Search Results (6)

Traditionally, harmonic RADAR has tracked insects using a non-linear diode tag, illuminated by an extremely high-power (up to 20 kW) radio signal. This work introduces a battery-less, semiconductor-free passively modulating tag that operates with low incident power and stands out against clutter. This metamaterial-inspired tag is unique, using an animal’s movement to vary its resonant frequency and modulating the backscattered signal for enhanced detection. This means that the tag does not require its own power source, while still allowing inference about the subject’s behaviour. It consists of two coupled elements; the resonant scattering frequency is defined by the angle between them. This tag can be manufactured easily since it consists solely of two substrates and copper tracks. At a 0° angle, the tag is modelled and measured with an RCS of −31 dBsm at 3.6 GHz (50 dB greater than a bee), and its frequency tunes from 3.75 to 3.95 GHz over the angle variation. Full article

Silicon (Si) accumulation is a widespread anti-herbivore defence in grasses, yet little is known about how insects counteract silicification, including via compensatory feeding, or whether Si-mediated changes in plant stoichiometry also influence herbivore performance. We examined how Si supplementation alters foliar Si, carbon (C), nitrogen (N), and phosphorus (P) in two grasses with contrasting accumulation strategies, Brachypodium distachyon (high accumulator) and Lolium arundinaceum (moderate accumulator), and the consequences for growth and feeding by Helicoverpa armigera. Plants were grown hydroponically with or without Si, and herbivore relative growth rate (RGR), relative consumption (RC), and Efficiency of Conversion of Ingested food (ECI) were measured. Si supplementation had stronger effects on herbivore performance in B. distachyon compared with L. arundinaceum. RGR declined by 126% on B. distachyon compared with 40% on L. arundinaceum. Herbivores increased RC on Si-supplemented L. arundinaceum, with RC positively correlated with foliar Si concentrations, but no compensatory feeding occurred on B. distachyon. N and P concentrations were positively correlated with RGR in L. arundinaceum and ECI in B. distachyon. In conclusion, the degree of Si accumulation in grasses influences both plant stoichiometry and has contrasting impacts on herbivore feeding strategies. Full article

Entomological radar is a specially designed instrument that can measure the behavioral and biological characteristics of high-altitude migrating insects. Its application is of great significance for the monitoring, early warning, and control of agricultural pests. As an important component of the local migratory biomass, insects fly in the air during the day and night. The fully polarimetric entomological radar was carefully designed with all-day, all-weather, and multi-function measurement capabilities. The fully polarimetric entomological radar measures the mass of a single insect based on the radar cross-sectional (RCS) measurement and then calculates the biomass of migrating insects. Therefore, the measurement accuracy of the insect RCS is the key indicator affecting the accuracy of migratory biomass statistics. Due to the radar’s lack of in-beam angle measurement ability, the insect RCS is usually measured based on the assumption that the insect is on the beam center. Therefore, the measured RCS will be smaller than true value if the insect deviates from the beam center due to the gain curve of the antenna. This leads to measurement errors in regard to the insect mass and migratory biomass. In order to solve this problem, a biomass estimation method, reported in this paper, was designed under the assumption of a uniform distribution of migrating insects in the radar monitoring airspace. This method can estimate the individual RCS expectation of migrating insects through a statistical method without measuring the position of the insects in the beam and then obtain the migratory biomass. The effectiveness of the model and algorithm is verified by simulations and entomological radar field measurements. Full article

Measuring migration flux with entomological radar is of great importance to assess the biomass of migratory insects and study the influence of insects on the ecosystem. However, the migration flux is measured with a large quantity of errors for the entomological radar without the ability of in-beam angle measurement, because the insect RCS is measured with the assumption that the insect flies over the beam center. When the insect does not pass through the beam center, the measured RCS is less than the true value. To improve the estimation accuracy of migration flux, a new estimation method of migration flux based on statistical hypothesis is proposed for radars working in the fixed-beam vertical-looking mode. This method avoids the RCS measurement error caused by the offset of the insect trajectory to the radar beam center by assuming that the insect flight trajectory is evenly distributed in the beam and calculating the average value of flux. This method is extended to be used in fixed-beam arbitrary pointing mode and a new proposed scanning mode. The effectiveness of the proposed method is verified by simulations and migration insect data measured by a radar. Full article

The root-feeding scarab insect Costelytra giveni causes severe damage to pasture ecosystems in New Zealand. Loline alkaloids produced by some Epichloë endophytes deter this insect. In two experiments, tall fescue infected with E. coenophiala, strain AR584, and endophyte-free (Nil) controls were subjected to pulse drought stress (DS) or well-watered conditions (WW). The second experiment also included meadow fescue infected with E. uncinata. After 4–6 weeks exposure to the different conditions, roots were excised and fed to C. giveni larvae for 7 days. Relative root consumption (RC), frass production, and relative weight change (RWC) of larvae were measured and the loline content of roots determined. RC and frass output were higher for larvae feeding on Nil DS tall fescue than WW and reduced by AR584. RWC was also greater on DS than on WW Nil plants but reduced by endophyte only in DS plants. RC, frass output, and RWC of larvae were reduced by endophyte in DS and WW meadow fescue, but the effect was greater for WW plants. Loline alkaloid concentration in roots was significantly higher in DS than WW tall fescue in Experiment I but higher in WW than DS meadow fescue in Experiment II. These experiments have demonstrated that moisture status interacts with endophyte to differentially affect root herbivory in tall fescue and meadow fescue. Full article

Migratory insect identification has been concerning entomology and pest managers for a long time. Their nocturnal behavior, as well as very small radar cross-section (RCS), makes individual detection challenging for any radar network. Typical entomological radars work at the X-band (9.4 GHz) with a vertical pencil beam. The measured RCS can be used to estimate insect mass and wingbeat frequency, and then migratory insects can be categorized into broad taxon classes using the estimated parameters. However, current entomological radars cannot achieve species identification with any higher precision or confidence. The limited frequency range of current insect radars have precluded the acquisition of more information useful for the identification of individual insects. In this paper, we report an improved measurement method of insect mass and body length using a radar with many more measurement frequencies than current entomological radars. The insect mass and body length can be extracted from the multi-frequency RCSs with uncertainties of 16.31% and 10.74%, respectively. The estimation of the thorax width and aspect ratio can also be achieved with uncertainties of 13.37% and 7.99%, respectively. Furthermore, by analyzing the statistical data of 5532 insects representing 23 species in East China, we found that the correct identification probabilities exceed 0.5 for all of the 23 species and are higher than 0.8 for 15 of the 23 species under the achievable measurement precision of the proposed technique. These findings provide promising improvements of individual parameter measurement for entomological radars and imply a possibility of species identification with higher precision. Full article