Soil genesis and heterogeneity of phosphorus forms and carbon below mounds inhabited by primary and secondary termites

Termite activities are known to significantly influence small-scale soil properties in tropical savannas. The lateral and vertical extent of the alterations to the nest's surrounding, and particularly resulting impacts on diagnostic soil horizons remain largely unresolved until today. We examined the effects of mound-building termites on soil genesis and constitutive chemical soil properties in and below their nests. Two transects to a soil depth of 100 cm were dug below three younger mounds of Cornitermes silvestrii (the primary nest builder), three older mounds in which C. silvestrii had died out and which were secondarily colonized mainly by Nasutitermes kemneri, and three reference sites in the Brazilian Cerrado. The samples were characterized by standard procedures for soil classification; in addition, phosphorus extractions were conducted on selected samples using NaHCO₃ for labile P forms, and concentrated HCl for stable P forms. This data set was then used to build calibration models for the prediction of labile and stable inorganic (P_i) and organic (P_o) P forms, as well as for contents of organic carbon (OC), for the remaining samples applying mid-infrared spectroscopy in combination with partial least squares regression (MIRS-PLSR). We can show that the termite influence on the soil was sufficiently large to change diagnostic characteristics of the soils under termite mounds. The MIRS-PLSR predictions were suitable for quantifying organic carbon and most of the labile and stable phosphorus fractions. They showed an enrichment of OC, NaHCO₃-P_o and NaHCO₃-P_i contents in nests inhabited by primary and secondary termites by factors of 1.6–2.0 and 1.4–1.5, respectively. The soils surrounding the nests had higher contents of OC and NaHCO₃-P under both nest types vertically down to 30 cm below the lower nest border, and OC and NaHCO₃-P_i contents were elevated at minimum to a lateral distance of 60 cm away from the nest border. As the pattern of HCl_conc-P_i, which comprised 95% of total P, showed no variations, we conclude that the higher NaHCO₃-P_i amount was formed in termite nests by changing the availability of the more stable HCl_conc-P_i. In contrast to the contents, the OC and NaHCO₃-P stocks below the mounds inhabited by primary termites were comparable to those inhabited by secondary ones, because the bulk density of the secondarily inhabited nests was elevated. This was due to a transport of clay-rich material from the subsurface argic horizons into the nests. Here, the secondary termites even reverted the lessivation observed in the reference soils and under mounds inhabited by primary termites, thus causing the soil types to change from Alisols and Acrisols to the properties of Umbrisols.     

Reversing agriculture from intensive to sustainable improves soil quality in a semiarid South Italian soil

Intensive agriculture (IA) is widespread in South Italy, although it requires frequent tillage, large amounts of fertilizers and irrigation water. We have assessed the efficacy of reversing IA to sustainable agriculture (SA) in recovering quality of a typical South Italy soil (Lithic Haploxeralf). This reversion, lasting from 2000 to 2007, replaced 75% of nutrients formerly supplied inorganically by farmyard manuring and reduced the tillage frequency. Several chemical and biochemical properties, functionally related to C and N mineralisation–immobilisation processes and to P and S nutrient cycles, were monitored annually from 2005 to 2007 in the spring. Reversing IA to SA decreased soil bulk density, almost doubled the soil organic matter (SOM) as favoured the immobilisation of C and N, increased most soil microbial indicators but decreased contents of nitrate, mineral N and K₂SO₄-extractable C. The K₂SO₄-extractable C/K₂SO₄-extractable organic N ratio suggested that substrate quality rather than the mass of readily available C and N affected biomass and activity of soil microflora. Also, the largely higher 10-day-evolved CO₂–C-to-inorganic N ratio under SA than IA indicated that higher C mineralisation, associated with higher microbial biomass N immobilisation, occurred under SA than IA. Decreases in most soil enzyme activities under IA, compared to SA, were much higher than concomitant decreases in SOM content. Soil salinity and sodicity were always higher in IA than SA soil, although not critically high, likely due to the intensive inorganic fertilisation as irrigation waters were qualitatively and quantitatively the same between the two soils. Thus, we suggest that the cumulative small but long-term saline (osmotic) and sodic (dispersing) effects in IA soil decreased the microbial variables more than total organic C and increased soil bulk density.     

Reconstruction of Microraptor and the evolution of iridescent plumage

Iridescent feather colors involved in displays of many extant birds are produced by nanoscale arrays of melanin-containing organelles (melanosomes). Data relevant to the evolution of these colors and the properties of melanosomes involved in their generation have been limited. A data set sampling variables of extant avian melanosomes reveals that those forming most iridescent arrays are distinctly narrow. Quantitative comparison of these data with melanosome imprints densely sampled from a previously unknown specimen of the Early Cretaceous feathered Microraptor predicts that its plumage was predominantly iridescent. The capacity for simple iridescent arrays is thus minimally inferred in paravian dinosaurs. This finding and estimation of Microraptor feathering consistent with an ornamental function for the tail suggest a centrality for signaling in early evolution of plumage and feather color.     

Controlled-release systems for the delivery of cyromazine into water surface

Controlled-release systems (CRSs) for the insect growth regulator cyromazine (Neporex), as a larvicide against Culex pipiens (Culicidae) mosquitoes, are under development. Despite promising results obtained previously for both in vitro (dissolution tests) and in vivo systems (mosquito larvae floating on water surfaces), it was evident that the CRSs did not remain afloat for sufficiently long times. The present study was thus conducted to determine the relationship between the process parameters and the potential contact time of the active ingredient with the mosquito larvae. A series of CRSs were prepared by an extrusion process, alone or in combination with a supplementary coating. The active ingredient was incorporated into the matrix or the coating. The matrix comprised low-density polyethylene 600 and perlite, and the coating, a polyurea with or without the addition of paraffin wax. The study showed that the cumulative release of the active ingredient into water could be controlled by manipulating the preparation techniques, the types and concentrations of inert materials, and the concentration of the active ingredient.     

Engineering modified Bt toxins to counter insect resistance

The evolution of insect resistance threatens the effectiveness of Bacillus thuringiensis (Bt) toxins that are widely used in sprays and transgenic crops. Resistance to Bt toxins in some insects is linked with mutations that disrupt a toxin-binding cadherin protein. We show that susceptibility to the Bt toxin Cry1Ab was reduced by cadherin gene silencing with RNA interference in Manduca sexta, confirming cadherin's role in Bt toxicity. Native Cry1A toxins required cadherin to form oligomers, but modified Cry1A toxins lacking one alpha-helix did not. The modified toxins killed cadherin-silenced M. sexta and Bt-resistant Pectinophora gossypiella that had cadherin deletion mutations. Our findings suggest that cadherin promotes Bt toxicity by facilitating toxin oligomerization and demonstrate that the modified Bt toxins may be useful against pests resistant to standard Bt toxins.     

Glial membranes at the node of Ranvier prevent neurite outgrowth

Nodes of Ranvier are regularly placed, nonmyelinated axon segments along myelinated nerves. Here we show that nodal membranes isolated from the central nervous system (CNS) of mammals restricted neurite outgrowth of cultured neurons. Proteomic analysis of these membranes revealed several inhibitors of neurite outgrowth, including the oligodendrocyte myelin glycoprotein (OMgp). In rat spinal cord, OMgp was not localized to compact myelin, as previously thought, but to oligodendroglia-like cells, whose processes converge to form a ring that completely encircles the nodes. In OMgp-null mice, CNS nodes were abnormally wide and collateral sprouting was observed. Nodal ensheathment in the CNS may stabilize the node and prevent axonal sprouting.     

Propolis extract combined with oregano essential oil applied to lima bean seeds against Sclerotinia sclerotiorum

European Journal of Plant Pathology - In this study, propolis extract (EPE) and oregano essential oil (OEO), both natural products with different bioactive compounds, were evaluated in vitro and in...     

Composition and anti-insect activity of essential oils from Tagetes L. species (Asteraceae, Helenieae) on Ceratitis capitata Wiedemann and Triatoma infestans Klug

Essential oils from four species of the genus Tagetes L. (Asteraceae, Helenieae) collected in Tucuma?n province, Argentina, were evaluated for their chemical composition, toxicity, and olfactory activity on Mediterranean fruit fly Ceratitis capitata Wiedemann adults and for repellent properties on Triatoma infestans (Klug) (Chagas disease vector). Yields of essential oils range from 0.2 to 0.8% (v/w). The same main constituents among Tagetes minuta L., Tagestes rupestris Cabrera, and Tagetes terniflora Kunth, (cis-trans)-ocimenes, (cis-trans)-tagetones, and (cis-trans)-ocimenones showed important differences in their relative compositions. Tagetes filifolia Lag. was characterized by the recognized phenylpropanoids methylchavicol and trans-anethole as the main components. LD(50) was ≤20 μg/insect in topical bioassays. T. rupestris was the most toxic to C. capitata females, whereas the other oils presented similar toxicities against males and females. Tagetes rupestris oil attracted both sexes of C. capitata at 5 μg, whereas T. minuta showed opposite activities between males (attractant) and females (repellent). Oils from T. minuta and T. filifolia were the most repellent to T. infestans. The results suggest that compositions of essential oils influence their insecticidal and olfactory properties. The essential oils from Tagetes species show an important potential as infochemical agents on insects' behaviors. This study highlights the chemical variability of essential oils as a source of variation of anti-insect properties.