Short-range attraction and oviposition stimulant of a biocontrol agent, Galerucella placida Baly (Coleoptera: Chrysomelidae) toward weed leaf surface waxes

Two Polygonaceae weeds, Rumex dentatus L. and Polygonum glabrum Willd. are abundant in wheat- and rice-fields, respectively, in India. Galerucella placida Baly (Coleoptera: Chrysomelidae) is a biocontrol agent of these two weeds. The importance of long-chain alkanes and free fatty acids present in leaf surface waxes of these weeds was assessed as short-range attractant and ovipositional stimulant in G. placida females. Extraction, TLC, GC-MS and GC-FID analyses demonstrated 19 n-alkanes from n-C14 to n-C35 and 14 free fatty acids from C12:0 to C22:0 in leaf surface waxes. Hentriacontane was predominant among alkanes in both weeds, while oleic acid and docosanoic acid were predominant among free fatty acids in R. dentatus and P. glabrum, respectively. Females of G. placida were attracted toward one leaf equivalent surface wax of both weeds against the control solvent (petroleum ether) in a short Y-tube olfactometer bioassay. But, the insect could not differentiate between one leaf equivalent surface wax of R. dentatus and P. glabrum, indicating that both weed leaves were equally attractive in females. A synthetic blend of either 2.44, 35.57 and 23.58 μg ml−1 of octadecane, heptacosane and nonacosane, respectively, resembling the amounts present in one leaf equivalent surface wax of R. dentatus or 4.08, 19.54 and 23.58 μg ml−1 of octadecane, palmitoleic acid and docosanoic acid, respectively, resembling the amounts present in one leaf equivalent surface wax of P. glabrum acted as short-range attractant and ovipositional stimulant in G. placida. These results could be a basis for host plant specificity of the biocontrol agent.

Interrelation between Surface Wax Alkanes from Red Kidney Bean (Phaseolus vulgaris L.) Seeds and Adzuki Bean Weevil [Callosobruchus chinensis (F.)] (Coleoptera: Bruchidae)

Background: Callosobruchus chinensis (Fabricius) (Coleoptera: Bruchidae) is one of the major insect pests of Phaseolus vulgaris L. grains, commonly known as rajma seeds, in Europe and Asia including India. Infestations of these insects destroy majority of legume seeds including rajma which causes a great economic loss. Hence, a proper sustainable pest management measures are necessary for storage of rajma seeds. For this, the study aims to identify and quantify the n-alkane profile from the surface waxes of rajma seeds and their role as olfactory cue in C. chinensis. Individual synthetic alkane followed by the synthetic blends mimicking rajma seed surface wax n-alkanes as olfactory cue was also evaluated.Methods: Collected rajma seeds were solvent extracted to isolate surface waxes. The extract then fractioned by thin-layer chromatography and followed by gas chromatography-mass spectrometry analyses to purify, quantify and identify n-alkanes.Result: Rajma seeds’ surface waxes analysis revealed 18 n-alkanes between n-C15 and n-C33. The predominant alkanes were n-octacosane and n-hexadecane. n-Octadecane was the least abundant alkane in seeds. Total alkane content was 3502.67±12.82µg from 100 g (number 200 ± 5.13) seeds. Adult female C. chinensis elicited attraction towards the surface wax alkanes at concentrations of 0.5, 1, 2, 4 and 6 seed(s) equivalent of rajma seed(s) in the Y-tube olfactometer bioassay, but the highest attraction was observed at 6 seeds equivalent. Hence, a synthetic alkane blend resembling of 6 seeds equivalent, present in seeds’ surface wax alkane or a combination of nine (which elicited positive response) synthetic alkane blend resembling 6 seeds equivalent could be used as lures in developing baited trap in insect pest management programme.

Tribological Properties of Wax on Different Trees Leaf Surface Containing Different Chemical Components

Three kinds of leaf-surface waxes were extracted from different trees, and their chemical compositions were analyzed by Gas Chromatography-Mass Spectrometer (GC-MS). A MFT-R4000 tester was employed to investigate the tribological performances of samples, and the Scanning Electron Microscope (SEM) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were used to characterize the morphologies and chemical compositions on the worn surfaces, respectively. The result showed that waxes can effectively improve the friction reduction and anti-wear abilities of base oil, and different composition of waxes have different improve degree. This can be attributed to the chemical compositions and degree of chemical action.

Spider viscid silk sticks better to superhydrophobic surfaces

ABSTRACTIn a likely coevolutionary arms race, insects evolved a variety of counter strategies to avoid capture by spider webs, while spiders’ evolved innovations web structure and especially their adhesive silks. For instance, insects’ cuticles employ a variety of potential anti-adhesion mechanisms such as the detachable scales of moths and surface waxes and superhydrophobic structures that might resist spreading of glues. In contrast, the viscid capture threads of most spider orb webs are covered with aggregate glue droplets that absorb atmospheric water, tuning glue viscosity to balance the competing demands of surface spreading versus maintaining strong bulk cohesion. Here, we test the hypothesis that superhydrophobicity in insects acts as an anti-adhesion defense against spider silk. We used lotus leaves as a model substrate because its superhydrophobicity outperforms most known insect surfaces. The adhesion of spider capture silk from the web of Larinioides cornutus was studied against three substrates: raw lotus leaves, oxygen plasma treated lotus leaves (hydrophilic lotus), and smooth glass, differing in roughness and chemistry. We found that spider capture silk sticks better to the superhydrophobic lotus than to other surfaces. Both chemistry and physical properties of the leaves contribute to higher adhesion, as raw lotus showed a mean increase in adhesion of 74 % compared to glass, while the similar surface roughness of the hydrophilic lotus increased adhesion by 64 % compared to glass. Thus, evolving a hydrophobic cuticle is unlikely to be a defensive trait used to mitigate the effectiveness of spider webs.

A comparative study on tribological properties of leaf-surface waxes extracted from coastal and inland plants

Purpose This paper aims to explore the leaf-surface wax as green lubricant additive and compare the tribological properties between coastal and inland leaf-surface waxes of the same species plant. Design/methodology/approach The leaf-surface waxes were extracted from the leaves of Robinia pseudoacacia cv. Idaho and Populus nigra in coastal and inland areas, and then the compositions of the four kinds of leaf-surface waxes were characterized using a gas chromatography–mass spectrometry. The tribological properties of these leaf-surface waxes as lubricant additives in the base oil of synthetic ester (SE) were investigated by an MFT-R4000 reciprocating friction and wear tester. As well as the surface morphologies and chemical compositions of the wear scars were characterized by a scanning electron microscope and time-of-flight secondary ion mass spectrometry, respectively. Findings The results indicate that all the leaf-surface waxes as additives can effectively improve the friction reduction and anti-wear performances of SE for steel–aluminum friction pairs. Therein, coastal leaf-surface waxes have better tribological performances than inland leaf-surface waxes, which are attributed to that the leaf-surface waxes extracted from coastal plants can form a better protective film on the worn surface throughout the friction process. Originality/value This paper investigated a new kind of environmentally friendly lubricant additive and compared the tribological properties of the leaf-surface wax extracted from coastal and inland plants. The associated conclusions can provide a reference to explore the tribological performances of leaf-surface wax as green lubricant additive.

A novel maize gene, glossy6 involved in epicuticular wax deposition and drought tolerance

SUMMARYEpicuticular waxes, long-chain hydrocarbon compounds, form the outermost layer of plant surfaces in most terrestrial plants. The presence of epicuticular waxes protects plants from water loss and other environmental stresses. Cloning and characterization of genes involved in the regulation, biosynthesis, and extracellular transport of epicuticular waxes on to the surface of epidermal cells have revealed the molecular basis of epicuticular wax accumulation. However, intracellular trafficking of synthesized waxes to the plasma membrane for cellular secretion is poorly understood. Here, we characterized a maize glossy (gl6) mutant that exhibited decreased epicuticular wax load, increased cuticle permeability, and reduced seedling drought tolerance relative to wild type. We combined an RNA-sequencing based mapping approach (BSR-Seq) and chromosome walking to identify the gl6 candidate gene, which was confirmed via the analysis of multiple independent mutant alleles. The gl6 gene represents a novel maize glossy gene containing a conserved, but uncharacterized domain. Functional characterization suggests that the GL6 protein may be involved in the intracellular trafficking of epicuticular waxes, opening a door to elucidating the poorly understood process by which epicuticular wax is transported from its site of biosynthesis to the plasma membrane.SIGNIFICANCE STATEMENTPlant surface waxes provide an essential protective barrier for terrestrial plants. Understanding the composition and physiological functions of surface waxes, as well as the molecular basis underlying wax accumulation on plant surfaces provides opportunities for the genetic optimization of this protective layer. Genetic studies have identified genes involved in wax biosynthesis, extracellular transport, as well as spatial and temporal regulation of wax accumulation. In this study, a maize mutant, gl6 was characterized that exhibited reduced wax load on plant surfaces, increased water losses, and reduced seedling drought tolerance compared to wild type controls. The gl6 gene is a novel gene harboring a conserved domain with an unknown function. Quantification and microscopic observation of wax accumulation as well as subcellular localization of the GL6 protein provided evidence that gl6 may be involved in the intracellular trafficking of waxes, opening a door for studying this necessary yet poorly understood process for wax loading on plant surfaces.

Assessment of orange fruit colonization by biocontrol yeasts

A scanning electron microscope study of citrus fruits was performed to assess the colonization process of antagonistic yeasts to green mould of Tarocco oranges under artificial inoculation. Yeast suspensions of Debaryomyces hansenii DBVPG 4025, Pichia guilliermondii NRRL Y 18134, P. anomala J121 and Saccharomyces cerevisiae P1.6 with or without addition of 1% CaCl₂ + 0.1% Tween 80 were evaluated. Penicillium digitatum was sprayed one hour later. Observation of fruit surface waxes revealed marked morphological diversity. Yeast cells and conidia were mostly localized on epicuticular waxes, particularly in naturally occurring small pits. The size of the wound affected the number of yeasts and conidia penetrating inside. Treatment with CaCl₂ did not affect the waxes and/or the behaviour of the yeasts and pathogen.

Long-chain alkanes and fatty acids from Ludwigia octovalvis weed leaf surface waxes as short-range attractant and ovipositional stimulant to Altica cyanea (Weber) (Coleoptera: Chrysomelidae)

The importance of leaf surface wax compounds from the rice-field weed Ludwigia octovalvis (Jacq.) Raven (Onagraceae) was determined in the flea beetle Altica cyanea (Weber) (Coleoptera: Chrysomelidae). Extraction, thin layer chromatography and GC-MS and GC-FID analyses of surface waxes of young, mature and senescent leaves revealed 20, 19 and 19 n-alkanes between n-C15 and n-C35, respectively; whereas 14, 14 and 12 free fatty acids between C12:0 and C22:0 fatty acids were identified in young, mature and senescent leaves, respectively. Tricosane was predominant n-alkane in young and mature leaves, whilst eicosane predominated in senescent leaves. Heneicosanoic acid, palmitic acid and docosanoic acid were the most abundant free fatty acids in young, mature and senescent leaves, respectively. A. cyanea females showed attraction to 0.25 mature leaf equivalent surface waxes compared with young or senescent leaves in a short glass Y-tube olfactometer bioassay. The insects were attracted to a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml−1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively, comparable with the proportions as present in 0.25 mature leaf equivalent surface waxes. A. cyanea also laid eggs on a filter paper moistened with 0.25 mature leaf equivalent surface waxes or a synthetic blend of 0.90, 1.86, 1.83, 1.95, 0.50 and 0.18 µg ml−1 petroleum ether of hexadecane, octadecane, eicosane, tricosane, palmitic acid and alpha-linolenic acid, respectively. This finding could provide a basis for monitoring of the potential biocontrol agent in the field.