Abundanz von Getreideaphiden im Winterweizen in Abhängigkeit von Bewirtschaftunggssystemen mit unterschiedlicher Stickstoff-Intensität

The reorganisation from conventional to organic farming practice on a farm located in Northern Germany was accompanied in a long term monitoring to survey the abun-dances of cereal aphids and their natural enemies in winter wheat. The research project focuses on the interactions of host plant and aphids in ecological crop rotation systems differing in their amount of legumes (nitrogen intensive, nitrogen extensive system). Additionally manure treated winter wheat plots established in both ecological crop rota-tion systems were investigated. For comparison the abundance of aphids in conventional farming systems with winter wheat fields nearby were also monitored. The results indi-cate that within the triannual investigation period, aphids significantly varied both in abundance and species composition with regard to the various nitrogen levels. The ear dwelling species Sitobion avenae exhibited the highest damage potential and was sub-stantially less influenced by the extensive conditions of organic farming practice in con-trast to Metopolophium dirhodum and Rhopalosiphum padi sucking on the flag leaves and on lower leaf parts, respectively

Terahertz surface plasmon polariton propagation and focusing on periodically corrugated metal wires

In this letter we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.Comment: accepted at PRL, submitted 29th May 200

Do undersowings in maize influence the development of larvae of the western corn rootworm?

Beeinflussen Untersaaten in Mais die Entwicklung der Larven des Westlichen Maiswurzelbohrers

Dynamic Tuning of Mean Carrier Momentum Relaxation Time in InGaAs InAlAs THz Photoconductive Switches

The carrier transport in InGaAs InAlAs multilayer heterostructures used for the implementation of terahertz (THz) photoconductive antennas is investigated under the injection of a continuous optical wave. By varying the amplitude level of the continuous optical wave in the transmitter or receiver antennas used in a conventional pulsed THz time-domain spectrometer, the amplitude of the detected photocurrent can be controlled without affecting its bandwidth. Unlike increasing the optical power of the pulsed signal, it is shown that raising the continuous optical power results in a reduction of the measured photocurrent. This lowering of the conductivity can be explained by changes in the instantaneous carrier momentum relaxation time in the material rather than variations of the free carrier density level. This behavior affects in systems showing optical continuous-wave components, as, for example, fiber-based THz time-domain spectrometers including optical amplifiers.This work was supported in part by the Spanish Ministry of Economy and Competitiveness through Project TEC2012-35797 and FPU Grant 12/02847.Bockelt, AS.; Vidal Rodriguez, B. (2017). Dynamic Tuning of Mean Carrier Momentum Relaxation Time in InGaAs InAlAs THz Photoconductive Switches. IEEE Transactions on Terahertz Science & Technology. 7(1):107-113. https://doi.org/10.1109/TTHZ.2016.2636742S1071137

Multitrophic interactions among Western Corn Rootworm, Glomus intraradices and microbial communities in the rhizosphere and endorhiza of maize

The complex interactions among the maize pest Western Corn Rootworm (WCR), Glomus intraradices (GI-recently renamed Rhizophagus intraradices) and the microbial communities in both rhizosphere and endorhiza of maize have been investigated in view of new pest control strategies. In a greenhouse experiment, different maize treatments were established: C (control plants), W (plants inoculated with WCR), G (plants inoculated with GI), GW (plants inoculated with GI and WCR). After 20 days of WCR root feeding, larval fitness was measured. Dominant arbuscular mycorrhizal fungi (AMF) in soil and maize endorhiza were analyzed by cloning of 18S rRNA gene fragments of AMF, restriction fragment length polymorphism and sequencing. Bacterial and fungal communities in the rhizosphere and endorhiza were investigated by denaturing gradient gel electrophoresis of 16S rRNA gene and ITS fragments, PCR amplified from total community DNA, respectively. GI reduced significantly WCR larval development and affected the naturally occurring endorhiza AMF and bacteria. WCR root feeding influenced the endorhiza bacteria as well. GI can be used in integrated pest management programs, rendering WCR larvae more susceptible to predation by natural enemies. The mechanisms behind the interaction between GI and WCR remain unknown. However, our data suggested that GI might act indirectly via plant-mediated mechanisms influencing the endorhiza microbial communities