Anti-adhesive effects of plant wax coverage on insect attachment

Nanoscale mesh acts as anti-adhesive surface against particulate contamination in eyes of whiteflies

In many insects the surface of the eye is nanostructured by arrays of protuberances termed ommatidial gratings which provide the cuticle with anti-reflective, anti-wetting and self-cleaning properties. The hypothesised anti-contamination role of the gratings against dust and pollen results from theoretical predictions on grating geometry and experiments on synthetic replicas of ommatidia surfaces but has not yet been proven in an animal. Whiteflies are biological test beds for anti-contamination surfaces because they deliberately distribute wax particles extruded from abdominal plates over their entire bodies. The numerous particles protect the animal against water evaporation and radiation, but may severely impair vision. Using scanning electron microscopy (SEM) and CryoSEM, we here show that the cornea of whiteflies exhibits ~ 220 nm wide mesh-like structures forming hexagonal gratings with thin ~ 40 nm connecting walls. Quantitative measurements of wax particles on the eye show that the nanostructures reduce particle contamination by more than ~ 96% compared to other areas of the cuticle. Altogether, our study is the first description of a predicted optimized grating geometry for anti-contamination in an arthropod. The findings serve as evidence of the high effectiveness of nanostructured surfaces for reducing contact area and thus adhesion forces between biological surfaces and contaminating particles.

The effect of age on the attachment ability of stick insects (Phasmatodea)

Many insect species have found their way into ageing research as small and easy-to-keep model organisms. A major sign of ageing is the loss of locomotory functions due to neuronal disorders or tissue wear. Soft and pliable attachment pads on the tarsi of insects adapt to the substrate texture to maximize their real contact area and, thereby, generate attachment during locomotion. In the majority of stick insects, adhesive microstructures covering those pads support attachment. Stick insects do not molt again after reaching the imaginal stage; hence, the cuticle of their pads is subject to continuous ageing. This study aims to quantify how attachment ability changes with age in the stick insect Sungaya aeta Hennemann, 2023 and elucidate the age effects on the material and microstructure of the attachment apparatus. Attachment performance (adhesion and friction forces) on substrates with different roughnesses was compared between two different age groups, and the change of attachment performance was monitored extending over a larger time frame. Ageing effects on the morphology of the attachment pads and the autofluorescence of the cuticle were documented using light, scanning electron, and confocal laser scanning microscopy. The results show that both adhesion and friction forces decline with age. Deflation of the pads, scarring of the cuticle, and alteration of the autofluorescence, likely indicating stiffening of the cuticle, were observed to accumulate over time. This would reduce the attachment ability of the insect, as pads lose their pliant properties and cannot properly maintain sufficient contact area with the substrate.

The Greasy Pole Syndrome in Alliaria petiolata (Brassicaceae): The Pubescence and Wax Coverage on Stems Reduce Invasion by Lasius niger Ants

To reduce negative effects of floral visitation by ants, which do not serve as reliable cross-pollinators, some plants have developed a non-floral, stem-based defense mechanism called greasy pole syndrome. In the present study, we examined the effects of two surface features (trichomes and three-dimensional epicuticular wax coverage) on stems of Alliaria petiolata plants on visiting frequencies, travelled distances, and running velocities of Lasius niger ants. The experiments were performed with stem samples prepared from different (apical and basal) stem portions showing different surface morphologies (smooth control, covered by wax and trichomes + wax, respectively). The control, mechanically wiped stem samples lacking any surface features were significantly more often visited by ants, where they travelled significantly longer distances and moved with significantly higher velocities, compared to the intact stems. The apical and basal stem portions showed no significant differences in the measured parameters. Based on data obtained, we conclude about the main contribution of the wax to the greasy pole function of the A. petiolata stem via reduction of ant adhesion to the wax-bearing stem surface, whereas trichomes presumably serve as the first barrier for ants approaching usually from the ground level and protect the fragile wax coverage from an excessive deterioration.

Parasitoid attachment ability and the host surface wettability

Climbing animals such as geckos and arthropods developed astonishing adhesive mechanisms which are fundamental for their survival and represent valuable models for biomimetic purposes. A firm adhesion to the host surface, in order to successfully lay eggs is necessary for the reproduction of most parasitoid insects. In the present study, we performed a comparative investigation on the attachment ability of four parasitoid species (the egg parasitoid Anastatus bifasciatus (Eupelmidae), the aphid parasitoid Aphidius ervi (Braconidae), the fly pupal ectoparasitoid Muscidifurax raptorellus (Pteromalidae) and the pupal parasitoid of Drosophila Trichopria drosophilae (Diapriidae)) with hosts characterized by a surface having different wettability properties. The friction force measurements were performed on smooth artificial (glass) surfaces showing different contact angles of water. We found that attachment systems of parasitoid insects are tuned to match the wettability of the host surface. Sexual dimorphism in the attachment ability of some tested species has been also observed. The obtained results are probably related to different microstructure and chemical composition of the host surfaces and to different chemical composition of the parasitoid adhesive fluid. The data here presented can be interpreted as an adaptation, especially in the female, to the physicochemical properties of the host surface and contribute to shed light on the coevolutionary processes of parasitoid insects and their hosts.

Chemical compositions and cryo-adhesive probing of the epicuticular wax crystals on fruit surface of wax gourd (Benincasa hispida)

Surface wax crystals play important roles in protecting plants from pest and disease invasions, and UV irradiation. The wax crystals are less probed individually from the fruit surfaces. Herein the morphologies, chemicals and an efficient method to sample the wax blooms of white wax gourd were addressed. Various crystalloids such as rodlets, platelets, fragments, and granules were observed, which stacked as fine wax film covering on wax gourd fruit surface. The wax blooms were effectively removed by cryo-adhesive after consecutive manipulating set by a high-end device with cylinders. Wax crystals were dominated by triterpenols and triterpenol acetates over 61 % of total crystals, followed by vey-long-chain aliphatics. Accordingly, the high-end device with cryo-adhesive provides an efficient approach to selectively probe the wax crystals from those fruits covering wax blooms. The elucidation of morphologies and chemical compositions of wax crystals may help to better understand their regulations on fruit quality traits.

Comparative analysis of the ultrastructure and adhesive secretion pathways of different smooth attachment pads of the stick insect Medauroidea extradentata (Phasmatodea)

The mechanism by which insects achieve attachment and locomotion across diverse substrates has long intrigued scientists, prompting extensive research on the functional morphology of attachment pads. In stick insects, attachment and locomotion are facilitated by two distinct types of smooth cuticular attachment pads: the primary adhesion force-generating arolium and the friction force-generating euplantulae. They are both supported by an adhesive secretion delivered into the interspace between the attachment pads and the substrate. In this study, we analysed and compared internal morphology, material composition and ultrastructure, as well as the transportation pathways in both adhesive organs in the stick insect Medauroidea extradentata using scanning electron microscopy, micro-computed tomography, light microscopy, and confocal laser scanning microscopy. Our observations revealed structural differences between both attachment pads, reflecting their distinct functionality. Furthermore, our results delineate a potential pathway for adhesive secretions, originating from exocrine epidermal cells and traversing various layers before reaching the surface. Within the attachment pad, the fluid may influence the viscoelastic properties of the pad and control the attachment/detachment process. Understanding the material composition of attachment pads and the distribution process of the adhesive secretion can potentially aid in the development of more effective artificial attachment systems.

Insect attachment on waxy plant surfaces: the effect of pad contamination by different waxes

This study focuses on experimental testing of the contamination hypothesis and examines how the contamination of insect adhesive pads with three-dimensional epicuticular waxes of different plant species contributes to the reduction of insect attachment. We measured traction forces of tethered Chrysolina fastuosa male beetles having hairy adhesive pads on nine wax-bearing plant surfaces differing in both shape and dimensions of the wax structures and examined insect adhesive organs after they have contacted waxy substrates. For comparison, we performed the experiments with the same beetle individuals on a clean glass sample just before (gl1) and immediately after (gl2) the test on a plant surface. The tested insects showed a strong reduction of the maximum traction force on all waxy plant surfaces compared to the reference experiment on glass (gl1). After beetles have walked on waxy plant substrates, their adhesive pads were contaminated with wax material, however, to different extents depending on the plant species. The insects demonstrated significantly lower values of both the maximum traction force and the first peak of the traction force and needed significantly longer time to reach the maximum force value in the gl2 test than in the gl1 test. These effects were especially pronounced in cases of the plant surfaces covered with wax projections having higher aspect ratios. The data obtained clearly indicated the impact of waxy plant surfaces on the insect ability to subsequently attach to the clean smooth surface. This effect is caused by the contamination of adhesive pads and experimentally supports the contamination hypothesis.

Chemical and structural heterogeneity of olive leaves and their trichomes

Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.

Characterization of Morphologically Distinct Components in the Tarsal Secretion of Medauroidea extradentata (Phasmatodea) Using Cryo-Scanning Electron Microscopy

Attachment to the substrate is an important phenomenon that determines the survival of many organisms. Most insects utilize wet adhesion to support attachment, which is characterized by fluids that are secreted into the interface between the tarsus and the substrates. Previous research has investigated the composition and function of tarsal secretions of different insect groups, showing that the secretions are likely viscous emulsions that contribute to attachment by generating capillary and viscous adhesion, leveling surface roughness and providing self-cleaning of the adhesive systems. Details of the structural organization of these secretions are, however, largely unknown. Here, we analyzed footprints originating from the arolium and euplantulae of the stick insect Medauroidea extradentata using cryo-scanning electron microscopy (cryo-SEM) and white light interferometry (WLI). The secretion was investigated with cryo-SEM, revealing four morphologically distinguishable components. The 3D WLI measurements of the droplet shapes and volumes over time revealed distinctly different evaporation rates for different types of droplets. Our results indicate that the subfunctionalization of the tarsal secretion is facilitated by morphologically distinct components, which are likely a result of different proportions of components within the emulsion. Understanding these components and their functions may aid in gaining insights for developing adaptive and multifunctional biomimetic adhesive systems.

Sugars and cuticular waxes impact sugarcane aphid (Melanaphis sacchari) colonization on different developmental stages of sorghum

Sugarcane aphid (SCA; Melanaphis sacchari) is a devastating pest of sorghum (Sorghum bicolor) that colonizes sorghum plants at different growth stages. Leaf surface characteristics and sugars often influence aphid settling and feeding on host plants. However, how changes in cuticular waxes and sugar levels affect SCA establishment and feeding at different development stages of sorghum have not been explored. In this study, two- and six-week-old BTx623 plants, a reference line of sorghum, was used to evaluate plant-aphid interactions. Monitoring aphid feeding behavior using Electrical Penetration Graph (EPG) technique revealed that aphids spent more time in the sieve element phase of six-week-old plants compared to two-week-old plants. Significant differences were found in the time spent to reach the first sieve element and pathway phases between the two- and six-week-old plants. However, no-choice aphid bioassays displayed that SCA population numbers were higher in two-week-old plants compared to six-week-old plants. Differences in the abundance of wax and sugar contents were analyzed to determine how these plant components influenced aphid feeding and proliferation. Among the cuticular wax compounds analyzed, α-amyrin and isoarborinone increased after 10 days of aphid infestation only in six-week-old plants. Trehalose content was significantly increased by SCA feeding on two- and six-week-old plants. Furthermore, SCA feeding depressed sucrose content and increased levels of glucose and fructose in two-week-old but not in six-week-old plants. Overall, our study indicates that plant age is a determinant for SCA feeding, and subtle changes in triterpenoids and available sugars influence SCA establishment on sorghum plants.

Genome-wide-association study and transcriptome analysis reveal the genetic basis controlling the formation of leaf wax in Brassica napus

Cuticular wax protects plants from various biotic and abiotic stresses. However, the genetic network of wax biosynthesis and the environmental factors influencing leaf wax production in rapeseed (Brassica napus) remains unclear. Here, we demonstrated the role of leaf wax in the resistance to Sclerotinia infection in rapeseed. We found that leaves grown under high light intensity had higher expression of genes involved in wax biosynthesis, and produced more wax on the leaf surface, compared with those grown under low light conditions. Genome-wide association study (GWAS) identified 89 single nucleotide polymorphisms significantly associated with leaf wax coverage. A cross-analysis between GWAS and differentially expressed genes (DEGs) in the leaf epidermis of the accessions with contrasting differences in wax content revealed 17 candidate genes that control this variation in rapeseed. Selective sweep analysis combined with DEG analysis unveiled 510 candidate genes with significant selective signatures. From the candidate genes, we selected BnaA02.LOX4, a putative lipoxygenase, and BnaCnn.CER1, BnaA02.CER3, BnaC02.CER3, and BnaA01.CER4 (ECERIFERUM1-4) that were putatively responsible for wax biosynthesis, to analyse the allelic forms and haplotypes corresponding to high or low leaf wax coverage. These data enrich our knowledge about wax formation, and provide a gene pool for breeding an ideal leaf wax content in rapeseed.

Petals Reduce Attachment of Insect Pollinators: A Case Study of the Plant Dahlia pinnata and the Fly Eristalis tenax

In order to understand whether the petal surface in "cafeteria"-type flowers, which offer their nectar and pollen to insect pollinators in an open way, is adapted to a stronger attachment of insect pollinators, we selected the plant Dahlia pinnata and the hovering fly Eristalis tenax, both being generalist species according to their pollinator's spectrum and diet, respectively. We combined cryo scanning electron microscopy examination of leaves, petals, and flower stems with force measurements of fly attachment to surfaces of these plant organs. Our results clearly distinguished two groups among tested surfaces: (1) the smooth leaf and reference smooth glass ensured a rather high attachment force of the fly; (2) the flower stem and petal significantly reduced it. The attachment force reduction on flower stems and petals is caused by different structural effects. In the first case, it is a combination of ridged topography and three-dimensional wax projections, whereas the papillate petal surface is supplemented by cuticular folds. In our opinion, these "cafeteria"-type flowers have the petals, where the colour intensity is enhanced due to papillate epidermal cells covered by cuticular folds at the micro- and nanoscale, and exactly these latter structures mainly contribute to adhesion reduction in generalist insect pollinators.

Coleoptera claws and trichome interlocking

The present study tests the hypothesis that the specialized claws with a basal tooth found in some coccinellid beetles represent an adaptation to interlock with flexible unbranched trichomes of different plants. We compared the attachment ability of three Coleoptera species, Chnootriba elaterii, Harmonia axyridis (both Coleoptera: Coccinellidae), and Chrysolina herbacea (Coleoptera: Chrysomelidae) with claws of different shape. The attachment ability of insect individuals with or without claws to a plant with leaves bearing straight non-branched trichomes (Cucurbita moschata) and to a plant with smooth leaves (Prunus laurocerasus) was measured in traction force experiments. Insect attachment ability was also tested on a resin replica of C. moschata leaf, to variate trichome stiffness, and on glass as a reference surface. Centrifugal force tester experiments were performed to compare the attachment ability of the two ladybird species to glass and to the leaf of C. moschata. Natural and artificial substrates were characterized in cryo-SEM. The collected data reveal that plant trichomes can enhance insect attachment to plant surface compared with smooth glass by increasing insect friction force, but this is directly related to the trichome stiffness. To effectively grasp soft trichomes, insects evolved special claws-associated structures, such as the dentate claws observed in Coccinellidae.

Influence of surface free energy of the substrate and flooded water on the attachment performance of stick insects (Phasmatodea) with different adhesive surface microstructures

Stick and leaf insects (Phasmatodea) are exclusively herbivores. As they settle in a broad range of habitats, they need to attach to and walk on a wide variety of plant substrates, which can vary in their surface free energy (SFE). The adhesive microstructures (AMs) on the euplantulae of phasmids are assumed to be adapted to such substrate properties. Moreover, the natural substrates can often be covered with water as a result of high relative humidity or rain. Although considerable experimental research has been carried out on different aspects of stick insect attachment, the adaptations to cope with the influence of flooded water on attachment performance remain unclear. To elucidate the role of AMs in this context, we here measured attachment forces in three species of stick insects with different AMs. The results show that attachment forces of the three species studied were influenced by the SFE and the presence of water: they all showed higher pull-off (vertical) and traction (horizontal) forces on dry surfaces, compared with when the surfaces were covered with a water film. However, the extent to which the surface properties influenced attachment differed depending on the species and its AMs. All three species showed approximately the same attachment performance on dry surfaces with different surface free energy but maintained attachment underwater to different extents.

Sorghum cuticular waxes influence host plant selection by aphids

Quantification of cuticular waxes coupled with insect bioassays and feeding behavior analysis demonstrate that long-chain C₃₂ fatty alcohol impacts host plant selection by aphids. Cuticular waxes constitute the first point of contact between plants and their environment, and it also protect plants from external stresses. However, the role of waxes in Sorghum bicolor (sorghum) against sugarcane aphid (Melanaphis sacchari), a relatively new and devastating pest of sorghum in the U.S., is not fully understood. In this study, we monitored sugarcane aphid behavior on two genotypes of young sorghum plants with different wax chemistry: a wild-type plant (bloom) with lower C₃₂ alcohol cuticular wax, and a mutant plant (bloomless) with 1.6 times the amount of wax compared to wild-type plants. No-choice aphid bioassays revealed that sugarcane aphid reproduction did not vary between wild-type and the bloomless plants. Electrical Penetration Graph (EPG) monitoring indicated that the sugarcane aphids spent comparable amount of time feeding from the sieve elements of the wild-type and bloomless plants. However, aphids spent more time feeding on the xylem sap of the bloomless plants compared to the wild-type plants. Furthermore, aphid choice assays revealed that the sugarcane aphids preferred to settle on bloomless compared to wild-type plants. Overall, our results suggest that cuticular waxes on young sorghum leaves play a critical role in influencing host plant selection by sugarcane aphids.

Effect of Leaf Trichomes in Different Species of Cucurbitaceae on Attachment Ability of the Melon Ladybird Beetle Chnootriba elaterii

This study investigates the attachment ability of the oligophagous melon ladybird beetle Chnootriba elaterii to leaves of several Cucurbitaceae species. Using cryo-SEM, we described adult and larva tarsal attachment devices and leaf surface structures (glandular and non-glandular trichomes) in Citrullus lanatus, Cucumis melo, Cucumis sativus, Cucurbita moschata, Cucurbita pepo, Ecballium elaterium, Lagenaria siceraria and Luffa aegyptiaca. Using traction force experiments and centrifugal force tests, we measured the friction force exerted by females and larvae on plant leaves. We observed that Cucurbitaceae glandular trichomes do not affect insect attachment ability at both developmental stages, suggesting some adaptation of C. elaterii to its host plants, while non-glandular trichomes, when they are dense, short and flexible, heavily reduce the attachment ability of both insect stages. When trichomes are dense but stiff, only the larval force is reduced, probably because the larva has a single claw, in contrast to the adult having paired bifid dentate claws. The data on the mechanical interaction of C. elaterii at different developmental stages with different Cucurbitaceae species, combined with data on the chemical cues involved in the host plant selection, can help to unravel the complex factors driving the coevolution between an oligophagous insect and its host plant species.

Defensive functions and potential ecological conflicts of floral stickiness

Stickiness of vegetative tissues has evolved multiple times in different plant families but is rare and understudied in flowers. While stickiness in general is thought to function primarily as a defense against herbivores, it may compromise mutualistic interactions (such as those with pollinators) in reproductive tissues. Here, we test the hypothesis that stickiness on flower petals of the High-Andean plant, Bejaria resinosa (Ericaceae), functions as a defense against florivores. We address ecological consequences and discuss potential trade-offs associated with a repellant trait expressed in flowers that mediate mutualistic interactions. In surveys and manipulative experiments, we assess florivory and resulting fitness effects on plants with sticky and non-sticky flowers in different native populations of B. resinosa in Colombia. In addition, we analyze the volatile and non-volatile components in sticky and non-sticky flower morphs to understand the chemical information context within which stickiness is expressed. We demonstrate that fruit set is strongly affected by floral stickiness but also varies with population. While identifying floral stickiness as a major defensive function, our data also suggest that the context-dependency of chemical defense functionality likely arises from differential availability of primary pollinators and potential trade-offs between chemical defense with different modes of action.

Bio-inspired materials to control and minimise insect attachment

More than three quarters of all animal species on Earth are insects, successfully inhabiting most ecosystems on the planet. Due to their opulence, insects provide the backbone of many biological processes, but also inflict adverse impacts on agricultural and stored products, buildings and human health. To countermeasure insect pests, the interactions of these animals with their surroundings have to be fully understood. This review focuses on the various forms of insect attachment, natural surfaces that have evolved to counter insect adhesion, and particularly features recently developed synthetic bio-inspired solutions. These bio-inspired solutions often enhance the variety of applicable mechanisms observed in nature and open paths for improved technological solutions that are needed in a changing global society.

Tarsal attachment structures of the biting midge Forcipomyia paludis (Diptera: Ceratopogonidae), a specialized ectoparasite of Odonata imagines

The female of the biting midge Forcipomyia paludis is a dipteran ectoparasite of West Palaearctic damselflies and dragonflies, sucking haemolymph mainly from wing veins of their hosts. This tiny midge remains firmly attached to the wings even during fast flight and aerial fight maneuvers as shown in the present paper by field studies of the large dragonfly, Cordulegaster boltonii. Since individuals of F. paludis firmly attach themselves to the challenging wing surface of their host and can successfully withstand drag and vibrations during flight, we assume that this midge species has specific microstructural adaptations on its legs for attaching to the wing surface. In our morphological study, we used scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), to study the structure of F. paludis tarsi, as well as the micro morphology of the wing surfaces of their host. Additionally, for the first time, we were able to show attachment devices of the midges dried out in contact with the host’s surface. The spatulae of the plantar setae and especially the empodial setae, are capable of replicating nanoscale wax crystals of the super hydrophobic wing coverage of the dragonfly wing membrane, in order to increase an effective contact area and therefore adhesion. This ability requires extremely soft materials of the spatula, which seems to be rather unique even in comparison to the leg attachment devices of other dipterans and other insect taxa in general.

ArabidopsisKCS5 and KCS6 Play Redundant Roles in Wax Synthesis

3-ketoacyl-CoA synthases (KCSs), as components of a fatty acid elongase (FAE) complex, play key roles in determining the chain length of very-long-chain fatty acids (VLCFAs). KCS6, taking a predominate role during the elongation from C26 to C28, is well known to play an important role in wax synthesis. KCS5 is one paralog of KCS6 and its role in wax synthesis remains unknown. Wax phenotype analysis showed that in kcs5 mutants, the total amounts of wax components derived from carbon 32 (C32) and C34 were apparently decreased in leaves, and those of C26 to C32 derivatives were obviously decreased in flowers. Heterologous yeast expression analysis showed that KCS5 alone displayed specificity towards C24 to C28 acids, and its coordination with CER2 and CER26 catalyzed the elongation of acids exceeding C28, especially displaying higher activity towards C28 acids than KCS6. BiLC experiments identified that KCS5 physically interacts with CER2 and CER26. Wax phenotype analysis of different organs in kcs5 and kcs6 single or double mutants showed that KCS6 mutation causes greater effects on the wax synthesis than KCS5 mutation in the tested organs, and simultaneous repression of both protein activities caused additive effects, suggesting that during the wax biosynthesis process, KCS5 and KCS6 play redundant roles, among which KCS6 plays a major role. In addition, simultaneous mutations of two genes nearly block drought-induced wax production, indicating that the reactions catalyzed by KCS5 and KCS6 play a critical role in the wax biosynthesis in response to drought.

Anti-icing strategies of plant surfaces: the ice formation on leaves visualized by Cryo-SEM experiments

This paper presents an experimental study on surface icing on leaves in six plant species having different surface micromorphology and wettability properties. Contrary to previous studies on ice crystallization, which have been mainly performed by using infrared video thermography, we applied a Cryo-SEM approach allowing not only characterization of plant surfaces in their native conditions but also visualization of ice crystal formation on the native plant surfaces at the micro- and nanoscales. The Cryo-SEM was also used as an experimental device to freeze water vapor, thaw ice crystals, and freeze fluid water on the plant surface again. The experiments clearly demonstrate that trichome coverage (especially with several distinct layers) and 3D wax projections can be recognized as anti-icing strategies of plants. Trichomes can prevent and delay ice formation by being nucleation points for the formation of ice from vapor and protect the plant surface from overcooling, when fluid water freezes in contact with the leaf surface. The study shows for the first time two important effects that might reduce plant cell freezing rate: the presence of air pockets between wax projections that protect from direct contact between ice crystals and the plant cuticle and elimination of fluid water after thawing and preventing further re-freezing on the surface. The detailed knowledge obtained here is not only important for plant ecology, evolution, and plant protection but also for looking for potential biomimetic strategies that reduce/avoid icing of cultural plants and artificial technical surfaces.

Volatiles and hormones mediated root-knot nematode induced wheat defense response to foliar herbivore aphid

Plant root-leaf communication signals are critical for plant defense. Numerous studies show that belowground organisms can alter systemically resistance traits in aboveground parts against herbivores. However, there are limited studies on root-knot nematode-aphid interaction. Moreover, the impact of nematode's initial density and infection time on plant defense is poorly understood. Here we aim to examine the induced defense responses by root-knot nematode Meloidogyne incognita against aboveground feeding aphid Sitobion avenae in wheat. Further, we investigated the influence of the nematode infection density as well as the length of infection in these interactions. We tested the direct and indirect defense responses triggered by M. incognita against S. avenae as well as how the responses affect the preference of Harmonia axyridis. Plant volatiles and hormones were determined to explore plant defense mechanisms that mediate aboveground-belowground defense. The photosynthetic rate was tested to examine plant tolerance strategy. We found that, both low and high densities M. incognita root infection at 7 days post inoculation (dpi) reduced the feeding of the aphid S. avenae. Behavioral assay showed that H. axyridis preferred plants co-damaged by both M. incognita and S. avenae at 7 dpi. M. incognita infection induced the changes of jasmonic acid, salicylic acid and volatile content, which mediated plant response to S. avenae. Furthermore, photosynthetic rate in wheat increased at 5 dpi under 300 M. incognita or 1000 M. incognita infection. These results suggest that plant roots induced multiple defense strategies against foliar herbivores as damages increased. Our study provides evidence of a complex dynamic response of wheat aboveground defense against aphids in response to belowground nematode damage on a temporal scale.

Comparative profiles of the cuticular chemicals and transpiration barrier properties in various organs of Chinese flowering cabbage and Chinese kale

Plant cuticle as hydrophobic barrier covers almost all aerial plant organs. Herein the cuticular chemical components and the transpiration of various organs of Chinese flowering cabbage (CFC) and Chinese kale (CK) were comprehensively characterized. Numerous species- and organ-specific differences in morphological, chemical, and physiological levels were found. The various organs were relatively smooth in surface for CFC but glaucous with hollow tube- and plate-type crystals for CK. The chemical composition of cuticular waxes were very-long chain n-alkanes, ketones, secondary alcohols with a prominent carbon chain of C₂₉ in CK, primary alcohols dominated by C₂₆ , and aldehydes prominently C₃₀ in CFC. Cutin monomers accumulated with similar levels as waxes and were dominated by α,ω-dicarboxylic acids and fatty acids without added groups. The minimum water conductance differed considerably among species and various organs ranging between 8.9 × 10^-5 (CK leaf) and 3.7 × 10^-4  m s^-1 (CFC leaf petiole). These differences in transpiration properties were proposed to be largely related to the cuticular chemicals in various organs and species. The presented results provide further insights to link the transpiration barrier functions with surface characteristics and cuticular chemicals.

In vitro transmission of 16SrIV phytoplasmas to coconut plants by Haplaxius crudus in Yucatan, Mexico

The coconut palm is an important crop worldwide. In America, it is affected by lethal yellowing (LY) disease, associated with the presence of 16SrIV ribosomal group phytoplasmas. Studies in Florida using insect-proof cages indicate Haplaxius crudus as a vector of LY phytoplasmas to palm species, including coconut. Here, an in vitro transmission system was used to verify that H. crudus collected in Yucatan, Mexico, transmit 16SrIV phytoplasmas to coconut. Three transmission trials were carried out using micropropagated coconut plants. In each trial, at least one plant was positive to 16SrIV phytoplasmas. In total, there were 4 positive plants out of 34 exposed to insects, and the phytoplasma presence was detected in root, stem, and leaf tissues. The phytoplasmas identified were 16SrIV-A and 16SrIV-D, both found in both plants and insects. In each assay where a plant was positive for either 16SrIV-A or 16SrIV-D, the same phytoplasma was present in the insect or insects used in this assay. This is the first demonstration of transmission of LY phytoplasmas to coconut plants by H. crudus in Mexico and with an in vitro system.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03069-z.

Sculpting the surface: Structural patterning of plant epidermis

Plant epidermis are multifunctional surfaces that directly affect how plants interact with animals or microorganisms and influence their ability to harvest or protect from abiotic factors. To do this, plants rely on minuscule structures that confer remarkable properties to their outer layer. These microscopic features emerge from the hierarchical organization of epidermal cells with various shapes and dimensions combined with different elaborations of the cuticle, a protective film that covers plant surfaces. Understanding the properties and functions of those tridimensional elements as well as disentangling the mechanisms that control their formation and spatial distribution warrant a multidisciplinary approach. Here we show how interdisciplinary efforts of coupling modern tools of experimental biology, physics, and chemistry with advanced computational modeling and state-of-the art microscopy are yielding broad new insights into the seemingly arcane patterning processes that sculpt the outer layer of plants.

Combined Effect of Different Flower Stem Features on the Visiting Frequency of the Generalist Ant Lasius niger: An Experimental Study

Simple Summary

Flowering plants usually attract insect pollinators by offering them nectar, pollen or other energetically valuable sources. To deter ants, which are unreliable pollinators and can act as nectar thieves, plants have developed different systems either inside the flowers or associated with the stems. The latter one, called greasy pole syndrome, is based on the combined effect of several stem features hampering the access of ants to the apically located flowers. In this study, we examined the effects of different flower stem features in the round-leaved Alexanders Smyrnium rotundifolium on the visiting frequency of the generalist ant species, the black garden ant Lasius niger. We conducted the experiments with ants running on dry wooden sticks mimicking four different types of stems. To attract ants, we placed a sweet sugar syrup droplet on a stick tip. Ants visited different types of stem-mimicking sticks with significantly different frequencies. The highest number of insects were registered on untreated stick samples, whereas the lowest visiting frequency was observed on sticks bearing cuff-like structures (serving as macroscopic physical barriers) covered with a nano/microparticle film, which caused the slipperiness of the surface. Thus, by combining macroscopic obstacles and slippery surfaces, plants can protect their flowers from undesirable crawling visitors such as ants.

Abstract

In order to understand the effects of the morphology and surface texture of flower stems in Smyrnium rotundifolium on the visiting frequency of generalist ants, we conducted experiments with Lasius niger ants running on dry wooden sticks mimicking different types of stems: (1) intact (grooved) sticks; (2) sticks painted with slaked (hydrated) lime (calcium carbonate coverage) imitating plant epicuticular wax coverage; (3) intact sticks with smooth polyester plate-shaped cuffs imitating upper leaves; and (4) intact sticks bearing cuffs painted with slaked lime. Ants were attracted by the sweet sugar syrup droplets placed on a stick tip, and the number of ants visiting the drops was counted. Our data showed significant differences in the visiting frequencies between the different types of stem-mimicking samples. The number of recorded ants progressively decreased in the following order of samples: intact sticks—painted sticks—sticks with intact cuffs—sticks with painted cuffs. These results clearly demonstrated that micro/nanoscopic surface coverages and macroscopic physical barriers, especially if combined, have a negative impact on the attractiveness of stems to ants. This study provides further evidence for the hypothesis that having a diversity of plant stems in the field, generalist ants prefer substrates where their locomotion is less hindered by obstacles and/or surface slipperiness.

Epicuticular Wax Rice Mutants Show Reduced Resistance to Rice Water Weevil (Coleoptera: Curculionidae) and Fall Armyworm (Lepidoptera: Noctuidae)

Plant structural traits can act as barriers for herbivore attachment, feeding, and oviposition. In particular, epicuticular waxes (EWs) on the aerial surfaces of many land plants offer protection from biotic and abiotic stresses. In rice (Oryza sativa L.), mutations that reduce EWs have been previously reported. However, whether such mutations affect rice water weevil (Lissorhoptrus oryzophilus Kuschel) and fall armyworm (Spodoptera frugiperda Smith) performance has not been investigated yet. These pests cause significant economic problems in important rice-producing areas of the United States. The aim of our study was to characterize the EWs of EW mutants and wild-type rice plants by gas chromatography-mass spectrometry and compare the resistance of mutant and wild-type plants against rice water weevil and fall armyworm. We hypothesized that mutants with reduced EWs would have weaker resistance to pests than wild-type plants. Three mutant lines (6-1A, 7-17A, and 11-39A) and their wild-type parent (cv. 'Sabine') were used to test this hypothesis. Levels of EWs were significantly lower in mutant lines than in the wild-type, and qualitative differences in EW composition were also observed. Reduction in EWs significantly affected performance of insects in experiments conducted under greenhouse conditions. Experiments with rice water weevils were conducted in arenas in which females were given a choice of the mutants and the wild-type for oviposition. Number of first instars emerging from the three EW mutants (an indication of oviposition preference) was higher on the three EW mutants than on wild-type plants with normal wax levels. Similarly, in no-choice experiments using whole plants or detached leaves, weight gains of armyworms on leaves were higher on the mutant lines than on the wild-type. These results indicate that EW traits are involved in rice resistance to weevils and armyworms. Understanding the plant traits that contribute to resistance to rice pests will be helpful for the development of resistant varieties for reducing pest insect damage.

Natural variation in wild tomato trichomes; selecting metabolites that contribute to insect resistance using a random forest approach

BACKGROUND

Plant-produced specialised metabolites are a powerful part of a plant's first line of defence against herbivorous insects, bacteria and fungi. Wild ancestors of present-day cultivated tomato produce a plethora of acylsugars in their type-I/IV trichomes and volatiles in their type-VI trichomes that have a potential role in plant resistance against insects. However, metabolic profiles are often complex mixtures making identification of the functionally interesting metabolites challenging. Here, we aimed to identify specialised metabolites from a wide range of wild tomato genotypes that could explain resistance to vector insects whitefly (Bemisia tabaci) and Western flower thrips (Frankliniella occidentalis). We evaluated plant resistance, determined trichome density and obtained metabolite profiles of the glandular trichomes by LC-MS (acylsugars) and GC-MS (volatiles). Using a customised Random Forest learning algorithm, we determined the contribution of specific specialised metabolites to the resistance phenotypes observed.

RESULTS

The selected wild tomato accessions showed different levels of resistance to both whiteflies and thrips. Accessions resistant to one insect can be susceptible to another. Glandular trichome density is not necessarily a good predictor for plant resistance although the density of type-I/IV trichomes, related to the production of acylsugars, appears to correlate with whitefly resistance. For type VI-trichomes, however, it seems resistance is determined by the specific content of the glands. There is a strong qualitative and quantitative variation in the metabolite profiles between different accessions, even when they are from the same species. Out of 76 acylsugars found, the random forest algorithm linked two acylsugars (S3:15 and S3:21) to whitefly resistance, but none to thrips resistance. Out of 86 volatiles detected, the sesquiterpene α-humulene was linked to whitefly susceptible accessions instead. The algorithm did not link any specific metabolite to resistance against thrips, but monoterpenes α-phellandrene, α-terpinene and β-phellandrene/D-limonene were significantly associated with susceptible tomato accessions.

CONCLUSIONS

Whiteflies and thrips are distinctly targeted by certain specialised metabolites found in wild tomatoes. The machine learning approach presented helped to identify features with efficacy toward the insect species studied. These acylsugar metabolites can be targets for breeding efforts towards the selection of insect-resistant cultivars.

Quantitative trait locus mapping combined with variant and transcriptome analyses identifies a cluster of gene candidates underlying the variation in leaf wax between upland and lowland switchgrass ecotypes

Mapping combined with expression and variant analyses in switchgrass, a crop with complex genetics, identified a cluster of candidate genes for leaf wax in a fast-evolving region of chromosome 7K. Switchgrass (Panicum virgatum L.) is a promising warm-season candidate energy crop. It occurs in two ecotypes, upland and lowland, which vary in a number of phenotypic traits, including leaf glaucousness. To initiate trait mapping, two F₂ mapping populations were developed by crossing two different F₁ sibs derived from a cross between the tetraploid lowland genotype AP13 and the tetraploid upland genotype VS16, and high-density linkage maps were generated. Quantitative trait locus (QTL) analyses of visually scored leaf glaucousness and of hydrophobicity of the abaxial leaf surface measured using a drop shape analyzer identified highly significant colocalizing QTL on chromosome 7K (Chr07K). Using a multipronged approach, we identified a cluster of genes including Pavir.7KG077009, which encodes a Type III polyketide synthase-like protein, and Pavir.7KG013754 and Pavir.7KG030500, two highly similar genes that encode putative acyl-acyl carrier protein (ACP) thioesterases, as strong candidates underlying the QTL. The lack of homoeologs for any of the three genes on Chr07N, the relatively low level of identity with other switchgrass KCS proteins and thioesterases, as well as the organization of the surrounding region suggest that Pavir.7KG077009 and Pavir.7KG013754/Pavir.7KG030500 were duplicated into a fast-evolving chromosome region, which led to their neofunctionalization. Furthermore, sequence analyses showed all three genes to be absent in the two upland compared to the two lowland accessions analyzed. This study provides an example of and practical guide for trait mapping and candidate gene identification in a complex genetic system by combining QTL mapping, transcriptomics and variant analysis.

Costs and Benefits of Wax Production in the Larvae of the Ladybeetle Scymnus nubilus

Simple Summary

Scymnus nubilus Mulsant (Coleoptera: Coccinellidae) is a tiny ladybird reaching a maximum body weight of about 1.5 mg. Despite its small body size, the individuals of this species are able to thrive in aphidophagous guilds with other predator species with stronger competitive abilities and potential to exert intraguild predation (IGP). In this study, we explore to what extent that the wax layer of S. nubilus larvae produced by dorsal epidermal cells is an effective defensive mechanism. We predict that wax production by larvae is a trait selected by adaptive evolution where some benefits (eventually protection against intraguild predation) were traded with some costs. In manipulative experiments, we found that waxless S. nubilus larvae (waxes removed artificially) were more susceptible to IGP by lacewing larvae of Chrysoperla agilis (Neuroptera: Chrysopidae). We also found that adults originating from waxless larvae were lighter than the ones originating from wax larvae, demonstrating a metabolic cost resulting from a constant need of wax production. The results indicate the potential existence of a trade-off between growth and protection associated with wax production in beetles.

Abstract

BACKGROUND: Larvae of the minute aphidophagous Scymnus nubilus Mulsant (Coleoptera: Coccinellidae) are common predators in apple orchards, covered by a wax layer that might act as a defense mechanism against natural enemies. However, the costs and benefits of protection conferred by wax remain to be assessed. We tested the following hypothesis: there is a trade-off in wax producing ladybeetles between the protection conferred by wax cover and the physiological or behavioral costs associated with its production. We predict that: (1) wax production is an efficient defensive mechanism (against intraguild predation), (2) wax production is associated with detrimental physiological (growth, reproduction) or behavioral effects (behavioral compensation: increased biomass consumption). RESULTS: Tests were carried out in the laboratory with wax and waxless larvae of S. nubilus, with and without lacewing larvae of Chrysoperla agilis (Neuroptera: Chrysopidae) being used as a potential intraguild predator of the coccinellid. Waxless individuals were more susceptible to intraguild predation by lacewing larvae. Adults originating from waxless larvae were lighter than the ones originating from wax larvae, suggesting a metabolic cost resulting from a constant need of wax production. Body-weight gain and conversion efficiency were lower in waxless larvae. Biomass consumption was similar, showing that waxless larvae did not compensate for the physiological cost by eating more aphid biomass. CONCLUSION: The results indicate the potential existence of a trade-off between growth and protection associated with wax production.

Biochemical evidence of epicuticular wax compounds involved in cotton-whitefly interaction

Sucking insects require a surface of plants on which the legs and the eggs of insects will adhere and to which insect mouthparts will access. The primary plant protection against insects is their surface property, which hinders the attachment of the insect’s legs and eggs. The epicuticular waxes chemistry influences the fine structure of the cuticular surface. In current study, an attempt was made to investigate the variation of chemical compounds in epicuticular waxes of four cotton species that classify them resistant or susceptible i.e., Gossypium abroreum, G. hirsutum, G. arboreum wax deficient mutant (GaWM3) and G. harknessi which were evaluated for their interaction with whitefly and CLCuV transmission. Gossypium hirsutum an insect and CLCuV susceptible cotton variety, was found to have four compounds namely Trichloroacetic acid, hexadecylester, P-xylenolpthalein, 2-cyclopentene-1-ol, 1-phenyl-and Phenol, 2,5-bis [1,1- dimethyl] which could interact with chitin of whitefly while only two compounds in Gossypium arboreum an insect and CLCuV resistant cotton variety could interact with chitin of whitefly. Similarly, GaWM3 and Gossypium harkasnessi were found to have only a single compound. Number of whiteflies found on leaves of G. hirsutum was much higher as compared to other cotton species. Keeping this fact in mind a wax biosynthetic gene CER3, from Arabidopsis thaliana was transformed into G. hirsutum and the plants were evaluated for their resistance against whitefly and CLCuV transmission. In microscopic analysis transgenic plants clearly showed higher amounts of leaf waxes as compared to non-transgenics. The least whitefly population and CLCuV titer of <10,000 units was found in transgenic plants compared to non-transgenic cotton where it was ≈4.5X106 units that confirmed the role of wax in insect interaction and ultimately to CLCuV transmission. This study provides novel insight on wax related compounds involved in cotton-whitefly interaction, which potentially can help in developing more efficient control strategies for this destructive pest.

Structure, Assembly and Function of Cuticle from Mechanical Perspective with Special Focus on Perianth

This review is devoted to the structure, assembly and function of cuticle. The topics are discussed from the mechanical perspective and whenever the data are available a special attention is paid to the cuticle of perianth organs, i.e., sepals, petals or tepals. The cuticle covering these organs is special in both its structure and function and some of these peculiarities are related to the cuticle mechanics. In particular, strengthening of the perianth surface is often provided by a folded cuticle that functionally resembles profiled plates, while on the surface of the petal epidermis of some plants, the cuticle is the only integral continuous layer. The perianth cuticle is distinguished also by those aspects of its mechanics and development that need further studies. In particular, more investigations are needed to explain the formation and maintenance of cuticle folding, which is typical for the perianth epidermis, and also to elucidate the mechanical properties and behavior of the perianth cuticle in situ. Gaps in our knowledge are partly due to technical problems caused by very small thicknesses of the perianth cuticle but modern tools may help to overcome these obstacles.

Phenotypic characterization of the glossy1 mutant and fine mapping of GLOSSY1 in common wheat (Triticum aestivum L.)

A novel wax locus GLOSSY1 was finely mapped to an approximately 308.1-kbp genomic interval on chromosome 2DS of wheat. The epicuticular wax, the outermost layer of aerial organs, gives plants their bluish-white (glaucous) appearance. Epicuticular wax is ubiquitous and provides an essential protective function against environmental stresses. In this study, we identified the glossy1 mutant on the basis of its glossy glume from an EMS population in the elite wheat (Triticum aestivum L.) cultivar Jimai22. The mutant had a dramatically different profile in total wax load and composition of individual wax constituents relative to the wild type, resulting in the increased cuticle permeability of glumes. The glossy glume phenotype was controlled by a single, semidominant locus mapping to the short arm of chromosome 2D, within a 308.1-kbp genomic interval that contained ten annotated protein-coding genes. These results pave the way for an in-depth analysis of the underlying genetic basis of wax formation patterns and enrich our understanding of mechanisms regulating wax metabolism.

Foliar water and solute absorption: an update

The absorption of water and solutes by plant leaves has been recognised since more than two centuries. Given the polar nature of water and solutes, the mechanisms of foliar uptake have been proposed to be similar for water and electrolytes, including nutrient solutions. Research efforts since the 19th century focussed on characterising the properties of cuticles and applying foliar sprays to crop plants as a tool for improving crop nutrition. This was accompanied by the development of hundreds of studies aimed at characterising the chemical and structural nature of plant cuticles from different species and the mechanisms of cuticular and, to a lower extent, stomatal penetration of water and solutes. The processes involved are complex and will be affected by multiple environmental, physico-chemical and physiological factors which are only partially clear to date. During the last decades, the body of evidence that water transport across leaf surfaces of native species may contribute to water balances (absorption and loss) at an ecosystem level has grown. Given the potential importance of foliar water absorption for many plant species and ecosystems as shown in recent studies, the aim of this review is to first integrate current knowledge on plant surface composition, structure, wettability and physico-chemical interactions with surface-deposited matter. The different mechanisms of foliar absorption of water and electrolytes and experimental procedures for tracing the uptake process are discussed before posing several outstanding questions which should be tackled in future studies.

Slippery flowers as a mechanism of defence against nectar-thieving ants

BACKGROUND AND AIMS

The great diversity of floral characteristics among animal-pollinated plants is commonly understood to be the result of coevolutionary interactions between plants and pollinators. Floral antagonists, such as nectar thieves, also have the potential to exert an influence upon the selection of floral characteristics, but adaptation against floral antagonists has attracted comparatively little attention. We found that the corollas of hornet-pollinated Codonopsis lanceolata (Campanulaceae) and the tepals of bee-pollinated Fritillaria koidzumiana (Liliaceae) are slippery to nectar-thieving ants living in the plant's habitat; because the flowers of both species have exposed nectaries, slippery perianths may function as a defence against nectar-thieving ants.

METHODS

We conducted a behavioural experiment and observed perianth surface microstructure by scanning electron microscopy to investigate the mechanism of slipperiness. Field experiments were conducted to test whether slippery perianths prevent floral entry by ants, and whether ant presence inside flowers affects pollination.

KEY RESULTS

Scanning electron microscopy observations indicated that the slippery surfaces were coated with epicuticular wax crystals. The perianths lost their slipperiness when wiped with hexane. Artificial bridging of the slippery surfaces using non-slippery materials allowed ants to enter flowers more frequently. Experimental introduction of live ants to the Codonopsis flowers evicted hornet pollinators and shortened the duration of pollinator visits. However, no statistical differences were found in the fruit or seed sets of flowers with and without ants.

CONCLUSIONS

Slippery perianths, most probably based on epicuticular wax crystals, prevent floral entry by ants that negatively affect pollinator behaviour. Experimental evidence of floral defence based on slippery surfaces is rare, but such a mode of defence may be widespread amongst flowering plants.

Physical and Chemical Traits of Grape Varieties Influence Drosophila suzukii Preferences and Performance

The cuticle-covered surface forms the interface between plant parts, including fruits, and their environment. The physical and chemical properties of fruit surfaces profoundly influence plant-frugivore interactions by shaping the susceptibility and suitability of the host for the attacker. Grapevine (Vitis vinifera, Vitaceae) serves as one of the various host plants of the spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), which is invasive in several parts of the world and can cause major crop losses. The susceptibility of wine towards this pest species differs widely among varieties. The objective of our study was to identify physical and chemical traits of the berry surface that may explain the differences in susceptibility of five grape varieties to D. suzukii. Both preferences of adult D. suzukii and offspring performance on intact versus dewaxed (epicuticular wax layer mechanically removed) grape berries were investigated in dual-choice assays. Moreover, the morphology and chemical composition of cuticular waxes and cutin of the different varieties were analyzed. Bioassays revealed that the epicuticular wax layer of most tested grape varieties influenced the preference behavior of adult flies; even less susceptible varieties became more susceptible after removal of these waxes. In contrast, neither offspring performance nor berry skin firmness were affected by the epicuticular wax layer. The wax morphology and the composition of both epi- and intracuticular waxes differed pronouncedly, especially between more and less susceptible varieties, while cutin was dominated by ω-OH-9/10-epoxy-C18 acid and the amount was comparable among varieties within sampling time. Our results highlight the underestimated role of the epicuticular surface and cuticle integrity in grape susceptibility to D. suzukii.

Recent Developments in Biomimetic Antifouling Materials: A Review

The term 'biomimetic' might be applied to any material or process that in some way reproduces, mimics, or is otherwise inspired by nature. Also variously termed bionic, bioinspired, biological design, or even green design, the idea of adapting or taking inspiration from a natural solution to solve a modern engineering problem has been of scientific interest since it was first proposed in the 1960s. Since then, the concept that natural materials and nature can provide inspiration for incredible breakthroughs and developments in terms of new technologies and entirely new approaches to solving technological problems has become widely accepted. This is very much evident in the fields of materials science, surface science, and coatings. In this review, we survey recent developments (primarily those within the last decade) in biomimetic approaches to antifouling, self-cleaning, or anti-biofilm technologies. We find that this field continues to mature, and emerging novel, biomimetic technologies are present at multiple stages in the development pipeline, with some becoming commercially available. However, we also note that the rate of commercialization of these technologies appears slow compared to the significant research output within the field.

Traction force measurements on male Strepsiptera (Insecta) revealed higher forces on smooth compared with hairy substrates

The aim of this study was to find out how strongly the parasitic insect Stylopsovinae, which has tarsi equipped with tenent hairs and lacking claws, attaches to different substrates. We investigated adhesion of male S. ovinae to the abdomen of its hymenopteran host (Andrena vaga), the hairier abdomen of a Bombus sp. and two artificial smooth reference surfaces with different degrees of hydrophilicity. In our experiments, the male S. ovinae developed significantly higher forces on smooth surfaces. However, the forces were significantly lower on all the hymenopteran surfaces used in the experiment. The absence of anisotropy in the force grip in cranial/caudal direction relative to the host might indirectly indicate that S. ovinae generate forces by adhesion rather than mechanical interlocking with the host hairs. The tolerance of the attachment system of S. ovinae to the substrate chemistry might be explained by the primary contribution of van der Waals interactions and not capillary forces to adhesion in S. ovinae.

Wax biosynthesis in response to danger: its regulation upon abiotic and biotic stress

The plant cuticle is the first physical barrier between land plants and their terrestrial environment. It consists of the polyester scaffold cutin embedded and sealed with organic, solvent-extractable cuticular waxes. Cuticular wax ultrastructure and chemical composition differ with plant species, developmental stage and physiological state. Despite this complexity, cuticular wax consistently serves a critical role in restricting nonstomatal water loss. It also protects the plant against other environmental stresses, including desiccation, UV radiation, microorganisms and insects. Within the broader context of plant responses to abiotic and biotic stresses, our knowledge of the explicit roles of wax crystalline structures and chemical compounds is lacking. In this review, we summarize our current knowledge of wax biosynthesis and regulation in relation to abiotic and biotic stresses and stress responses.

Role of Fruit Epicuticular Waxes in Preventing Bactrocera oleae (Diptera: Tephritidae) Attachment in Different Cultivars of Olea europaea

The olive fruit fly Bactrocera oleae (Diptera: Tephritidae) is the major pest of cultivated olives (Olea europaea L.), and a serious threat in all of the Mediterranean Region. In the present investigation, we demonstrated with traction force experiments that B. oleae female adhesion is reduced by epicuticular waxes (EWs) fruit surface, and that the olive fruit fly shows a different ability to attach to the ripe olive surface of different cultivars of O. europaea (Arbequina, Carolea, Dolce Agogia, Frantoio, Kalamata, Leccino, Manzanilla, Picholine, Nostrale di Rigali, Pendolino and San Felice) in terms of friction force and adhesion, in relation with different mean values of olive surface wettability. Cryo-scanning morphological investigation revealed that the EW present on the olive surface of the different analyzed cultivars are represented by irregular platelets varying in the orientation, thus contributing to affect the surface microroughness and wettability in the different cultivars, and consequently the olive fruit fly attachment. Further investigations to elucidate the role of EW in olive varietal resistance to the olive fruit fly in relation to the olive developmental stage and environmental conditions could be relevant to develop control methods alternative to the use of harmful pesticides.

Porous substrate affects a subsequent attachment ability of the beetle Harmonia axyridis (Coleoptera, Coccinellidae)

According to literature data, porous substrates can cause a reduction of insect attachment ability. We carried out traction experiments with adult ladybird beetles Harmonia axyridis on the smooth solid glass sample and rough porous Al₂O₃ membrane to prove the primary effect of absorption of the insect pad secretion by porous media, rather than surface roughness, on the attachment force on the porous sample. With each insect individual, a set of five experiments was conducted: (1) on glass; (2) on the porous membrane; (3-5) on glass immediately after the test on the porous surface, then after 30 min and 1 h of recovery time. On the porous substrate, the forces, being similar in females and males, were greatly reduced compared to those measured on glass. A significant difference between the force values obtained in the first (before the test on the porous sample) and second (immediately after the experiment on the porous sample) tests on glass was observed. After 30 min recovery time, beetles completely regained their attachment ability. Females produced significantly lower forces than males in all experiments on glass: the differences are probably caused by the sexual dimorphism in the microstructure of their adhesive pads. The obtained results are of fundamental importance for further application in biomimetics of novel insect-repelling surfaces and in plant protection by using porous materials.

Overexpression of WAX INDUCER1/SHINE1 Gene Enhances Wax Accumulation under Osmotic Stress and Oil Synthesis in Brassica napus

WAX INDUCER1/SHINE1 (WIN1) belongs to the AP2/EREBP transcription factor family and plays an important role in wax and cutin accumulation in plants. Here we show that BnWIN1 from Brassica napus (Bn) has dual functions in wax accumulation and oil synthesis. Overexpression (OE) of BnWIN1 led to enhanced wax accumulation and promoted growth without adverse effects on oil synthesis under salt stress conditions. Lipid profiling revealed that BnWIN1-OE plants accumulated more waxes with elevated C29-alkanes, C31-alkanes, C28-alcohol, and C29-alcohol relative to wild type (WT) under salt stress. Moreover, overexpression of BnWIN1 also increased seed oil content under normal growth conditions. BnWIN1 directly bound to the promoter region of genes encoding biotin carboxyl carrier protein 1 (BCCP1), glycerol-3-phosphate acyltransferase 9 (GPAT9), lysophosphatidic acid acyltransferase 5 (LPAT5), and diacylglycerol acyltransferase 2 (DGAT2) involved in the lipid anabolic process. Overexpression of BnWIN1 resulted in upregulated expression of numerous genes involved in de novo fatty acid synthesis, wax accumulation, and oil production. The results suggest that BnWIN1 is a transcriptional activator to regulate the biosynthesis of both extracellular and intracellular lipids.

Oviposition by the vagrant eriophyoid mite Aculops allotrichus on leaves of black locust tree, Robinia pseudoacacia

Leaf-dwelling mites often prefer to feed on young leaves and also are more likely to inhabit the abaxial leaf side. The aim of our study was to examine whether leaf age may affect production and distribution of eggs on black locust leaves by females of Aculops allotrichus. The eriophyoids were tested for 2.5 days on 'trimmed' compound leaves (with only two opposite leaflets left), which were maintained in vials filled with water. For the experiments we used leaves of three categories: (1) the 'youngest', in which both halves of the adaxial side of leaflets still adhered to each other (and usually remained folded for the next few hours), (2) 'young' with already unfolded leaflets, and (3) 'mature' with fully expanded leaflets. The tested females laid significantly more eggs on developing leaves than on 'mature' ones, although they deposited the highest number of eggs on the 'young' leaves. The distribution of eggs on adaxial or abaxial leaf sides also depended on leaf age. On the 'youngest' leaves, eriophyoids placed similar numbers of eggs on both sides of a blade. However, the older the leaf, the more willingly females deposited eggs on the abaxial side. Our biochemical and morphometrical analyses of black locust leaves indicated significant changes in the contents of nutrients and phenols within leaf tissue, and in the density of trichomes and thickness of the outer epidermal cell walls, correlated with leaf age. Their possible effects on the production and distribution of eggs on leaves by A. allotrichus are discussed.

Transcriptomic and Gas Chromatography-Mass Spectrometry Metabolomic Profiling Analysis of the Epidermis Provides Insights into Cuticular Wax Regulation in Developing 'Yuluxiang' Pear Fruit

The layer of cuticular wax covering fruits plays important roles in protecting against disease, preventing non-stomatal water loss, and extending shelf life. However, the molecular basis of cuticular wax biosynthesis in pear (Pyrus) fruits remains elusive. Our study thoroughly investigates cuticular wax biosynthesis during pear fruit development from morphologic, transcriptomic, and gas chromatography-mass spectrometry metabolomic perspectives. Our results showed that cuticular wax concentrations increased during the early stage [20-80 days after full bloom (DAFB)] from 0.64 mg/cm² (50 DAFB) to 1.75 mg/cm² (80 DAFB) and then slightly decreased to 1.22 mg/cm² during the fruit ripening period (80-140 DAFB). Scanning electron microscopy imaging indicated that wax plate crystals increased and wax structures varied during the pear fruit development. The combined transcriptomic and metabolomic profiling analysis revealed 27 genes, including 12 genes encoding transcription factors and a new structural gene (Pbr028523) encoding β-amyrin synthase, participating in the biosynthesis, transport, and regulation of cuticular wax according to their expression patterns in pear fruit. The quantitative real-time polymerase chain reaction experiments of 18 differentially expressed genes were performed and confirmed the accuracy of the RNA-Seq-derived transcript expression. A model of VLCFAs and cuticular wax synthesis and transport in pear fruit is proposed, providing a mechanistic framework for understanding cuticular wax biosynthesis in pear fruit. These results and data sets provide a foundation for the molecular events related to cuticular wax in 'Yuluxiang' pear fruit and may also help guide the functional analyses of candidate genes important for improving the cuticular wax of pear fruit in the future.

MicroR408 regulates defense response upon wounding in sweet potato

MiRNAs play diverse roles in plant development and defense responses by binding to their mRNA targets based on sequence complementarity. Here, we investigated a wound-related miR408 and its target genes in sweet potato (Ipomoea batatas) by small RNA deep sequencing and transcriptome analysis. The expression patterns of miR408 and the miR408 precursor were significantly repressed by wounding and jasmonate (JA). In contrast, expression of the putative target genes IbKCS (3-ketoacyl-CoA synthase 4), IbPCL (plantacyanin), and IbGAUT (galacturonosyltransferase 7-like) of miR408 was increased following wounding, whereas only IbKCS was increased after JA treatment. Target cleavage site mapping and Agrobacterium-mediated transient assay demonstrated that IbKCS, IbPCL, and IbGAUT were the targets of miR408. The expression of miR408 target genes was repressed in transgenic sweet potatoes overexpressing miR408. These data indicated a relationship between miR408 and its target genes. Notably, miR408-overexpressing plants showed a semi-dwarf phenotype and attenuated resistance to insect feeding, while transgenic plants overexpressing IbKCS exhibited more insect resistance than plants overexpressing only the empty vector. Collectively, sweet potato reduces the abundance of miR408 upon wounding to elevate the expression of IbKCS, IbPCL, and IbGAUT. The expression of IbKCS enhances the defense system against herbivore wounding.

OsABCG9 Is an Important ABC Transporter of Cuticular Wax Deposition in Rice

The importance of the cuticular layer in regulating a plant's water status and providing protection from environmental challenges has been recognized for a long time. The cuticular layer in plants restricts non-stomatal water loss and protects plants against damage from pathogen infection and UV radiation. Much genetic and biochemical research has been done about cutin and wax transportation in Arabidopsis thaliana, but little is known about it in rice. Here, we report that a rice ATP-binding cassette (ABC) transporter, OsABCG9, is essential for normal development during vegetative growth and could play a critical role in the transportation of epicuticular wax in rice. Rice phenotypes with mutated OsABCG9 exhibited growth retardation and sensitivity to low humidity. The total amount of cuticular wax on the leaves of the osabcg9-1 mutant diminished by 53% compared with the wild type, and wax crystals disappeared completely in osabcg9-2 mutant leaves. However, OsABCG9 does not seem to be involved in cutin transportation, even though its ortholog in Arabidopsis, AtABCG11, transports both wax and cutin. Furthermore, the osabcg9-1 mutant had increased leaf chlorophyll leaching and more severe drought susceptibility. This study provides new insights about differences between rice and A. thaliana in wax and cutin transportation associated with the ABCG family during evolution.