (depending mostly on planting date and the type of cultivar: summer-or everbearing). As predatory mites typically display a temperature-dependent life history and the current commercially available thrips predating phytoseids vary in geographic origin, one can assume that under certain climatic conditions some species will be more applicable than others. The goal of this study is to determine which species are suitable for which climatic conditions. Therefore all (Belgian) production systems and time spans are categorized into three climate types, simulated in the laboratory. The population build-up of seven predatory mite species (A. degenerans, A. montdorensis, A. andersoni, A. limonicus, A. swirskii, N. cucumeris and E. gallicus) were assessed for each of these climatic conditions. Under the coldest condition (A), the in West-Europe indigenous E. gallicus was the only species with a significant population build up. When moderate conditions (B) were simulated E. gallicus, N. cucumeris and A. limonicus were most successful. The warmest regime (C) was most adequate for E. gallicus and A. swirskii

Prevalence of Toxoplasma gondii in Belgian wildlife

De Craeye, S., Speybroeck, N., Baert, K., Ajzenberg, D., Dardé, M.L., Collinet, F., Tavernier, P., Van Gucht, S., Dorny, P., Dierick, K

Prevalence of Toxoplasma gondii infection in Myocastor coypus in a protected Italian wetland

<p>Abstract</p> <p>Background</p> <p><it>Toxoplasma gondii </it>is the causative agent for a major zoonosis with cosmopolitan distribution. Water has been implicated in outbreaks of toxoplasmosis in recent years. Coypus (<it>Myocastor coypus</it>), commonly nutria, are large semi-aquatic invasive rodents, naturalized throughout European countries, including most wetlands of Central Italy. The habitat of these animals is both terrestrial and aquatic, making them a species highly exposed to the parasite.</p> <p>Findings</p> <p>The occurrence of the infection was evaluated using a modified agglutination test (MAT) in 74 adult coypus from a naturalized population living in a wetland of Central Italy. Nested PCR (n-PCR) assay was carried out on some of them. Positive <it>T. gondii </it>MAT results were found in 44 animals (59·4%), 30 males (68·2%) and 14 females (31·8%). Antibody titers were ranging from 20 to 40960, while 12 out of 23 (52·2%), examined animals, 8 males (66·7%) and 4 females (33·3%), resulted positive to n-PCR. All n-PCR positive animals were seropositive, showing antibody titers ranging from 640 to 40960.</p> <p>Conclusions</p> <p>Our results indicate that examined animals are heavily parasitized with <it>Toxoplasma</it>. This suggests that coypus could be a reservoir of this parasite, because they can be eaten both by scavenger animals and by humans, and that these animals would play a role in maintaining the cycle of <it>T. gondii</it>.</p

Drop size effects on rain-generated ring-waves with a view to remote sensing applications

This paper presents an analysis of drop size effects on ring-wave spectra and radar scatterometer returns from a water surface agitated by artificial rain. For this purpose, monodisperse and polydisperse rain events were generated in the laboratory for a wide range of rain rates and various drop sizes. The water droplets reached the surface at terminal velocity. In all cases, the radar average power is well modelled by a linear function of the power spectral density at the Bragg resonant wavelength. The drop size is found to have a strong impact on the spectral shape of the ring-waves and on their total energy. A log-Gaussian model characterizes well the ring-wave spectra and empirical expressions of the spectrum parameters are given. Ring-wave energy increases with rain rate and drop size. and is found to be proportional to the kinetic energy of a single drop, indicating that one may use a model in which all drops contribute to the ring-wave energy in proportion to their squared momentum. The results from the monodisperse rain experiments are used to construct a model for natural rain. Data from the polydisperse rain experiments show that a nonlinear model which relates dissipation to the total rainfall rate provides excellent agreement with the measurements. This analysis also shows the important impact of a few large drops on the ring-wave spectrum. The model proposed can be extended to natural rains either by using measurements of the drop size distribution or by assuming a drop size distribution model that is appropriate to the study region. It is concluded that it is important to characterize ring-wave spectra as a function of rain rate and drop size distribution to develop robust radar scattering models for rain-roughened seas

Numerical analysis of modulated metasurface antennas using Fourier-Bessel basis functions

International audienceMetasurfaces are thin (2D) metamaterials designed for manipulating the dispersion properties of surface-waves (SWs) or the reflection properties of incident plane-waves. Thanks to the sub-wavelength sizes of the patches used in the implementation step, these surfaces can be described by a surface impedance boundary condition (IBC). In this paper, we investigate a 'Method of Moments' (MoM) based analysis of such surface with a family of entire-domain basis functions named 'Fourier-Bessel' functions. The orthogonality property of these functions on a disk allows us to represent any smooth current distribution in an effective manner and thereby to drastically reduce the size of the MoM matrix. © 2017 IEEE

Three-Dimensional Reconstruction of the Oscillatory Free-Surfaces of a Flow over Antidunes: Stereoscopic and Velocimetric Techniques

We present imaging methods developed to characterize the oscillatory free-surface of rapid flows and apply them to torrential currents propagating over sediment antidunes. The aim is to obtain high-resolution relief maps of the free-surface topography, in order to highlight the regular spatial patterns associated with the bedforms. Two measurement principles are outlined and tested, both based on the imaging of floating tracers dispersed on the rapidly flowing surface. The first relies on direct stereoscopic measurements obtained using two cameras, while the second exploits an original velocimetric principle allowing to derive elevation from the velocity field acquired using a single camera. The measurement procedures and image analysis algorithms are introduced for the two methods, along with the physical assumptions underlying the velocimetric principle. The results of the two techniques are compared for different free-surface patterns and good correspondence is obtained. The obtained relief maps vividly depict the variety of motifs that can evolve as a result of interaction between shallow flows and loose sediment beds