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The degeneration in flight ability in beetles has rarely been studied in detail with regard to the polymorphism of flight traits within species. However, intraspecific diversity in flight traits means that the flight ability of species is in the process of degenerating, which could provide important insights into how flight ability in beetles degenerates. In this study, the flight muscle and hind wings of the genus Synuchus in Japan were studied, which revealed the morphological status of flight traits in 21 species of Synuchus. Several species in this genus were found to show intraspecific polymorphisms in the states of the flight muscle and hind wings, and in particular, the very high diversity of different types of hind wings. These results indicate that this genus contains a mixture of species at various stages in the degeneration of the ability to fly.

Locusts (Locusta migratoria) have outstanding flying abilities, and most of their lift is provided by their hind wings. Insect aerodynamic performance is strongly affected by wing deformation during stroke, which is closely related to its functional morphology (particularly its mechanical properties). The cross-vein is one of the main morphologies in the hind wing of locusts. However, few studies on the mechanical properties of cross-veins have been conducted. This study evaluated the cross-veins of the locust hind wing using uniaxial tensile tester, scanning electron microscope, and finite element methods. Four cross-vein types were identified at different locations on the hind wing, including periodical semi- and full-ellipsoidal humps and periodical semi- and full-conical humps. The four cross-veins showed similar tensile stiffness but differed in bending compliance. We suggest that the mechanical properties of the four cross-veins can be attributed to their physiological functions. This study elucidates cross-veins of locust hind wing and contributes our understanding of the flapping flight mechanism in locusts.

The scarab beetle is an herbivorous pest that causes considerable damage to various agricultural crops. The characteristics of the hind wings have rarely been utilized as indicators for species identification, particularly within the genus Holotrichia. To evaluate the potential of hind wing traits in species identification and gender differentiation, we extracted 25 landmarks from 125 samples of three beetle species (Holotrichia diomphalia, H. titanis, and H. oblita) using TPSDig2 v2.31, with each hind wing image analyzed three times. These landmarks were employed to analyze variations in wing size and shape among species and sexes, and a cross-validation test was conducted in MorphoJ v1.06 to assess classification accuracy. The results demonstrate that both female and male samples exhibit significant differences in wing size and shape variations across species, but not between sexes. Allometry accounts for 16.92% and 25.35% of total shape variation in females and males, separately. After correcting for allometric effects, classification accuracy improves for these beetles. From further analysis, it can be observed that female wings exhibit a wider and shorter morphology in comparison to the more slender and elongated wings of males. In terms of interspecific differences, H. oblita females displayed narrow and elongated wings, whereas H. diomphalia females had a more rectangular wing shape. Among males, the degree of wing narrowness decreased in the order of H. oblita, H. titanis, and H. diomphalia.

Deployable hind wings of beetles led to a bio-inspired idea to design deployable micro aerial vehicles (MAVs) to meet the requirement of miniaturization. In this paper, a bionic deployable wing (BD-W) model is designed based on the folding mechanism and elliptical wing vein structure of the Protaetia brevitarsis hindwing, and its structural static and aerodynamic characteristics are analyzed by using ANSYS Workbench. Finally, the 3D-printed bionic deployable wing was tested in a wind tunnel and compared with simulation experiments to explore the effects of different incoming velocity, flapping frequency, and angle of attack on its aerodynamic characteristics, which resulted in the optimal combination of the tested parameters, among which, the incoming velocity is 3 m/s, the flapping frequency is 10 Hz, the angle of attack is 15°, and the lift-to-drag ratio of this parameter combination is 4.91. The results provide a theoretical basis and technical reference for the further development of bionic flapping wing for MAV applications.

In most beetles, the hind wings are thin and fragile; when at rest, they are held over the back of the beetle. When the hind wing unfolds, it provides the necessary aerodynamic forces for flight. In this paper, we investigate the hydraulic mechanism of the unfolding process of the hind wings in Dorcus titanus platymelus (Oder: Coleoptera). The wing unfolding process of Dorcus titanus platymelus was examined using high speed camera sequences (400 frames/s), and the hydraulic pressure in the veins was measured with a biological pressure sensor and dynamic signal acquisition and analysis (DSA) during the expansion process. We found that the total time for the release of hydraulic pressure during wing folding is longer than the time required for unfolding. The pressure is proportional to the length of the wings and the body mass of the beetle. A retinal camera was used to investigate the fluid direction. We found that the peak pressures correspond to two main cross-folding joint expansions in the hind wing. These observations strongly suggest that blood pressure facilitates the extension of hind wings during unfolding.

When beetles are not in flight, their hind wings are folded and hidden under the elytra to reduce their size. This provided inspiration for the design of flapping-wing micro aerial vehicles (FWMAVs). In this paper, microstructures and nanomechanical properties of three beetle species with different wing folding ratios living in different environments were investigated. Factors affecting their flight performance, that is, wind speed, folding ratio, aspect ratio, and flapping frequency, were examined using a wind tunnel. It was found that the wing folding ratio correlated with the lift force of the beetles. Wind speed, folding ratio, aspect ratio, and flapping frequency had a combined effect on the flight performance of the beetles. The results will be helpful to design new deployable FWMAVs.

A taxonomic revision of the genus Trichohoplorana Breuning, 1961 is presented. A junior synonym of Trichohoplorana , Ipochiromima Sama & Sudre, 2009, syn. nov. , is proposed. A junior synonym of T. dureli Breuning, 1961, I. sikkimensis (Breuning, 1982), syn. nov. , is proposed. Trichohoplorana is newly recorded from Vietnam. A new species, T. nigeralba sp. nov. is described from Vietnam. Trichohoplorana luteomaculata Gouverneur, 2016 is newly recorded from China and Vietnam. Hind wings and male terminalia of T. luteomaculata are described for the first time. Trichohoplorana is redescribed, and a key to Trichohoplorana species is presented.

A method for recognizing the final stadium and the four preceding stadia of dragonfly nymphs (Odonata: Anisoptera) was derived by dividing hind wing sheath length (WSL) by maximum head width (HW). Based on measurements for 15 species representing all seven North American families, five stadia can be delineated, counting backwards from the final (F-0) to the four preceding stadia (F-1, F-2, F-3, and F-4). The ratio WSL/HW over all species ranged as follows: F-0, 0.89–1.39 (mean 1.16); F-1, 0.57–0.88 (mean 0.70); F-2, 0.36–0.61 (mean 0.46); F-3, 0.24–0.44 (mean 0.32); and F-4, 0.15–0.32 (mean 0.23). As a crude guide, a ratio near 1 or greater indicates F-0, about two-thirds indicates F-1, about one-half indicates F-2, about one-third indicates F-3, and about one-fourth indicates F-4. Plathemis lydia (Libellulidae) had the highest WSL/HW ratio in F-0 (1.32–1.39).

In this paper, a beetle with excellent flight ability and a large folding ratio of its hind wings is selected as the biomimetic design. We mimicked the geometric patterns formed during the folding process of the hind wings to construct a deployable mechanism while calculating the sector angles and dihedral angles of the origami mechanism. In the expandable structure of thick plates, hinge-like steps are added on the thick plate to effectively avoid interference motion caused by the folding of the thick plate. The kinematic characteristics of two deployable mechanisms were characterized by ADAMS 2018 software to verify the feasibility of the mechanism design. The finite element method is used to analyze the structural performance of the deployable mechanism, and its modal response is analyzed in both unfolded and folded configurations. The aerodynamic generation of a spatially deployable wing is characterized by computational fluid dynamics (CFD) to study the vortex characteristics at different frame rates. Based on the aerodynamic parameters obtained from CFD simulation, a wavelet neural network is introduced to learn and train the aerodynamic parameters.

Most beetles belonging to the subfamily Carabinae of the family Carabidae (so-called carabid ground beetles) cannot fly, because their hind-wings are highly degenerated. However, about half of the species in the subtribe Calosomina within the same subfamily can fly. From extensive morphological examinations of the hind-wings of Carabinae species in conjunction with DNA molecular phylogenetic trees, the process and possible causes of hind-wing degeneration in the Carabinae are discussed.