Toxicity and behavioral effects of nootkatone, 1,10-dihydronootkatone, and tetrahydronootkatone to the formosan subterranean termite (Isoptera: Rhinotermitidae)

Toxicity and behavioral effects of nootkatone and two of its derivatives, 1,10-dihydronootkatone and tetrahydronootkatone, to Coptotermes formosanus Shiraki were investigated on workers from two different colonies by using topical application assays, repellency assays, and sand barrier assays. The acute toxicity of the nootkatones on workers from both colonies increased as the saturation of the molecule increased, but the difference was significant for only one colony. The results of the repellency assays showed a similar trend of efficiency; the threshold concentration for significant repellency was four-fold higher in nootkatone treatments (50 ppm) than in the reduced derivatives 1,10-dihydronootkatone or tetrahydronootkatone (12.5 ppm). In sand barrier assays, a concentration of 100 ppm of any of the three chemicals significantly reduced termite survival, tunnel building, and food consumption after a 12-d exposure. Termites preexposed tolOO ppm nootkatone-treated sand and placed in containers without nootkatone for 15 d continued to exhibit abnormal feeding and digging behaviors; survivorship, tunneling, and feeding activities were significantly reduced by 83.5, 63.2, and 95.4%, respectively. Termites pretreated for 12 d at concentrations of 50 and 75 ppm nootkatone and tetrahydronootkatone returned to normal digging activity after they were removed from the treatments, but their feeding activity was significantly reduced

What is the Oxygen Isotope Composition of Venus? The Scientific Case for Sample Return from Earth’s “Sister” Planet

Venus is Earth’s closest planetary neighbour and both bodies are of similar size and mass. As a consequence, Venus is often described as Earth’s sister planet. But the two worlds have followed very different evolutionary paths, with Earth having benign surface conditions, whereas Venus has a surface temperature of 464 °C and a surface pressure of 92 bar. These inhospitable surface conditions may partially explain why there has been such a dearth of space missions to Venus in recent years.The oxygen isotope composition of Venus is currently unknown. However, this single measurement (Δ17O) would have first order implications for our understanding of how large terrestrial planets are built. Recent isotopic studies indicate that the Solar System is bimodal in composition, divided into a carbonaceous chondrite (CC) group and a non-carbonaceous (NC) group. The CC group probably originated in the outer Solar System and the NC group in the inner Solar System. Venus comprises 41% by mass of the inner Solar System compared to 50% for Earth and only 5% for Mars. Models for building large terrestrial planets, such as Earth and Venus, would be significantly improved by a determination of the Δ17O composition of a returned sample from Venus. This measurement would help constrain the extent of early inner Solar System isotopic homogenisation and help to identify whether the feeding zones of the terrestrial planets were narrow or wide.Determining the Δ17O composition of Venus would also have significant implications for our understanding of how the Moon formed. Recent lunar formation models invoke a high energy impact between the proto-Earth and an inner Solar System-derived impactor body, Theia. The close isotopic similarity between the Earth and Moon is explained by these models as being a consequence of high-temperature, post-impact mixing. However, if Earth and Venus proved to be isotopic clones with respect to Δ17O, this would favour the classic, lower energy, giant impact scenario.We review the surface geology of Venus with the aim of identifying potential terrains that could be targeted by a robotic sample return mission. While the potentially ancient tessera terrains would be of great scientific interest, the need to minimise the influence of venusian weathering favours the sampling of young basaltic plains. In terms of a nominal sample mass, 10 g would be sufficient to undertake a full range of geochemical, isotopic and dating studies. However, it is important that additional material is collected as a legacy sample. As a consequence, a returned sample mass of at least 100 g should be recovered.Two scenarios for robotic sample return missions from Venus are presented, based on previous mission proposals. The most cost effective approach involves a “Grab and Go” strategy, either using a lander and separate orbiter, or possibly just a stand-alone lander. Sample return could also be achieved as part of a more ambitious, extended mission to study the venusian atmosphere. In both scenarios it is critical to obtain a surface atmospheric sample to define the extent of atmosphere-lithosphere oxygen isotopic disequilibrium. Surface sampling would be carried out by multiple techniques (drill, scoop, “vacuum-cleaner” device) to ensure success. Surface operations would take no longer than one hour.Analysis of returned samples would provide a firm basis for assessing similarities and differences between the evolution of Venus, Earth, Mars and smaller bodies such as Vesta. The Solar System provides an important case study in how two almost identical bodies, Earth and Venus, could have had such a divergent evolution. Finally, Venus, with its runaway greenhouse atmosphere, may provide data relevant to the understanding of similar less extreme processes on Earth. Venus is Earth’s planetary twin and deserves to be better studied and understood. In a wider context, analysis of returned samples from Venus would provide data relevant to the study of exoplanetary systems

Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

Evaluation of Vetiver Grass Root Growth, Oil Distribution, and Repellency Against Formosan Subterranean Termites

The growth rate of vetiver grass [Vetiveria zizanioides (L.) Nash (Graminales: Poaceae)], roots, and oil distribution were evaluated in an 8-month field study. The amount of vetiver oil present in the root system increased with each sampling date. In December, the final sampling period, mean root weight increased 520% from the previous sampling period (October). At the end of the study, root growth measured over 2 m long and 25 cm wide and weighed 0.48 kg (dry weight). In addition, a laboratory study was conducted to determine if the roots of vetiver grass when used as mulch, are effective against Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). In past studies, chemical components in the roots of this grass were shown to be effective repellents and toxicants to Formosan subterranean termites. In the present study, the 25% vetiver root mulch treatment proved to decrease tunneling activity and wood consumption and increase termite mortality. These results provide preliminary evidence that vetiver roots may have use as an additive to garden mulches against termites

Terpene-lnduced Morphological Changes to Exoskeleton of Formosan Subterranean Termites (Isoptera: Rhinotermitidae): Toxic Effects of cis-nerol

The terpenoid, cis-nerol was found to be highly toxic to the Formosan subterranean termite, Coptotermes formosanus Shiraki. Morphological abnormalities were observed in the exoskeleton including the spiracles and trichoid sensilla using scanning electron microscopy after exposure of termites to cis-nerol for 2 h. Proteins were found in a water-soluble fraction collected from the whole termite body exposed to cis-nerol for 60 min. It appears that terpenoids cause damage to cell membranes resulting in a significant loss of proteins

Direct Physical Evidence of Dolomite Recrystallization

The possibility of recrystallization is a long-standing barrier to deciphering the genetic origin of dolomites. There is often uncertainty regarding whether or not characteristics of ancient dolomites are primary or the consequence of later recrystallization unrelated to the original dolomitization event. Results from 65 new high-temperature dolomite synthesis experiments (1 M, 1_0 Mg/ Ca ratio solutions at 218°C) demonstrate dolomite recrystallization affecting stoichiometry, cation ordering and nanometre-scale surface texture. The data support a model of dolomitization that proceeds by a series of four unique phases of replacement and recrystallization, which occur by various dissolution– precipitation reactions. During the first phase (induction period), no dolomite forms despite favourable conditions. The second phase (replacement period) occurs when Ca-rich dolomite products, with a low degree of cation ordering, rapidly replace calcite reactants. During the replacement period, dolomite stoichiometry and the degree of cation ordering remain constant, and all dolomite crystal surfaces are covered by nanometre-scale growth mounds. The third phase (primary recrystallization period), which occurs in the experiments between 97% and 100% dolomite, is characterized by a reduced replacement rate but concurrent increases in dolomite stoichiometry and cation ordering. The end of the primary recrystallization period is marked by dolomite crystal growth surfaces that are covered by flat, laterally extensive layers. The fourth phase of the reaction (secondary recrystallization period) occurs when all calcite is consumed and is characterized by stoichiometric dolomite with layers as well as a continued increase in the degree of cation ordering with time. Inferences of recrystallization, in natural dolomite, based on cation order or stoichiometry of dolomite, usually depend on assumptions about the precursor dolomite subjected to recrystallization. If it is assumed that the experimental evidence presented here is applicable to natural, low-temperature dolomites, then the presence of mounds is direct evidence of a lack of recrystallization and the presence of layers is direct evidence of recrystallization

Effect of magnetic interactions and multiple magnetic phases on the giant magnetoresistance of heterogeneous cobalt-silver films

URL: http://www-spht.cea.fr/articles/s94/018International audienceWe have observed magnetic and electrical transport properties in giant magnetoresistive inhomogeneous cobalt-silver films. The material consists of two distinct magnetic phases: large clusters which dominate the magnetization and magnetoresistive processes at room temperature, between which cooperative behavior is observed; and small clusters which dominate the magnetization below 10\nobreak\ K, but make only a minor contribution to the magnetoresistance. Both the variation of the magnetoresistance with magnetization in the film and the difference in the magnetoresistance between the zero-field-cooled and field-cycled state are interpreted by invoking interactions between the active magnetic regions in the sample