Comparison of gravimetry and planimetry in determining dry matter budgets for three species of phytophagous lepidopteran larvae

Gravimetric and a combination areal-gravimetric methods for determining dry matter budgets for leaf eating Lepidoptera were compared. The gravimetric method is based on dry weight/live weight ratios of the leaves fed to the larvae. In the areal-gravimetric method, the quantity of food offered to the larvae is determined from the area of leaf tracings and the dry matter content per unit area of the leaves. The areal-gravimetric method permits the use of larger leaf sprays and an open, gauze enclosed rearing chamber. There were no consistent differences in budget factors (growth, ingestion or egestion), nor were there any differences in the observed variability of the data attributable to the method used. However, the expected variability based on instrument precision for the gravimetric method is less than for the areal-gravimetric method. Experimental factors inherent in the gravimetric method introduce variability to the measurements that are not present in the areal method. Thirty to 60% of the variability in budget factors was attributed to intrinsic properties of the larvae, even though the larvae were taken from the same egg masses.

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Résumé Les budgets en matière sèche consommée par des lépidoptères ont été comparés par les méthodes gravimétrique et planimétrique. La méthode gravimétrique est basée sur le rapport poids sec/poids frais de feuilles consommées par les chenilles. Avec la méthode planimétrique, la quantité d'aliment proposée aux chenilles est déterminée par les tracés de la surface des feuilles et le contenu de matière sèche par unité de surface des feuilles. La méthode de planimétrie permet l'utilisation de plus grands rameaux de feuilles et de cages d'élevage extérieures en gaze. Il n'y avait pas de différence appréciable dans les éléments du budget (croissance, ingestion et déjection), ni aucune différence dans la variabilité observée des données attribuable à la méthode utilisée. Cependant, la variabilité attendue d'après la précision des mesures avec la méthode gravimétrique est inférieure à celle de la méthode planimétrique. est inférieure à celle de la méthode planimétrique. Des éléments expérimentaux, inhérents à la méthode gravimétrique, introduisent une variabilité dans les mesures que l'on n'a pas avec la méthode planimétrique. 30–60% de la variabilité dans la consommation ont été attribués à des paramètres internes à la chenille, même quand elles provenaient toutes de la même ooplaque.

     

Effect of a Bacillus subtilis strain on flax protection against Fusarium oxysporum and its impact on the root and stem cell walls

In Normandy, flax is a plant of important economic interest because of its fibres. Fusarium oxysporum, a telluric fungus, is responsible for the major losses in crop yield and fibre quality. Several methods are currently used to limit the use of phytochemicals on crops. One of them is the use of plant growth promoting rhizobacteria (PGPR) occurring naturally in the rhizosphere. PGPR are known to act as local antagonists to soil‐borne pathogens and to enhance plant resistance by eliciting the induced systemic resistance (ISR). In this study, we first investigated the cell wall modifications occurring in roots and stems after inoculation with the fungus in two flax varieties. First, we showed that both varieties displayed different cell wall organization and that rapid modifications occurred in roots and stems after inoculation. Then, we demonstrated the efficiency of a Bacillus subtilis strain to limit Fusarium wilt on both varieties with a better efficiency for one of them. Finally, thermo‐gravimetry was used to highlight that B. subtilis induced modifications of the stem properties, supporting a reinforcement of the cell walls. Our findings suggest that the efficiency and the mode of action of the PGPR B. subtilis is likely to be flax variety dependent.     

Initial stages of lichen hydration observed by proton magnetic relaxation

The hydration of selected lichens ( Cladonia mitis , Cladonia bellidiflora , Cetraria islandica , Parmelia saxatilis , and Xanthoria parietina ) was investigated using gravimetry and proton magnetic free induction decays (FIDs).
The hydration from gaseous phase and dehydration to gaseous phase showed first-order kinetics. The amount of water which was non-removable in the air-dry state (relative humidity p / p ₀=9%) did not depend significantly on the lichen species and was found to be 5·6±1·0% of the d. wt.
The proton FID Gaussian component from the solid matrix of thallus structure, and two (or, depending on lichen species, one averaged) liquid signals coming from water tightly bound on the surface of thallus solid matrix and from loosely bound or free water, were recorded. The bound-water component was distinguished by its motional properties and by its proximity to endogenous paramagnetic centres present in solid matrix (presumably PS II reaction centres of the photobiont). Mild dehydration (from gaseous phase) could completely remove the loosely bound water fraction, leaving the system below the water percolation threshold and below the water clustering point, emphasizing the passivity of lichen response to desiccation shock. In the species in which the one average liquid component was recorded, bound water behaved similarly.
The hydration at which free water pool vanishes (Δ M / m ₀) and the relative (scaled to water) proton densities of solid matrix of lichen (β) were evaluated for all lichens investigated.     

Prediction of the glass transition temperature of water solutions: comparison of different models

The glass transition temperature (Tg) of a sample is an important parameter that determines its stability during storage. While Tg can be measured by a variety of methods, it is a time-consuming procedure, especially if the sample is to be kept at subzero temperatures, in anhydrous conditions, or if sampling a portion of the specimen for analysis is cumbersome. Hence, predicting rather than directly measuring Tg as a function of the content of the constituents of a blend, mixture, or solution can be a powerful tool. Two main models for predicting Tg have been proposed: Couchman-Karasz (C-K) and Gordon-Taylor (G-T) formalisms. However, many aspects of both are theoretical/terminological in nature, and substantial controversy exists about the various experimental approaches to measuring Tg as well. Here, we compare C-K and G-T formalisms, as well as related problems that arise from the variety of definitions and methods of measuring Tg. Water-trehalose solutions are used as an example for application of the analysis. However, the same conclusions can be expanded to any other solutions so thermodynamical parameters (Tg, DeltaCp, and k) of 20 other commonly used solutes are provided. Practical pitfalls related to determining water content, including experimental data on thermal gravimetry, are also discussed.