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Selected AbstractsExamining the single and interactive effects of three insecticides on amphibian metamorphosis,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2008Michelle D. Boone Abstract Although aquatic communities frequently are exposed to a number of pesticides, the effects of chemical mixtures are not well understood. In two separate studies, I examined how insecticide mixtures influenced the likelihood of unpredictable, nonadditive effects on American toad (Bufo americanus) and green frog (Rana clamitans) tadpoles reared in outdoor aquatic communities. I exposed tadpoles to single or multiple insecticides at approximately half the reported median lethal concentrations using insecticides that were either acetylcholinesterase inhibitors (carbaryl or malathion) or a sodium-channel disruptor (permethrin). I found that combinations of insecticides with the same mode of action were more likely to have nonadditive effects on amphibian metamorphosis compared with those having different modes of action. Additionally, in one study, a commercial formulation of permethrin led to near-complete elimination of American toads, suggesting that this formulation could have adverse effects on aquatic communities. Many community studies exploring the ecological effects of expected environmental concentrations of pesticides have suggested that indirect effects in the food web, rather than direct effects on individual physiology, have the largest effect on amphibians. The present study indicates that direct effects of pesticides may become particularly important when insecticides with the same mode of action are present in the environment. [source] Algal toxicity of nitrobenzenes: Combined effect analysis as a pharmacological probe for similar modes of interactionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2005Rolf Altenburger Abstract An analysis regarding the effects of the mixture toxicity of different nitrobenzenes on the reproduction of the green alga Scenedesmus vacuolatus was undertaken using the concepts of concentration addition and response addition. Using lipophilicity-based quantitative structure-activity relationship (QSAR) modeling for nitrobenzenes, the assumption is held that mononitrobenzenes may exert narcotic effects as a common type of action, whereas dinitrobenzenes show a somewhat greater toxicity. From the literature, QSARs based on quantum chemical parameters suggest that some mononitrobenzenes may be effective through additional other modes of action. The toxicity of a mixture of 14 nitrobenzenes clearly exceeds the predicted combined effects, as expected for the sum of toxic units from a uniform narcotic mode of action. Moreover, the observed combined effect is smaller than that predicted from similarly acting compounds calculated on the basis of the parameterized dose-response functions using concentration addition. Further modeling of the combined effect, joining the models of concentration addition for components with anticipated similar modes of action and of response addition for those with independent action, led us to propose that not all nitrobenzenes follow the same mode of action. This idea is in line with the hypothesis derived from quantum chemical QSAR considerations. Most interestingly, the methodology introduced here uses combined effect analysis as a pharmacological probe to test for similarity in the mode of action of mixture components. [source] Trend and variability of China precipitation in spring and summer: linkage to sea-surface temperaturesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2004Fanglin Yang Abstract Observational records in the past 50 years show an upward trend of boreal-summer precipitation over central eastern China and a downward trend over northern China. During boreal spring, the trend is upward over southeastern China and downward over central eastern China. This study explores the forcing mechanism of these trends in association with the global sea-surface temperature (SST) variations on the interannual and interdecadal time scales. Results based on singular value decomposition (SVD) analyses show that the interannual variability of China precipitation in boreal spring and summer can be well defined by two centres of action for each season, which are covarying with two interannual modes of SSTs. The first SVD modes of precipitation in spring and summer, which are centred in southeastern China and northern China respectively, are linked to an El Niño,southern oscillation (ENSO)-like mode of SSTs. The second SVD modes of precipitation in both seasons are confined to central eastern China, and are primarily linked to SST variations over the warm pool and the Indian Ocean. Features of the anomalous 850 hPa winds and 700 hPa geopotential height corresponding to these modes support a physical mechanism that explains the causal links between the modal variations of precipitation and SSTs. On the decadal and longer time scale, similar causal links are found between the same modes of precipitation and SSTs, except for the case of springtime precipitation over central eastern China. For this case, while the interannual mode of precipitation is positively correlated with the interannual variations of SSTs over the warm pool and Indian Ocean, the interdecadal mode is negatively correlated with a different SST mode, i.e. the North Pacific mode. The latter is responsible for the observed downward trend of springtime precipitation over central eastern China. For all other cases, both the interannual and interdecadal variations of precipitation can be explained by the same mode of SSTs. The upward trend of springtime precipitation over southeastern China and downward trend of summertime precipitation over northern China are attributable to the warming trend of the ENSO-like mode. The recent frequent summertime floods over central eastern China are linked to the warming trend of SSTs over the warm pool and Indian Ocean. Copyright © 2004 Royal Meteorological Society [source] Differential mechanisms for the inhibition of human cytochrome P450 1A2 by apigenin and genisteinJOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2010Hideaki Shimada Abstract The inhibitory effects of flavonoids on the human cytochrome P450 1A2 (CYP1A2) were examined. Among flavonoids tested, galangin, kaempferol, chrysin, and apigenin were potent inhibitors. Although apigenin belonging to flavones and genistein belonging to isoflavones are similar in the chemical structures, the inhibitory potencies for CYP1A2 were distinguished markedly between these two flavonoids. In computer-docking simulation, apigenin interacted with the same mode of cocrystallized ,-naphthoflavone in the active site of CYP1A2, and then the B ring of apigenin was placed close to the heme iron of the enzyme with a single orientation. In contrast, the docked genistein conformation showed two different binding modes, and the A ring of genistein was oriented to the heme iron of CYP1A2. Furthermore, the binding free energy of apigenin was lower than that of genistein. These results demonstrate a possible mechanism that causes the differential inhibitory potencies of apigenin and genistein for CYP1A2. © 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 24:230,234, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/jbt.20328 [source] Interspecific variation in primary seed dispersal in a tropical forestJOURNAL OF ECOLOGY, Issue 4 2008Helene C. Muller-Landau Summary 1We investigated the relationships of seed size, dispersal mode and other species characteristics to interspecific variation in mean primary seed dispersal distances, mean annual seed production per unit basal area, and clumping of seed deposition among 41 tropical tree species on Barro Colorado Island, Panama. 2A hierarchical Bayesian model incorporating interannual variation in seed production was used to estimate seed dispersal, seed production, and clumping of seed rain for each species from 19 years of data for 188 seed traps on a 50-ha plot in which all adult trees were censused every 5 years. 3Seed dispersal was modelled as a two-dimensional Student's T distribution with the degrees of freedom parameter fixed at 3, interannual variation in seed production per basal area was modelled as a lognormal, and the clumping of seed rain around its expected value was modelled as a negative binomial distribution. 4There was wide variation in seed dispersal distances among species sharing the same mode of seed dispersal. Seed dispersal mode did not explain significant variation in seed dispersal distances, but did explain significant variation in clumping: animal-dispersed species showed higher clumping of seed deposition. 5Among nine wind-dispersed species, the combination of diaspore terminal velocity, tree height and wind speed in the season of peak dispersal explained 40% of variation in dispersal distances. Among 31 animal-dispersed species, 20% of interspecific variation in dispersal distances was explained by seed mass (a negative effect) and tree height (a positive effect). 6Among all species, seed mass, tree height and dispersal syndrome explained 28% of the variation in mean dispersal distance and seed mass alone explained 45% of the variation in estimated seed production per basal area. 7Synthesis. There is wide variation in patterns of primary seed rain among tropical tree species. Substantial proportions of interspecific variation in seed production, seed dispersal distances, and clumping of seed deposition are explained by relatively easily measured plant traits, especially dispersal mode, seed mass, and tree height. This provides hope for trait-based generalization and modelling of seed dispersal in tropical forests. [source] Comparative analysis of neonicotinoid binding to insect membranes: I. A structure,activity study of the mode of [3H]imidacloprid displacement in Myzus persicae and Aphis craccivoraPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 10 2004Dr Hartmut Kayser Abstract Neonicotinoids bind selectively to insect nicotinic acetylcholine receptors with nanomolar affinity to act as potent insecticides. While the members of the neonicotinoid class have many structural features in common, it is not known whether they also share the same mode of binding to the target receptor. Previous competition studies with [3H]imidacloprid, the first commercialised neonicotinoid, indicated that thiamethoxam, representing a novel structural sub-class, may bind in a different way from that of other neonicotinoids. In the present work we analysed the mode of [3H]imidacloprid displacement by established neonicotinoids and newly synthesized analogues in the aphids Myzus persicae Sulzer and Aphis craccivora Koch. We found two classes of neonicotinoids with distinct modes of interference with [3H]imidacloprid, described as direct competitive inhibition and non-competitive inhibition, respectively. Competitive neonicotinoids were acetamiprid, nitenpyram, thiacloprid, clothianidin and nithiazine, whereas thiamethoxam and the N -methyl analogues of imidacloprid and clothianidin showed non-competitive inhibition. The chloropyridine or chlorothiazole heterocycles, the polar pharmacophore parts, such as nitroimino, cyanoimino and nitromethylene, and the cyclic or acyclic structure of the pharmacophore were not relevant for the mode of inhibition. Consensus structural features of the neonicotinoids were defined for the two mechanisms of interaction with [3H]imidacloprid binding. Furthermore, two sub-classes of non-competitive inhibitors can be discriminated on the basis of their Hill coefficients for imidacloprid displacement. We conclude from the present data that the direct competitors share the binding site with imidacloprid, whereas non-competitive compounds, like thiamethoxam, bind to a different site or in a different mode. Copyright © 2004 Society of Chemical Industry [source] Fullerene derivatives encapsulated in carbon nanotubesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007W. Plank Abstract We report on the preparation and subsequent Raman analysis of carbon nanotube peapods, using the fullerene C60 and its heterofullerene derivative (C59N)2 as filling materials. The filling with (C59N)2 was done from liquid solution at room temperature and from the gas phase at elevated temperatures. The success of the encapsulation procedure is confirmed through the identification of fingerprint Raman modes and the conversion to double wall nanotubes through heating to 1250 °C. The 2D mode of double wall nanotubes made from (C59N)2 peapods is observed to be downshifted compared to the same mode in double wall nanotubes made from C60 peapods. We interpret this downshift as an evidence for the integration of the nitrogen into the lattice of the inner tube. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systemsANNALS OF APPLIED BIOLOGY, Issue 1 2007A. Milne Abstract A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose,response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance. [source] Resistance of insect pests to neonicotinoid insecticides: Current status and future prospects ,ARCHIVES OF INSECT BIOCHEMISTRY AND PHYSIOLOGY (ELECTRONIC), Issue 4 2005Ralf Nauen Abstract The first neonicotinoid insecticide introduced to the market was imidacloprid in 1991 followed by several others belonging to the same chemical class and with the same mode of action. The development of neonicotinoid insecticides has provided growers with invaluable new tools for managing some of the world's most destructive crop pests, primarily those of the order Hemiptera (aphids, whiteflies, and planthoppers) and Coleoptera (beetles), including species with a long history of resistance to earlier-used products. To date, neonicotinoids have proved relatively resilient to the development of resistance, especially when considering aphids such as Myzus persicae and Phorodon humuli. Although the susceptibility of M. persicae may vary up to 20-fold between populations, this does not appear to compromise the field performance of neonicotinoids. Stronger resistance has been confirmed in some populations of the whitefly, Bemisia tabaci, and the Colorado potato beetle, Leptinotarsa decemlineata. Resistance in B- and Q-type B. tabaci appears to be linked to enhanced oxidative detoxification of neonicotinoids due to overexpression of monooxygenases. No evidence for target-site resistance has been found in whiteflies, whereas the possibility of target-site resistance in L. decemlineata is being investigated further. Strategies to combat neonicotinoid resistance must take account of the cross-resistance characteristics of these mechanisms, the ecology of target pests on different host plants, and the implications of increasing diversification of the neonicotinoid market due to a continuing introduction of new molecules. Arch. Insect Biochem. Physiol. 58:200,215, 2005. © 2005 Wiley-Liss, Inc. [source] Trend and variability of China precipitation in spring and summer: linkage to sea-surface temperaturesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2004Fanglin Yang Abstract Observational records in the past 50 years show an upward trend of boreal-summer precipitation over central eastern China and a downward trend over northern China. During boreal spring, the trend is upward over southeastern China and downward over central eastern China. This study explores the forcing mechanism of these trends in association with the global sea-surface temperature (SST) variations on the interannual and interdecadal time scales. Results based on singular value decomposition (SVD) analyses show that the interannual variability of China precipitation in boreal spring and summer can be well defined by two centres of action for each season, which are covarying with two interannual modes of SSTs. The first SVD modes of precipitation in spring and summer, which are centred in southeastern China and northern China respectively, are linked to an El Niño,southern oscillation (ENSO)-like mode of SSTs. The second SVD modes of precipitation in both seasons are confined to central eastern China, and are primarily linked to SST variations over the warm pool and the Indian Ocean. Features of the anomalous 850 hPa winds and 700 hPa geopotential height corresponding to these modes support a physical mechanism that explains the causal links between the modal variations of precipitation and SSTs. On the decadal and longer time scale, similar causal links are found between the same modes of precipitation and SSTs, except for the case of springtime precipitation over central eastern China. For this case, while the interannual mode of precipitation is positively correlated with the interannual variations of SSTs over the warm pool and Indian Ocean, the interdecadal mode is negatively correlated with a different SST mode, i.e. the North Pacific mode. The latter is responsible for the observed downward trend of springtime precipitation over central eastern China. For all other cases, both the interannual and interdecadal variations of precipitation can be explained by the same mode of SSTs. The upward trend of springtime precipitation over southeastern China and downward trend of summertime precipitation over northern China are attributable to the warming trend of the ENSO-like mode. The recent frequent summertime floods over central eastern China are linked to the warming trend of SSTs over the warm pool and Indian Ocean. Copyright © 2004 Royal Meteorological Society [source] | |||||||||||||