1,431 research outputs found
Biological control of Otiorhynchus sulcatus by insect parasitic nematodes, Heterorhabditis spp., at low temperatures : a systems analytical approach
No full textThe black vine weevil, Otiorhynchus sulcatus, is an important pest in ornamentals and nursery stock in The Netherlands. The larvae, which feed on the root system of the plant, can be controlled by insect parasitic nematodes, Heterorhabditis. However, the presently available isolates of the nematode are ineffective at temperatures below 12-13°C, causing problems in black vine weevil control in open cultures. In this study, options to improve control by Heterorhabditis are explored, using a systems analytical approach. First, the nematode behavioural processes involved in host finding and control were studied and characterized. These processes are nematode movement, immobilization and remobilization near the soil surface, accumulation near an attractive insect (arrestment), penetration and aggregation of nematodes among insect hosts. The influence of temperature (9 and 20°C) and host species ( O . sulcatus or the more attractive and susceptible Galleria mellonella) on nematode behaviour was assessed to determine the contribution of these factors to control success. Knowledge of behavioural processes was integrated into a systems simulation model that relates the control success to the underlying behavioural processes. The model simulates movement of nematodes in space and time from the moment of application on a sand column until penetration into a host. The model for O . sulcatus at 9°C was most sensitive to changes in the parameters characterizing aggregation and arrestment. Parameters characterizing penetration, the proportion infectious nematodes and the relative penetration rate, had a moderate effect on model outcome. Options for improvement were evaluated by relating the sensitivity of the model to genetic and phenotypic variation found in the nematodes. The amount of variation was assessed by comparing behavioural traits between and within Heterorhabditis isolates. Aggregation and arrestment are host related and there is little variation in Heterorhabditis for these traits. There is phenotypic variation in the proportion infectious nematodes. The most promising option to enhance control of O . sulcatus by Heterorhabditis at low temperatures is, therefore, to improve production and storage conditions to increase and stabilize the proportion infectious nematodes
Spatial and temporal patterns of carabid activity-density in cereals do not explain levels of predation on weed seeds
No full textSeed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris>P. annua>S. media>L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a fiel
Direct numerical simulation of turbulent Couette-Poiseuille flow with zero skin friction
No full textThe near-wall scaling of mean velocity U(y) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to √yw in the region just above the wall at which the mean shear dU/dy = 0
Scaling and intermittency in ocean turbulence: analysis of coastal water optical properties and sea surface temperature (SST)
No full textWe consider here some scaling and intermittency properties of oceanic turbulence, with a general aim of considering the impact of turbulence on the bio-optical dynamics. For that purpose, we tried two different approaches, using in situ and satellite data. For the in situ study we adopted one dimensional and for the satellite two dimensional approaches. Different techniques such as Fourier power spectrum, Empirical mode of decomposition (EMD), Hilbert spectral analysis (HSA) have been used for analyzing the intermittency characteristics of the in situ data. For analyzing the multi-scale properties of the satellite images, we have considered Structure functions (SF) and Fourier power spectrum (1D and 2D). The general objective is to understand the multi-scale oceanic variability using scaling tools developed in the field of intermittent turbulence studies
The organization of industry in the P.R. China: A new start or resort to old concepts?
No full textThe Chinese have let it be known since the death of Mao Zedong and the purge of the “Gang of Four” that they would in future draw on credits from foreign governments as well as other sources to finance imports of technology. According to western conjectures China’s capital requirements may be between US $ 25 and 50 bn or even a good deal higher. Many observers have taken the view that the Chinese have thereby put all their former development principles behind them. The author of the following article was in the P.R. China about the middle of this year at the invitation of the National Planning Commission. His assessment is that the P.R. China is far from embarking on an entirely new course in its development policy
Comparative vertical migration of insect parasitic nematodes Heterorhabditis spp. and Steinernema spp. in sand at 9°C
No full textThe influence of time of storage on performance of the insect parasitic nematode, Heterorhabditis sp.
No full textThe influence of time of storage on performance of the insect parasitic nematode, Heterorhabditis sp.
No full textConstant approximation for virtual backbone construction with guaranteed routing cost in wireless sensor networks
No full textLinear regression models describing the performance of the insect parasitic nematode, Heterorhabditis sp., during storage
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