Effects of four nematode species on fitness costs of pink bollworm resistance to Bacillus thuringiensis toxin Cry1Ac

Evolution of resistance by pests can reduce the efficacy of transgenic crops that produce insecticidal toxins from the bacterium Bacillus thuringiensis Berliner (Bt). In conjunction with refuges of non-Bt host plants, fitness costs can delay the evolution of resistance. Furthermore, fitness costs often vary with ecological conditions, suggesting that agricultural landscapes can be manipulated to magnify fitness costs and thereby prolong the efficacy of Bt crops. In the current study, we tested the effects of four species of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) on the magnitude and dominance of fitness costs of resistance to Bt toxin CrylAc in pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae). For more than a decade, field populations of pink bollworm in the United States have remained susceptible to Bt cotton Gossypium hirsutum L. producing CrylAc; however, we used laboratory strains that had a mixture of susceptible and resistant individuals. In laboratory experiments, dominant fitness costs were imposed by the nematodeSteinernema riobrave Cabanillas, Poinar, and Raulston but no fitness costs were imposed bySteinernema carpocapsae Weiser, Steinernema sp. (ML18 strain), or Heterorhabditis sonorensis Stock, Rivera-Orduño, and Flores-Lara. In computer simulations, evolution of resistance to CrylAc by pink bollworm was substantially delayed by treating some non-Bt cotton refuge fields with nematodes that imposed a dominant fitness cost, similar to the cost observed in laboratory experiments with S. riobrave. Based on the results here and in related studies, we conclude that entomopathogenic nematodes could bolster insect resistance management, but the success of this approach will depend on selecting the appropriate species of nematode and environment, as fitness costs were magnified by only two of five species evaluated and also depended on environmental factors

Effects of Pink Bollworm Resistance to Bacillus thuringiensis on Phenoloxidase Activity and Susceptibility to Entomopathogenic Nematodes

Widespread planting of crops genetically engineered to produce insecticidal toxins from the bacterium Bacillus thuringiensis (Bt) imposes selection on many key agricultural pests to evolve resistance to Bt. Fitness costs can slow the evolution of Bt resistance. We examined effects of entomopathogenic nematodes on fitness costs of Bt resistance in the pink bollworm,Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), a major pest of cotton,Gossypium hirsutum L., in the southwestern United States that is currently controlled by transgenic cotton that produces Bt toxin Cry1Ac. We tested whether the entomopathogenic nematodes Steinernema riobrave Cabanillas, Poinar, and Raulston (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae) affected fitness costs of resistance to Cry1Ac in two laboratory-selected hybrid strains of pink bollworm reared on non-Bt cotton bolls. The nematode S. riobrave imposed a recessive fitness cost for one strain, and H. bacteriophora imposed a fitness cost affecting heterozygous resistant individuals for the other strain. Activity of phenoloxidase, an important component of insects\u27 immune response, did not differ between Bt-resistant and Bt-susceptible families. This suggests phenoloxidase does not affect susceptibility to entomopathogenic nematodes in Bt-resistant pink bollworm. Additionally, phenoloxidase activity does not contribute to Bt resistance, as has been found in some species. We conclude that other mechanisms cause higher nematode-imposed mortality for pink bollworm with Bt resistance genes. Incorporation of nematode-imposed fitness costs into a spatially explicit simulation model suggests that entomopathogenic nematodes in non-Bt refuges could delay resistance by pink bollworm to Bt cotton

Effects of entomopathogenic nematodes on evolution of pink bollworm resistance to Bacillus thuringiensis toxin Cry1Ac

The evolution of resistance by pests can reduce the efficacy of transgenic crops that produce insecticidal toxins from Bacillus thuringiensis (Bt). However, fitness costs may act to delay pest resistance to Bt toxins. Meta-analysis of results from four previous studies revealed that the entomopathogenic nematode Steinernema riobrave (Rhabditida: Steinernematidae) imposed a 20% fitness cost for larvae of pink bollworm, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), that were homozygous for resistance to Bt toxin Cry1Ac, but no significant fitness cost was detected for heterozygotes. We conducted greenhouse and laboratory selection experiments to determine whether S. riobrave would delay the evolution of pink bollworm resistance to Cry1Ac. We mimicked the high dose/refuge scenario in the greenhouse with Bt cotton (Gossypium hirsutum L.) plants and refuges of non-Bt cotton plants, and in the laboratory with diet containing Cry1Ac and refuges of untreated diet. In both experiments, half of the replicates were exposed to S. riobrave and half were not. In the greenhouse, S. riobrave did not delay resistance. In the laboratory, S. riobrave delayed resistance after two generations but not after four generations. Simulation modeling showed that an initial resistance allele frequency \u3e0.015 and population bottlenecks can diminish or eliminate the resistance-delaying effects of fitness costs. We hypothesize that these factors may have reduced the resistance-delaying effects of S. riobrave in the selection experiments. The experimental and modeling results suggest that entomopathogenic nematodes could slow the evolution of pest resistance to Bt crops, but only under some conditions

Gamma ray production in inelastic scattering of neutrons produced by cosmic muons in 56^{56}Fe

We report on the study of the intensities of several gamma lines emitted after the inelastic scattering of neutrons in $^{56}$Fe. Neutrons were produced by cosmic muons passing the 20t massive iron cube placed at the Earth's surface and used as a passive shield for the HPGe detector. Relative intensities of detected gamma lines are compared with the results collected in the same iron shield by the use of $^{252}$Cf neutrons. Assessment against the published data from neutron scattering experiments at energies up to 14 MeV is also provided

Negative hyperon and multiple strange particle production in K̄p interactions at 6 GEV/C

Imperial Users onl

Towards 3D printed multifunctional immobilization for proton therapy: initial materials characterization

Purpose: 3D printing technology is investigated for the purpose of patient immobilization during proton therapy. It potentially enables a merge of patient immobilization, bolus range shifting, and other functions into one single patient-speci c structure. In this rst step, a set of 3D printed materials is characterized in detail, in terms of structural and radiological properties, elemental composition, directional dependence, and structural changes induced by radiation damage. These data will serve as inputs for the design of 3D printed immobilization structure prototypes. Methods: Using four di erent 3D printing techniques, in total eight materials were subjected to testing. Samples with a nominal dimension of 20×20×80 mm3 were 3D printed. The geometrical printing accuracy of each test sample was measured with a dial gage. To assess the mechanical response of the samples, standardized compression tests were performed to determine the Young’s modulus. To investigate the e ect of radiation on the mechanical response, the mechanical tests were performed both prior and after the administration of clinically relevant dose levels (70 Gy), multiplied with a safety factor of 1.4. Dual energy computed tomography (DECT) methods were used to calculate the relative electron density to water ρe, the e ective atomic number Ze , and the proton stopping power ratio (SPR) to water SPR. In order to validate the DECT based calculation of radiological properties, beam measurements were performed on the 3D printed samples as well. Photon irradiations were performed to measure the photon linear attenuation coe cients, while proton irradiations were performed to measure the proton range shift of the samples. The direc- tional dependence of these properties was investigated by performing the irradiations for di erent orientations of the samples. Results: The printed test objects showed reduced geometric printing accuracy for 2 materials (deviation > 0.25 mm). Compression tests yielded Young’s moduli ranging from 0.6 to 2940 MPa. No deterioration in the mechanical response was observed after exposure of the samples to 100 Gy in a therapeutic MV photon beam. The DECT-based characterization yielded Ze ranging from 5.91 to 10.43. The SPR and ρe both ranged from 0.6 to 1.22. The measured photon attenuation coe cients at clinical energies scaled linearly with ρe. Good agreement was seen between the DECT estimated SPR and the measured range shift, except for the higher Ze . As opposed to the photon attenuation, the proton range shifting appeared to be printing orientation dependent for certain materials. Conclusions: In this study, the rst step toward 3D printed, multifunctional immobilization was performed, by going through a candidate clinical work ow for the rst time: from the material printing to DECT characterization with a veri cation through beam measurements. Besides a proof of concept for beam modi cation, the mechanical response of printed materials was also investigated to assess their capabilities for positioning functionality. For the studied set of printing techniques and materials, a wide variety of mechanical and radiological properties can be selected from for the intended purpose. Moreover the elaborated hybrid DECT methods aid in performing in-house quality assurance of 3D printed components, as these methods enable the estimation of the radiological properties relevant for use in radiation therapy

Detailed analysis of the cell-inactivation mechanism by accelerated protons and light ions

Published survival data for V79 cells irradiated by monoenergetic protons, helium-3, carbon, and oxygen ions and for CHO cells irradiated by carbon ions have been analyzed using the probabilistic two-stage model of cell inactivation. Three different classes of DNA damages formed by traversing particles have been distinguished, namely severe single-track damages which might lead to cell inactivation directly, less severe damages where cell inactivation is caused by their combinations, and damages of negligible severity that can be repaired easily. Probabilities of single ions to form these damages have been assessed in dependence on their linear energy transfer (LET) values. Damage induction probabilities increase with atomic number and LET. While combined damages play crucial role at lower LET values, single-track damages dominate in high-LET regions. The yields of single-track lethal damages for protons have been compared with the Monte Carlo estimates of complex DNA lesions, indicating that lethal events correlate well with complex DNA double-strand breaks. The decrease in the single-track damage probability for protons of LET above approx. 30 keV/$\mu$m, suggested by limited experimental evidence, is discussed, together with the consequent differences in the mechanisms of biological effects between protons and heavier ions. Applications of the results in hadrontherapy treatment planning are outlined.Comment: submitted to Physics in Medicine and Biolog

Atmospheric Radiation Measurement Program Climate Research Facility Operations Quarterly Report January 1–March 31, 2011

Individual raw datastreams from instrumentation at the Atmospheric Radiation Measurement (ARM) Climate Research Facility fixed and mobile sites are collected and sent to the Data Management Facility (DMF) at Pacific Northwest National Laboratory (PNNL) for processing in near real-time. Raw and processed data are then sent approximately daily to the ARM Data Archive, where they are made available to users. For each instrument, we calculate the ratio of the actual number of processed data records received daily at the Data Archive to the expected number of data records. The results are tabulated by (1) individual datastream, site, and month for the current year and (2) site and fiscal year (FY) dating back to 1998

ARM Facilities Newsletter

This newsletter contains two articles. The first is about problems at the 60-ft. instrument tower at Okmulgee State Park. Wasps have taken up residency at the tower which has hampered maintenance work there. The second article describes the cloud layer experiment at the Oklahoma site

Atmospheric Radiation Measurement Program Climate Research Facility Operations Quarterly Report April 1 – June 30, 2006

Description. Individual raw data streams from instrumentation at the Atmospheric Radiation Measurement (ARM) Program Climate Research Facility (ACRF) fixed and mobile sites are collected and sent to the Data Management Facility (DMF) at Pacific Northwest National Laboratory (PNNL) for processing in near real time. Raw and processed data are then sent daily to the ACRF Archive, where they are made available to users. For each instrument, we calculate the ratio of the actual number of data records received daily at the Archive to the expected number of data records. The results are tabulated by (1) individual data stream, site, and month for the current year; and (2) site and fiscal year dating back to 1998