Codling moths,
Cydia pomonella
L. (Lepidoptera, Tortricidae), of the first generation deposit eggs on apple leaves in the vicinity of small fruits. The choice of the suitable oviposition sites and ...proper fixation of eggs are expected to be crucial factors for the survival of the offspring. In this study, we investigated egg adhesion of the codling moth to leaf surfaces of different cultivars of the domestic apple,
Malus domestica
Borkh., by measuring the pull-off force required to detach the eggs from leaves. Since surface features may influence insect egg adhesion, morphological and physicochemical properties (wettability, free surface energy) of these leaf surfaces were analyzed. Furthermore, eggs and their adhesives covering leaf surfaces were visualized. Eggs on the smooth upper leaf surfaces of all tested cultivars required significantly similar pull-off forces to be detached, at a total average of 6.0 mN. Up to 2–3 times stronger pull-off forces had to be applied to detach eggs from trichome-covered lower leaves, and these forces differed significantly between cultivars. The role of leaf surface properties is discussed in the context of egg adhesion, oviposition site choice, female attachment, as well as neonate locomotion speed and survival. The obtained results shed light on the susceptibility of various apple cultivars and leaf surfaces to the infestation of apple trees by first-generation codling moths.
In the late growing season of apples, most eggs of the codling moth, Cydia pomonella L. (Lepidoptera, Tortricidae), of the second and third generations are deposited directly on fruits. The apple ...fruit surface is densely covered by three-dimensional micro- and nanoprojections, the epicuticular wax crystals, emerging from an underlying wax film. These epicuticular waxes render the apple fruit surface hydrophobic, which could affect the attachment of insect legs and eggs to it. A better survival of the codling moth offspring is expected to be ensured by the selection of suitable oviposition sites by females, as well as by a proper adhesion of deposited eggs to these sites. In this study, we investigated egg adhesion of the codling moth to the fruit surface of different cultivars of the domestic apple, Malus domestica Borkh., by measuring the pull-off force required to detach eggs from fruits. Since surface characteristics may influence insect egg adhesion, the information about morphological and physicochemical properties of the fruit surface is crucial for understanding oviposition site selection by females. In the present study, surface morphology, wettability, and free surface energy of the apple cultivars ‘Boskoop’, ‘Elstar’, ‘Golden Delicious’, ‘Jonica’, and ‘Topaz’ were analyzed. Eggs adhered tightly to the fruit surface of all apple cultivars tested: pull-off forces averaged 63.9 mN. These forces are four- to tenfold stronger than those previously measured on adaxial and abaxial leaf surfaces of the identical apple cultivars. The mechanisms used by the moth to fix its eggs on the waxy surface of apple fruits, and the influence of fruit surface properties on egg glue adhesion are discussed. Furthermore, the results are debated in the context of the oviposition site selection by females, and its role in offspring survival of the second and third generations of the codling moth.
Although snake-like robots are only rarely used in real applications, numerous designs have been proposed by different researchers. In addition to the capability of grasping objects by bending their ...body around them, snakes travel in various environments by using different gaits. To move forward, they need a skin which provides friction anisotropy to the ground. The designs of snake-like robots vary in their actuation mechanism as well as in the design of their artificial skin. In this work, we present a novel design of an artificial snakeskin. The design is related to an application in soft robotics, but is not restricted to this type of robot. Since soft robots are flexible and can stretch, our artificial skin is also able to. It is inspired by the belly of snakes and provides friction anisotropy in forward-reverse direction. To achieve this, we embed scales with a specific angle of attack into a flexible base body. In the experimental investigation of the artificial snakeskin, we determine the friction anisotropy for two base body materials with different stiffness and for three angles of attack. Although the development of the artificial skin is at an early stage, the results of the experimental investigation are promising. The dynamic behavior of the artificial snakeskin indicates that a flexible base material reduces friction in forward direction and increases friction in reverse direction, thus enhancing friction anisotropy. Furthermore, the results obtained give important information for further design improvements in future.
Presentation of a modular and stretchable artificial snakeskin Systematic investigation of the frictional properties when changing the angle of attack of the scales and the softness of the base material the scales are embedded in A soft base material increases friction anisotropy and reduces inaccuracies of hand manufacturing Demonstration of a soft robotic actuator which uses the artificial snakeskin for crawling.
•Presentation of a modular and stretchable artificial snakeskin.•Systematic investigation of the frictional properties when changing the angle of attack of the scales and the softness of the base material in which the scales are embedded.•A soft base material increases friction anisotropy and reduces inaccuracies of hand manufacturing.•Demonstration of a soft robotic actuator which uses the artificial snakeskin for crawling.
Recent progress in space research and in particular appearance of complex movable constructions with a number of components exposed to the extreme conditions of open space causes a strong demand for ...development of new tribological and adhesion systems which are able to resist such conditions. In the last few years, many engineering solutions in the field of tribology and adhesion have been found based on “biomimetics approach” that is searching for ideas originally created by living nature and optimized during billions of years of natural selection. Surprisingly some of the living creatures are found to be optimized even for survival for a long time in the conditions of open space. Such ability is very promising from the point of view of development of new adhesives for future space applications. In this paper we discuss what we can learn in this context from the so-called “water bears” (tardigrades) in a combination with some other features, already adopted to reversible technical adhesives from other animals, such as insects and Gecko lizards.
Leafhoppers (Insecta, Hemiptera, Cicadellidae) actively coat their integuments with brochosomes, hollow proteinaceous spheres of usually 200-700 nm in diameter, with honeycombed walls. The coats have ...been previously suggested to act as a water-repellent and anti-adhesive protective barrier against the insect's own exudates. We estimated their wettability through contact angle (CA) measurements of water, diiodomethane, ethylene glycol and ethanol on detached wings of the leafhoppers Alnetoidia alneti, Athysanus argentarius and Cicadella viridis. Intact brochosome-coated integuments were repellent to all test liquids, except ethanol, and exhibited superhydrophobicity, with the average water CAs of 165-172°, and the apparent surface free energy (SFE) estimates not exceeding 0.74 mN m⁻¹. By contrast, the integuments from which brochosomes were removed with a peeling technique using fluid polyvinylsiloxane displayed water CAs of only 103-129° and SFEs above 20 mN m⁻¹. Observations of water-sprayed wings in a cryo-scanning electron microscope confirmed that brochosomal coats prevented water from contacting the integument. Their superhydrophobic properties appear to result from fractal roughness, which dramatically reduces the area of contact with high-surface-tension liquids, including, presumably, leafhopper exudates.
•The BG method is used to identify elastic and adhesive properties of materials.•The method has been extended to a two-stage process of fitting experimental data.•A new objective functional of the ...method has been introduced.•The accuracy of the method has been verified using two independent experiments.
The depth-sensing indentation (DSI) is currently one of the main experimental techniques for studying elastic properties of materials of small volumes. Usually DSI tests are performed using sharp pyramidal indenters and the load-displacement curves obtained are used for estimations of elastic moduli of materials, while the curve analysis for these estimations is based on the assumptions of the Hertz contact theory of non-adhesive contact. The Borodich–Galanov (BG) method provides an alternative methodology for estimations of the elastic moduli along with estimations of the work of adhesion of the contacting pair in a single experiment using the experimental DSI data for spherical indenters. The method assumes fitting the experimental points of the load-displacement curves using a dimensionless expression of an appropriate theory of adhesive contact. Earlier numerical simulations showed that the BG method was robust. Here first the original BG method is modified and then its accuracy in the estimation of the reduced elastic modulus is directly tested by comparison with the results of conventional tensile tests.
The method modification is twofold: (i) a two-stage fitting of the theoretical DSI dependency to the experimental data is used and (ii) a new objective functional is introduced which minimizes the squared norm of difference between the theoretical curve and the one used in preliminary data fitting. The direct experimental validation of accuracy and robustness of the BG method has two independent steps. First the material properties of polyvinyl siloxane (PVS) are determined from a DSI data by means of the modified BG method; and then the obtained results for the reduced elastic modulus are compared with the results of tensile tests on dumbbell specimens made of the same charge of PVS.
Comparison of the results of the two experiments showed that the absolute minimum in relative difference between individual identified values of the reduced elastic modulus in the two experiments was 3.80%; the absolute maximum of the same quantity was 27.38%; the relative difference in averaged values of the reduced elastic modulus varied in the range 16.20 ... 17.09% depending on particular settings used during preliminary fitting. Hence, the comparison of the results shows that the experimental values of the elastic modulus obtained by the tensile tests are in good agreement with the results of the extended BG method. Our analysis shows that unaccounted factors and phenomena tend to decrease the difference in the results of the two experiments. Thus, the robustness and accuracy of the proposed extension of the BG method has been directly validated.
During their lifespan, the long and narrow tibiae of the stick insect Carausius morosus (Sinéty, 1901) experience substantial compressive loads. The mechanical load on the tibiae increases as the ...weight of the insect rises. The increase in the body weight is accompanied by a notable increase in the insect's body size and, accordingly, by an increase in the length of the tibiae. These changes can both raise the risk of buckling of the tibiae. In this study, we track changes in the material and geometric properties of the hindleg tibia of C. morosus during growth. The results show that although buckling (either by Euler buckling or local buckling) is the dominant failure mode under compression, the tibia is well capable of maintaining its buckling resistance in each postembryonic developmental stage. This is found to be essentially the result of a compromise between the increasing slenderness of the tibia and its increasing material stiffness. The use of an optimal radius to thickness ratio, a soft resilin-dominated core, and chitin fibres oriented in both longitudinal and circumferential directions are presumably additional strategies preventing buckling of the tibia. This study, providing the first quantitative data on changes in the biomechanical properties of cuticle during the entire life of an insect, is expected to shed more light on the structure-property-function relationship in this complex biological composite.
The larvae of some sawfly species belonging to the family Tenthredinidae (Hymenoptera) are capable of ‘easy bleeding’, an anti-predator defence strategy based on a specialised cuticle that can ...readily break, which frees droplets of distasteful haemolymph. Using high-resolution cryo-scanning electron microscopy, we compared the cuticle surface between easy bleeder (Rhadinoceraea micans, Phymatocera aterrima, Aneugmenus padi) and non-easy bleeder (Strongylogaster multifasciata, Nematus pavidus, Arge pagana) sawfly species. We detected crystalline waxes only on the cuticle surface of easy bleeders. Wax crystals varied in shape and dimension depending on species. We assume the reduction of surface wettability by oozed haemolymph to be the primary function of the wax crystal coverage in the easy bleeding defence strategy.
► Easy bleeding is an anti-predator defence strategy of larvae in some sawfly species.► The integument of easy bleeders, adapted to disrupt easily, shows surface sculptures.► Moreover, crystalline waxes of specific shape and dimension cover the integument.► Sculptures and waxes render the integument hydrophobic, which is used in defence.
While the morphology of the adhesive system of geckos has been investigated predominantly in a single species, the tokay Gekko gecko (Linnaeus, 1758), compared to that, there is still the need to ...examine those traits in a broad diversity of gecko species. Here we focus on the Asian representatives of eublepharid geckos, as a closely related group within Gekkota, and study the anatomy of micro-ornamentation as well as the morphology of bone structures of toes and tails in three species of Eublepharidae. Surface microstructures are described by using SEM microscopy. Osseous structures present in limbs and in the tail are compared by using 3D analysis based on micro-CT data. The presence of epidermal outgrowths associated with friction-enhancement in arboreal representatives of Eublepharidae and the lack of setae in ground-dwelling species is discussed. A clear allocation of the term ‘seta’ is provided. Apart from a comparative consideration of ecomorphological specialisations in limbs, adaptations to the lateral flexibility of the prehensile tail found in Aeluroscalabotes felinus (Günther, 1864) are illustrated.
Correlations between the life style of the species studied and the morphology of their osseous structures in limbs and tail are shown and their significance for locomotion is outlined.
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