Wing interference patterns are consistent and sexually dimorphic in the four families of crane flies (Diptera, Tipuloidea)

Wing interference patterns (WIP) are stable structural colors in insect wings caused by thin-film interference. This study seeks to establish WIP as a stable, sexually dimorphic, species-level character across the four families of Tipuloidea and investigate generic level WIP. Thirteen species of Tipuloidea were selected from museum specimens in the Academy of Natural Sciences of Drexel University collection. One wing from a male and female of each representative species was excised and mounted to a slide with coverslip, placed against a black background, and imaged using an integrated microscope camera. Images were minimally retouched but otherwise unchanged. Descriptions of the WIP for each sex of each species are provided. Twelve of thirteen species imaged had WIP, which were stable and species specific while eight of those twelve had sexually dimorphic WIP. Comparisons of three species of Nephrotoma were inconclusive regarding a generic level WIP. Gnophomyia tristissima had higher intraspecific variation than other species examined. This study confirms stable, species specific WIP in all four families of crane flies for the first time. More research must be done regarding generic-level stability of WIP in crane flies as well as the role sexual and natural selection play in the evolution of wing interference patterns in insects.

Fully-printed metamaterial-type flexible wings with controllable flight characteristics

Insect wings are an outstanding example of how a proper interplay of rigid and flexible materials enables an intricate flapping flight accompanied by sound. The understanding of the aerodynamics and acoustics of insect wings have enabled the development of man-made flying robotic vehicles and explained basic mechanisms of sound generation by natural flyers. This work proposes the concept of artificial wings with a periodic pattern, inspired by metamaterials, and explores how the pattern geometry can be used to control the aerodynamic and acoustic characteristics of the wing. For this, we analyzed bio-inspired wings with anisotropic honeycomb patterns flapping at a low frequency and developed a multi-parameter optimization procedure to tune the pattern design in order to increase lift and, simultaneously, manipulate the produced sound. Our analysis is based on the finite-element solution to a transient three-dimensional fluid-structure interactions problem. The two-way coupling is described by incompressible Navier-Stokes equations for viscous air and structural equations of motion for a wing undergoing large deformations. We manufactured three wing samples by means of 3D printing and validated their robustness and dynamics experimentally. Importantly, we showed that the proposed wings can sustain long-term resonance excitation that opens a possibility to implement resonance-type flights inherent to certain natural flyers. Our results confirm the feasibility of the metamaterial patterns to control the flapping flight dynamics and can open new perspectives for applications of 3D-printed patterned wings, e.g., in the design of drones with the target sound.

Flight activity and age cause wing damage in house flies

Wing damage attenuates aerial performance in many flying animals such as birds, bats and insects. Especially insect wings are fragile and light in order to reduce inertial power requirements for flight at elevated wing flapping frequencies. There is a continuing debate on the factors causing wing damage in insects including collisions with objects, mechanical stress during flight activity, and aging. This experimental study is engaged with the reasons and significance of wing damage for flight in the house fly Musca domestica. We determined natural wing area loss under two housing conditions and recorded flight activity and flight ability throughout the animals’ lifetime. Our data show that wing damage occurs on average after 6 h of flight, is sex-specific, and depends on housing conditions. Statistical tests show that both physiological age and flight activity have similar significance as predictors for wing damage. Tests on freely flying flies showed that minimum wing area for active flight is approximately 10-34% below the initial area and requires a left-right wing area asymmetry of less than approximately 25%. Our findings broadly confirm predictions from simple aerodynamic theory based on mean wing velocity and area, and are also consistent with previous wing damage measurements in other insect species.

Insect wing 3D printing

Insects have acquired various types of wings over their course of evolution and have become the most successful terrestrial animals. Consequently, the essence of their excellent environmental adaptability and locomotive ability should be clarified; a simple and versatile method to artificially reproduce the complex structure and various functions of these innumerable types of wings is necessary. This study presents a simple integral forming method for an insect-wing-type composite structure by 3D printing wing frames directly onto thin films. The artificial venation generation algorithm based on the centroidal Voronoi diagram, which can be observed in the wings of dragonflies, was used to design the complex mechanical properties of artificial wings. Furthermore, we implemented two representative functions found in actual insect wings: folding and coupling. The proposed crease pattern design software developed based on a beetle hindwing enables the 3D printing of foldable wings of any shape. In coupling-type wings, the forewing and hindwing are connected to form a single large wing during flight; these wings can be stored compactly by disconnecting and stacking them like cicada wings.

Flight efficiency is a key to diverse wing morphologies in small insects

Insect wings are hybrid structures that are typically composed of veins and solid membranes. In some of the smallest flying insects, however, the wing membrane is replaced by hair-like bristles attached to a solid root. Bristles and membranous wing surfaces coexist in small but not in large insect species. There is no satisfying explanation for this finding as aerodynamic force production is always smaller in bristled than solid wings. This computational study suggests that the diversity of wing structure in small insects results from aerodynamic efficiency rather than from the requirements to produce elevated forces for flight. The tested wings vary from fully membranous to sparsely bristled and were flapped around a wing root with lift- and drag-based wing kinematic patterns and at different Reynolds numbers ( Re ). The results show that the decrease in aerodynamic efficiency with decreasing surface solidity is significantly smaller at Re = 4 than Re = 57. A replacement of wing membrane by bristles thus causes less change in energetic costs for flight in small compared to large insects. As a consequence, small insects may fly with bristled and solid wing surfaces at similar efficacy, while larger insects must use membranous wings for an efficient production of flight forces. The above findings are significant for the biological fitness and dispersal of insects that fly at elevated energy expenditures.

The Daphnia carapace and the origin of novel structures

SummaryUnderstanding how novel structures arise is a central question in evolution. The carapace of the waterflea Daphnia is a bivalved “cape” of exoskeleton that has been proposed to be one of many novel arthropod structures that arose through repeated co-option of genes that also pattern insect wings1–3. To determine whether the Daphnia carapace is a novel structure, we compare the expression of pannier, araucan, and vestigial between Daphnia, Parhyale, and Tribolium. Our results suggest that the Daphnia carapace did not arise by co-option, but instead derives from an ancestral exite (lateral lobe) that emerges from a proximal leg segment that was incorporated into the Daphnia body wall. The Daphnia carapace therefore appears to be homologous to the Parhyale tergal plate and the insect wing4. Remarkably, the vestigial-positive region that gives rise to the Daphnia carapace appears to be present in Parhyale5 and Tribolium as a small, inconspicuous protrusion. Similarly, the vestigial-positive developmental fields that form tergal plates in Parhyale appear to be present in Daphnia, even though Daphnia does not form tergal plates. Thus, rather than a novel structure resulting from gene co-option, the Daphnia carapace appears to have arisen from a shared, ancestral developmental field that persists in a cryptic state in other arthropod lineages. Cryptic persistence of unrecognized serially homologous developmental fields may thus be a general solution for the origin of novel structures. Our simple molecular triangulation strategy, which does not require functional studies, can illuminate the homologies of long-debated structures on the legs and body wall of arthropods.

Insect Wing Buckling Influences Stress and Stability During Collisions

Flapping insect wings frequently collide with vegetation and other obstacles during flight. Repeated collisions may irreversibly damage the insect wing, thereby compromising the insect’s ability to fly. Further, reaction torques caused by the collision may destabilize the insect and hinder its ability to maneuver. To mitigate the adverse effects of impact, some insect wings are equipped with a flexible joint called a “costal break.” The costal break buckles once it exceeds a critical angle, which is believed to improve flight stability and prevent irreversible wing damage. However, to our knowledge, there are no models to predict the dynamics of the costal break. Through this research, we develop a simple model of an insect wing with a costal break. The wing was modeled as two beams interconnected by a torsional spring, where the stiffness of the torsional spring instantaneously decreases once it has exceeded a critical angle. We conducted a series of static tests to approximate model parameters. Then, we used numerical simulation to estimate the peak stresses and reaction moments experienced by the wing during a collision. We found that costal break increased the wing’s natural frequency by about 50% compared to a homogeneous wing and thus reduced the stress associated with normal flapping. Buckling did not significantly affect peak stresses during collision. Joint buckling reduced the peak reaction moment by about 32%, suggesting that the costal break enhances flight stability.