Microparticle dispensers for the controlled release of insect pheromones

The potential utility of micrometer-sized particles as controlled-release devices for the volatilization of insect pheromones for mating disruption applications is evaluated in this study for two pheromone/model compound systems (codlemone/1-dodecanol and disparlure/1,2-epoxyoctadecane). To expedite the measurement of release rates from these particle devices, two techniques based on thermogravimetric analysis (TGA) have been exploited: isothermal TGA (I-TGA) at elevated temperatures (40-80 degrees C) with N(2) convection and volatilization temperature (VT) by dynamic TGA. A correlation between these two methods has been established. Samples that exhibit a higher VT provide a lower release rate from a particle substrate. Using these techniques, it has been demonstrated that chemical interactions between adsorbed liquids and particle surfaces may play a small role in defining release characteristics under conditions of low surface area, whereas parameters associated with total surface area and micropore structure appear to be much more significant in retarding evaporation for uncoated particles containing an adsorbed liquid. Additional regulation of release rates was achieved by coating the particle systems with water-soluble or water-dispersible polymers. By careful selection of particle porosity and coating composition, it is envisioned that the evaporation rate of pheromones can be tailored to specific insect control applications.     

Castanea sativa Mill. leaves as new sources of natural antioxidant: an electronic spin resonance study

The antioxidant potential of Castanea sativa Mill. leaf (sweet chestnut) was explored as a new source of active extracts. The capacity of the different fractions issued from aqueous, methanol, and ethyl acetate extracts to inhibit the stable free radical 2,2-diphenyl-1-pycryl-hydrazyl, superoxide anion, and hydroxyl radical was measured by electronic spin resonance. Their scavenging potential was analyzed versus their amount of phenolic compounds. Among the active fractions, the most effective one was A6, an ethyl acetate fraction, which contained a high level of total phenolic compounds (29.1 g/100 g). Thus, a different extraction procedure was performed to concentrate the active compounds of A6 in the new C. sativa leaf extract (CSLE). Compared to reference antioxidants (quercetin and vitamin E) and standard extracts (Pycnogenol, from French Pinus maritima bark, and grape marc extract), it was observed that A6 and CSLE have high antioxidant potentials, equivalent to at least those of reference compounds.     

Effects of accelerators on mobility of 14C-2,4-dichlorophenoxy butyric acid in plant cuticles depends on type and concentration of accelerator

Effects of diethyl suberate (DESU), diethyl sebacate (DES), dibutyl suberate (DBSU), dibutyl sebacate (DBS), and tributyl phosphate (TBP) on diffusion of 14C-2,4-dichlorophenoxy butyric acid (2,4-DB) across cuticular membranes (CM) was studied. Astomatous CM were isolated enzymatically from Stephanotis floribunda Brongn. leaves, and diffusion was measured at 20 degrees C. The alkyl-substituted dicarboxylic acids constitute a homologous series with carbon numbers increasing from C12 to C18. Molecular weights increased only moderately from 230.0 (DESU) to 314.5 (DBS), while partition coefficients varied over orders of magnitude from 92 (DESU), to 1213 (DES), to 15,988 (DBSU), to 210,762 (DBS). All the above compounds turned out to be accelerators as they increased 2,4-DB mobility by up to 40-fold with accelerator concentrations in the CM ranging from only 9.2 to 105 g kg(-1). Efficacy (2,4-DB mobility in the presence/mobility in the absence of accelerators) increased with increasing concentrations of accelerators in CM or in reconstituted cuticular waxes. Plotting efficacy vs accelerator concentration in the CM resulted in straight lines, and their slopes increased in the order DBS (0.14), DBSU (0.31), DES (0.51), and DESU (0.85). Hence, DESU was the most powerful accelerator in this series as it increased 2,4-DB mobility in the CM about 6 times more than DBSU. Waxes constitute the major barrier in plant cuticles, and plots of efficacy vs accelerator concentration in Stephanotis wax were also linear, but compared to CM slopes were steeper by factors of 3.20 (DBS), 2.97 (DBSU), 2.70 (DES), and 1.62 (DESU). TBP was similarly effective as DESU, but plots of efficacy vs concentration were not linear, and curves approached a plateau at 60-80 g kg(-1). These data are discussed with regard to suitability of these accelerators for formulating systemic pesticides.     

Evaluation of the nutritional characteristics of a finger millet based complementary food

Finger millet (Eleusine coracana), kidney beans (Phaseolus vulgaris), peanuts (Arachis hypogoea), and mango (Mangifera indica) were processed separately and then combined, on the basis of their amino acid scores and energy content, into a complementary food for children of weaning age. The finger millet and kidney beans were processed by germination, autoclaving, and lactic acid fermentation. A mixture containing, on a dry matter basis, 65.2, 19.1, 8.0, and 7.7% of the processed finger millet, kidney beans, peanuts, and mango, respectively, gave a composite protein with an in vitro protein digestibility of 90.2% and an amino acid chemical score of 0.84. This mixture had an energy density of 16.3 kJ.g(-1) of dry matter and a decreased antinutrient content and showed a measurable improvement in the in vitro extractability for calcium, iron, and zinc. A 33% (w/v) pap made from a mix of the processed ingredients had an energy density of 5.4 kJ.g(-1) of pap, which is sufficient to meet the energy requirements of well-nourished children of 6-24 months of age at three servings a day and at the FAO average breast-feeding frequency.     

Reliability of an expert-based runoff and erosion model: Application of STREAM to different environments

During the last decades, the European loess belt has been confronted with a significant increase in environmental problems due to erosion on agricultural land. Spatially distributed runoff and erosion models operating at the catchment scale are therefore needed to evaluate the impact of potential mitigation measures. Expert-based models offer an alternative solution to process-based and empirical models, but their decision rules are only valid for the local conditions for which they have been derived. The STREAM model, which was developed in Normandy (France), has been applied in two Belgian catchments having a similar soil texture, as well as in a catchment of southern France differing by soil, land use and climate characteristics. The performance of hydrological models can be assessed for instance by calculating the Nash–Sutcliffe efficiency criterion (E_NS). When applied to Belgium, the model results are satisfactory to good after an adaptation of the decision rules (0.90 < E_NS < 0.93 for runoff predictions and 0.85 < E_NS < 0.89 for erosion predictions). Given the important environmental differences between Normandy and southern France, the model rules were also adapted for application in the latter environment. Unfortunately, the quality of runoff predictions was insufficient to simulate erosion in southern France. In conclusion, STREAM is a reliable model providing satisfactory runoff and erosion predictions in the regions where hortonian overland flow dominates. Nevertheless, an adaptation of decision rules based on local multi-scale (plot, field, catchment) data is needed, before running the model. STREAM can then serve as a decision support tool to design for instance flood control measures.     

Differential resistance of switchgrass <Emphasis Type="Italic">Panicum virgatum</Emphasis> L. lines to fall armyworms <Emphasis Type="Italic">Spodoptera frugiperda</Emphasis> (J. E. Smith)

Six cultivars of switchgrass Panicum virgatum L., a plant native to North America that has potential as a bioenergy source, were evaluated for resistance to feeding by the fall armyworm Spodoptera frugiperda (J. E. Smith). Although no mortality was noted, seedlings of the cultivar ‘Trailblazer’ and older plants of the cultivar ‘Blackwell’ were among the most resistant to feeding by S. frugiperda. Some field-collected samples from natural habitat were fed upon by S. frugiperda as readily as were the cultivars, while others caused high mortality after 2 days. Enzyme assays indicated relative differences in expression of two peroxidases thought to be involved in insect resistance in maize, but not in two chitinolytic enzymes. Genomic searches based on maize-sequence templates for the aforementioned genes identified homologs in switchgrass. Sequencing of cDNA coding for these genes identified some differences, especially in the cationic peroxidase, which could influence relative activity. These results indicate switchgrass germplasm has varying resistance to fall armyworms which could be a function of gene sequence diversity, as well as of variation in gene expression due to differences in ploidy levels or other factors.     

Nutrient limitations to bacterial and fungal growth during cellulose decomposition in tropical forest soils

Nutrients constrain the soil carbon cycle in tropical forests, but we lack knowledge on how these constraints vary within the soil microbial community. Here, we used in situ fertilization in a montane tropical forest and in two lowland tropical forests on contrasting soil types to test the principal hypothesis that there are different nutrient constraints to different groups of microorganisms during the decomposition of cellulose. We also tested the hypotheses that decomposers shift from nitrogen to phosphorus constraints from montane to lowland forests, respectively, and are further constrained by potassium and sodium deficiency in the western Amazon. Cellulose and nutrients (nitrogen, phosphorus, potassium, sodium, and combined) were added to soils in situ, and microbial growth on cellulose (phospholipid fatty acids and ergosterol) and respiration were measured. Microbial growth on cellulose after single nutrient additions was highest following nitrogen addition for fungi, suggesting nitrogen as the primary limiting nutrient for cellulose decomposition. This was observed at all sites, with no clear shift in nutrient constraints to decomposition between lowland and montane sites. We also observed positive respiration and fungal growth responses to sodium and potassium addition at one of the lowland sites. However, when phosphorus was added, and especially when added in combination with other nutrients, bacterial growth was highest, suggesting that bacteria out-compete fungi for nitrogen where phosphorus is abundant. In summary, nitrogen constrains fungal growth and cellulose decomposition in both lowland and montane tropical forest soils, but additional nutrients may also be of critical importance in determining the balance between fungal and bacterial decomposition of cellulose.     

Environmental effects on soil NO concentrations and root N uptake in beech and spruce forests

This study aimed to investigate the shifts in net nitrogen (N) uptake and N compounds of fine roots over the vegetation period (i.e., spring, summer, autumn) and correlate this with NO concentration in the soil. Soil NO concentration was measured using gas lysimeters for collection and a chemiluminescence analyzer for quantification. Net N uptake by the roots was determined using the ¹⁵N enrichment technique. N pools were quantified using spectrophotometric techniques. Soil NO concentrations at beech and spruce forest sites were highest in spring (June), and lowest in winter (December). Total N of the roots was similar during the seasons and between the two years under study despite considerable variation of different N compounds. Net N uptake generally increased with higher N supply. Correlation analysis revealed a positive relationship between soil NO concentration and net N uptake only for spruce trees. This relationship seemed to be modulated by environmental factors and tree species.     

Factors influencing the survivorship of the burrowing nematode,Radopholus similis (Cobb.) Thorne in two types of soil from banana plantations in Martinique

The burrowing nematode, Radopholus similis (Cobb.) Thorne, causes the most damage to bananas. To minimize nematicide applications, cropping systems that use fallow, crop rotation and clean planting material have been developed in the French West Indies. In order to optimize the benefit of the intercropping period, we studied the survivorship of R. similis in different soil types and conditions. We monitored the survivorship of calibrated populations of R. similis in the laboratory on a Nitisol and on an Andosol, two soils derived from volcanic ashes and pumices. We studied water potentials ranging from 0 to ?700 kPa on undisturbed soil and on soil previously frozen to get rid of living nematodes. Mortality of adult R. similis decreased regularly, and was fairly well described by Teissier's model. In the previously frozen soils, R. similis survived longer in wet soils (half-life of 21–46 days at 0 to ?5 kPa) than in dry soils (half-life of less than 10 days between ?80 and ?250 kPa). In contrast, in undisturbed soils, R. similis survived longer in dry soils: half-lives ranged from 57 days at ?273 kPa to 17 days at water saturation in the Andosol, and 36 days at ?660 kPa to 14 days at water saturation in the Nitisol. These results are consistent with the absence of anhydrobiosis in R. similis, unlike Pratylenchus coffeae. P. coffeae survivorship curves over time do not follow a model derived from exponential decrease like Teissier's model. These results also show that the recommended one year host-free period required to sanitize soils cannot be shortened without risk, even if flooding the soil could improve it.