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The self-sustained interactions between a flexible film and periodic vortices epitomize the spirit of fish swimming and flag flapping in nature, involving intricate patterns of flow–structure coupling. Here, we comprehensively investigate the multiple coupling states of a film in the cylinder wake mainly with experiments, complemented by theoretical solutions and nonlinear dynamical analyses. Four regimes of film motion states are identified in the parameter space spanned by the reduced velocity and the length ratio. These regimes are (i) keeping stationary, (ii) deflection flutter, (iii) hybrid flutter and (iv) periodic large-amplitude flapping, each governed by a distinct coupling mechanism, involving regular and irregular Kármán vortices, local instability of the elongated shear layers and 2P mode vortex shedding. The film futtering in regimes (ii) and (iii) is substantiated to be chaotic and bears a resemblance to the ‘entraining state’ of fish behind an obstacle in the river. The periodic flapping in regime (iv) manifests itself in an amalgam of standing and travelling waves, and has intrinsic relations to the ‘Kármán gaiting’ of fish in periodic vortices. With the spatiotemporal reconstruction for the periodic flapping, we procure the energy distributions on the film, revealing the energy transfer processes between the film and the large-scale vortices. The findings unequivocally indicate that the flow–structure interaction during the energy-release stage of the film is more intense than that during the energy-extraction stage. Given the similarities, the mathematical and physical methods presented in this work are also applicable to the research on biological undulatory locomotion.

We provide a one-stop online platform, namely, dsRNAEngineer, to help users optimize dsRNA for RNAi-based pest control.dsRNAEngineer incorporates a range of pest and non-pest species to enable large-scale transcriptome-level analysis for dsRNA design.dsRNAEngineer contains four functionalities, namely, screen-target, on-target, off-target, and multiple-target functions, to design rational dsRNAs that sufficiently target pests but are safe for non-target organisms. Over the past two decades, many double-stranded (ds)-RNAs have been synthesized to silence target genes for exploration of gene functions in pests. Some of these dsRNAs are lethal to pests, leading to a new category of pesticides. The generation of these environmentally friendly pesticides requires precise in silico design of dsRNA molecules that target pests but not non-pest organisms. Current efforts in dsRNA design focus mainly on the analysis of the target gene sequence, lacking comprehensive analysis of all transcripts of the whole transcriptome per given species, causing low efficiency and imprecise dsRNA target exploration. To address these limitations, we created the dsRNAEngineer online platform (https://dsrna-engineer.cn), which allows comprehensive and rational dsRNA design, incorporating hundreds of pest and non-pest transcriptomes. Developed functionalities include screen-target (screen conserved genes for cotargets of various pest species), on-target, off-target, and multi-target to generate optimal dsRNA for precise pest control. [Display omitted] dsRNAEngineer incorporates hundreds of pest and non-pest transcriptomes to provide comprehensive dsRNA design for pest control. With the application of several RNA-based pesticides in the field, dsRNAEngineer illustrates a framework for designing pest-specific and biosafe dsRNA, which will greatly promote the development of RNAi biotechnology as a pest control strategy. Over the past two decades, RNAi biotechnology has been intensively investigated for pest control, and several products have been registered and applied in the field. However, current methods of double-stranded (ds)RNA design lack a comprehensive analysis of all transcripts at the transcriptome level for both pest and non-pest species. To solve these problems, our timely developed tool, dsRNAEngineer (https://dsrna-engineer.cn), which has four functionalities (screen-target, on-target, off-target, and multi-target functions) was developed to help users design rational dsRNAs that sufficiently target pests but are otherwise safe for non-target organisms, based on large-scale transcriptome-level analysis of both pest and non-pest species. With the emergence of RNA pesticides, we believe that dsRNAEngineer can be considered as a gold standard in dsRNA design to promote pest control based on RNAi biotechnology.

Time-resolved particle image velocimetry and hydrogen bubble visualization are used to investigate the wake-induced transition of a 30P30N multi-element airfoil at a fixed angle of attack of 4° within the stowed chord Reynolds-number range of 1.38 × 104 to 3.05 × 104. A special transition routine, strongly affected by the slat wake, is observed in the confluent boundary layer over the 30P30N airfoil. In particular, the effects of slat-wake-triggered double-secondary vortices on the whole transition process are explored in detail. At the initial transition stage, the strong slat-wake disturbances penetrate the boundary layer of the main element and are then amplified by double-exponential growth to generate double-secondary vortices. Compared to the scenarios of simplified geometries (He et al., J. Fluid Mech., vol. 718, 2013, pp. 116–130; He & Wang, Phys. Fluids, vol. 27, 2015, 024106), the double-exponential growth provides stronger fluctuations for the transition. At the intermediate transition stage, the wake disturbances trigger the three-dimensional destabilization of these secondary vortices by direct injection or indirect induction, leading to Λ vortices. The spanwise wavelength of the consequent Λ vortices is therefore locked on by the wake disturbances. At the late transition stage, the Λ vortices evolve into hairpin vortex packets and finally contribute to an attached turbulent boundary layer above the main element. Throughout the transition process, no obvious separation occurs in the mean flow above the main element, revealing potential aerodynamic benefits.

Time-resolved particle image velocimetry (TR-PIV) is employed to investigate the vortex dynamics around the slat cove of a 30P30N multi-element airfoil at a fixed geometric angle of attack of 4 ° within the stowed chord Reynolds number range of 9.3 × 103 ≤ Rec ≤ 5.2 × 104. The results link the frequency properties to the vortex shedding patterns of the slat cusp shear layer. With increasing Rec, three types of vortex dynamics are identified: (i) no vortex shedding from the slat cusp shear layer and the absence of hydrodynamic feedback in the slat cove (9.3 × 103 ≤ Rec ≤ 1.27 × 104); (ii) impingement of shed vortices on the underside of the slat trailing edge at a steady location (1.38 × 104 ≤ Rec ≤ 1.83 × 104); (iii) impingement of shed vortices on the underside of the slat trailing edge at unsteady locations (2.41 × 104 ≤ Rec ≤ 5.2 × 104). The fluctuations generated by shed vortices link the slat cusp and trailing edge by the hydrodynamic feedback in the slat cove. Besides the fundamental frequency and its harmonics, subharmonics and fractional harmonics occur to the slat cusp shear layer in the Rec range of 2.41 × 104–5.2 × 104. Subharmonics make the impingement locations of shed vortices unsteady. Fractional harmonics trigger the secondary instability of the braid region between two consecutive vortices to generate more shed vortices. The vortex dynamics in this Rec range is found to persist to Rec ~ 106.

The oriental fruit fly (Bactrocera dorsalis) is a species of tephritid fruit fly, endemic to Southeast Asia but also introduced to many regions of the US, and it is one of the major pest species with a broad host range of cultivated and wild fruits. Although males of B. dorsalis respond strongly to methyl eugenol and this is used for monitoring and estimating populations, the molecular mechanism of the oriental fruit fly olfaction has not been elucidated yet. Therefore, in this project, using next generation sequencing technologies, we sequenced the transcriptome of the antennae of male and female adults of B. dorsalis. We identified a total of 20 candidate odorant binding proteins (OBPs), 5 candidate chemosensory proteins (CSPs), 35 candidate odorant receptors (ORs), 12 candidate ionotropic receptors (IRs) and 4 candidate sensory neuron membrane proteins (SNMPs). The sex-specific expression of these genes was determined and a subset of 9 OR genes was further characterized by qPCR with male and female antenna, head, thorax, abdomen, leg and wing samples. In the male antennae, 595 genes showed a higher expression, while 128 genes demonstrated a higher expression in the female antennae. Interestingly, 2 ORs (BdorOR13 and BdorOR14) were highly and specifically expressed in the antennae of males, and 4 ORs (BdorOR13, BdorOR16, BdorOR18 and BdorOR35) clustered with DmOR677, suggesting pheromone reception. We believe this study with these antennae-enriched OBPs, CSPs, ORs, IRs and SNMPs can play an important role in the detection of pheromones and general odorants, and so in turn our data improve our current understanding of insect olfaction at the molecular level and provide important information for disrupting the behavior of the oriental fruit fly using chemical communication methods.

Wing dimorphism is a phenomenon of phenotypic plasticity in aphid dispersal. However, the signal transduction for perceiving environmental cues (e.g., crowding) and the regulation mechanism remain elusive. Here, we found that aci-miR-9b was the only down-regulated microRNA (miRNA) in both crowding-induced wing dimorphism and during wing development in the brown citrus aphid Aphis citricidus. We determined a targeted regulatory relationship between aci-miR-9b and an ABC transporter (AcABCG4). Inhibition of aci-miR-9b increased the proportion of winged offspring under normal conditions. Overexpression of aci-miR-9b resulted in decline of the proportion of winged offspring under crowding conditions. In addition, overexpression of aci-miR-9b also resulted in malformed wings during wing development. This role of aci-miR-9b mediating wing dimorphism and development was also confirmed in the pea aphid Acyrthosiphon pisum. The downstream action of aci-miR-9b-AcABCG4 was based on the interaction with the insulin and insulin-like signaling pathway. A model for aphid wing dimorphism and development was demonstrated as the following: maternal aphids experience crowding, which results in the decrease of aci-miR-9b. This is followed by the increase of ABCG4, which then activates the insulin and insulin-like signaling pathway, thereby causing a high proportion of winged offspring. Later, the same cascade, “miR-9b-ABCG4-insulin signaling,” is again involved in wing development. Taken together, our results reveal that a signal transduction cascade mediates both wing dimorphism and development in aphids via miRNA. These findings would be useful in developing potential strategies for blocking the aphid dispersal and reducing viral transmission.

Tomographic particle image velocimetry (TPIV) measurement with six high-resolution charge-coupled device (CCD) cameras is conducted to investigate flow structures over a finite circular cylinder with an aspect ratio of 2 ( $h/d=2$ ). This short wall-mounted cylinder is fully immersed in a thick turbulent boundary layer ( $\\unicode[STIX]{x1D6FF}/h=1.025$ ). Focus is placed on the three-dimensional instantaneous vortex structures and their dynamic characteristics in the wake flow fields. Based on the present results, a refined topological model of the mean wake field behind the finite circular cylinder is proposed, where the spatial locations of the typical vortex structures and their interactions are described in more detail. Among the reported typical vortex structures (i.e. the horseshoe, tip, base, trailing and arch vortex), emphasis is laid on discussion of the tip and arch vortex. The instantaneous 3D M-shape arch vortex and an alternating large-scale streamwise vortex are first found in the present experiment, and their developments are also discussed. Therefore, it is suggested that the instantaneous finite-cylinder wake is dominated by the arch vortex system and the large-scale streamwise vortices. Moreover, in the instantaneous volumetric flow fields, both the antisymmetric and the symmetric wake behaviours are observed. With proper orthogonal decomposition (POD) analysis, the dynamic characteristics of the wake field are clarified. Different from the flow around an infinite cylinder without control, the third and fourth POD modes are characterized by low-frequency symmetric shedding. The low-frequency feature shown in the second mode pair is observed and associated with the occurrence of instantaneous symmetric 3D wake behaviour triggered by the low-aspect-ratio effect and the extension of the separated shear layer. The low frequency seems be attributed to the flapping phenomenon, i.e. oscillation of the recirculation in the backward-facing step flow. It is found that the flapping motion has a modulating effect on the occurrence of the antisymmetric shedding vortex and thus the large-scale streamwise vortex.

Flow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at the Reynolds number of 20 000. Here, the plasma actuator is placed over the pressure (lower) side of the airfoil near the trailing edge, which produces a wall jet against the free stream. This reverse flow creates a quasi-steady recirculation region, reducing the velocity over the pressure side of the airfoil. On the other hand, the air over the suction (upper) side of the airfoil is drawn by the recirculation, increasing its velocity. Measured phase-averaged vorticity and velocity fields also indicate that the recirculation region created by the plasma actuator over the pressure surface modifies the near-wake dynamics. These flow modifications around the airfoil lead to an increase in the lift coefficient, which is similar to the effect of a mechanical Gurney flap. This configuration of DBD plasma actuators, which is investigated for the first time in this study, is therefore called a virtual Gurney flap. The purpose of this investigation is to understand the mechanism of lift enhancement by virtual Gurney flaps by carefully studying the global flow behaviour over the airfoil. First, the recirculation region draws the air from the suction surface around the trailing edge. The upper shear layer then interacts with the opposite-signed shear layer from the pressure surface, creating a stronger vortex shedding from the airfoil. Secondly, the recirculation region created by a DBD plasma actuator over the pressure surface displaces the positive shear layer away from the airfoil, thereby shifting the near-wake region downwards. The virtual Gurney flap also changes the dynamics of laminar separation bubbles and associated vortical structures by accelerating laminar-to-turbulent transition through the Kelvin–Helmholtz instability mechanism. In particular, the separation point and the start of transition are advanced. The reattachment point also moves upstream with plasma control, although it is slightly delayed at a large angle of attack.

Fecundity is arguably one of the most important life history traits, as it is closely tied to fitness. Most arthropods are recognized for their extreme reproductive capacity. For example, a single female of the oriental fruit fly Bactrocera dorsalis , a highly invasive species that is one of the most destructive agricultural pests worldwide, can lay more than 3000 eggs during its life span. The ovary is crucial for insect reproduction and its development requires further investigation at the molecular level. We report here that miR-309a is a regulator of ovarian development in B . dorsalis . Our bioinformatics and molecular studies have revealed that miR-309a binds the transcription factor pannier ( GATA-binding factor A / pnr ), and this activates yolk vitellogenin 2 ( Vg 2 ) and vitellogenin receptor ( VgR ) advancing ovarian development. We further show that miR-309a is under the control of juvenile hormone (JH) and independent from 20-hydroxyecdysone. Thus, we identified a JH-controlled miR-309a/ pnr axis that regulates Vg2 and VgR to control the ovarian development. This study has further enhanced our understanding of molecular mechanisms governing ovarian development and insect reproduction. It provides a background for identifying targets for controlling important Dipteran pests.

Gust response has consistently been a concern in engineering. Critical theories have been proposed in the past to predict the unsteady lift response of an airfoil experiencing vertical gusts by Atassi, and longitudinal gusts by Greenberg. However, their applicability for an airfoil with non-zero angles of attack still needs clarification. Thus, force measurements are conducted to examine these theories’ validity and quasi-steady corrections are applied to compensate potential disparities between the idealised and real flow conditions. Velocity measurements are performed to scrutinise the effect of gusts on the flow around the airfoil, and subsequently to reveal the underlying mechanism governing the airfoil's response to gust-induced perturbations. In the study, two pitching vanes are arranged upstream to generate periodic vertical and longitudinal gusts, whereas a downstream airfoil with angles of attack of 0–12° is subjected to two gust types. It is found that Greenberg's theory demonstrates superior predictive capability in pre-stall regimes, with the potential for its effectiveness to be expanded to post-stall regimes through theoretical refinements. In contrast, Atassi's theory exhibits significant deviations from experimental outcomes across the measured angles of attack. Nevertheless, a modified version of the theory aligns better with experimental results at small angles of attack, whereas substantial discrepancies persist as the angle of attack increases. In the pre-stall regime, the aerodynamic response of the airfoil to vertical gusts displays a linear correlation with the flow angle near the leading edge. In the post-stall regime, the vertical gust induces dynamic stall of the airfoil. The flow angle has an essential effect on the lift coefficient but it alone is inadequate to dictate the trend of the lift coefficient. The vorticity statistics show that negative vortex circulation strongly correlates with the lift coefficient. Thus, further correction of the theory or a new vortex model can be expected to predict the lift variation.