Structure and evolution of the stigmapophysis-A unique repose wing-coupling structure in Psocodea

A cuticular protein, BgCPLCP1, contributes to insecticide resistance by thickening the cockroach endocuticle

Overuse of insecticides has led to severe environmental problems. Insect cuticle, which consists mainly of chitin, proteins and a thin outer lipid layer, serves multiple functions. Its prominent role is as a physical barrier that impedes the penetration of xenobiotics, including insecticides. Blattella germanica (L.) is a major worldwide indoor pest that causes allergic disease and asthma. Extensive use of pyrethroid insecticides, including β-cypermethrin, has selected for the rapid and independent evolution of resistance in cockroach populations on a global scale. We demonstrated that BgCPLCP1, the first CPLCP (cuticular proteins of low complexity with a highly repetitive proline-rich region) family cuticular protein in order Blattodea, contributes to insecticide penetration resistance. Silencing BgCPLCP1 resulted in 85.0 %-85.7 % and 81.0 %-82.0 % thinner cuticle (and especially thinner endocuticle) in the insecticide-susceptible (S) and β-cypermethrin-resistant (R) strains, respectively. The thinner and more permeable cuticles resulted in 14.4 % and 20.0 % lower survival of β-cypermethrin-treated S- and R-strain cockroaches, respectively. This study advances our understanding of cuticular penetration resistance in insects and opens opportunities for the development of new efficiently and environmentally friendly insecticides targeting the CPLCP family of cuticular proteins.

Morphology and phylogenetic significance of the thoracic muscles in Psocodea (Insecta: Paraneoptera)

The thoracic musculature of the insect order Psocodea has been examined in only a few species of a single suborder to date. In the present study, we examined the thoracic musculature of species selected from all three suborders of Psocodea to elucidate the ground plan of the order and to examine the phylogenetic utility of the character system. The sister-group relationship between the suborders Troctomorpha and Psocomorpha received support from two novel nonhomoplasious synapomorphies, although the support from other morphological characters for this relationship is ambiguous. The sister-group relationship between the infraorders Epipsocetae and Psocetae also received support from one nonhomoplasious synapomorphy, although no other morphological characters supporting this relationship have been identified to date. The present examination revealed the potential of thoracic muscle characters for estimating deep phylogeny, possibly including interordinal relationships.

The combination of structure and material distribution ensures functionality of the honeybee wing-coupling mechanism

Fore- and hindwings of honeybees are coupled and synchronized to flap by means of a forewing posterior recurved margin (PRM) and hindwing hamuli which constitute a hook-furrow coupling. Morphological analysis shows that the PRM is composed of a thickened and sclerotized membrane with the Archimedean spiral configuration and hamuli are a set of tiny, sclerotized hooks with flexible bases. By developing a theoretical PRM model, the influence of cuticle sclerotization and membrane-thickening on a deforming pattern and maximal coupling force was comparatively simulated, indicating that the real PRM is capable of bearing the highest coupling force and the membrane thickening makes more contribution than cuticle sclerotization on augmenting the maximal coupling force that the PRM can resist. In addition, four combined strategies, i.e. the hook shape, Archimedean spiral, rich resilin concentration, and cuticle sclerotization in different parts of the whole system were proposed, and deemed to endow the honeybee wing-coupling with remarkable stability and durability to eliminate a potential structural failure of the coupling over millions of wing flapping cycles across the honeybee lifespan. This study assists us in the comprehensive understanding of the functionality of the hook-furrow wing-coupling and shows us new avenues for biomimetics of mobile coupling mechanisms in modern engineering.

Wing coupling mechanism in the butterfly Pieris rapae (Lepidoptera, Pieridae) and its role in taking off

The small white cabbage butterfly (Pieris rapae) flaps its fore- and hindwings in synchrony as the wings are coupled using a wing "coupling mechanism". The coupling mechanism of butterflies includes an enlarged humeral area located at the anterior of the hindwing base and a corresponding basal posterior part of the forewing, of which the former component dorsally contacts the ventral side of the latter one. The coupling mechanism allows for the fore- and hindwings sliding in contact along the span and chord. It is of interest that butterflies still take off successfully and fly, when their wing couplings are clipped, but they are unable to properly synchronize the fore- and hindwing motions. Compared with the regular takeoff trajectory of intact butterflies that always first fly backwards and then forwards, the coupling-clipped butterflies took off in a random trajectory. Due to the clipping of the coupling mechanism, the initiation of the hindwing flapping and the abdomen rotation from upward to downward during takeoff was postponed. The coupling-clipped butterflies changed their stroke plane in upstroke to a more vertical position and strengthened the abdominal undulation. We believe our work, which for the first time investigates the influence of coupling mechanism removal on insect flight, extends our understanding on the working principle of wing coupling in insects and its significance on the flapping flight.

Biomechanics of fore wing to hind wing coupling in the southern green stink bug Nezara viridula (Pentatomidae)

Stink bugs have wing coupling mechanisms to synchronize flapping of their wings. The wing coupling is performed through a clamp-like structure on the fore wing (i.e. hemelytron) and a rolled margin on the hind wing. Here we used modern imaging techniques to investigate structural characteristics and material composition of the wing coupling of the stink bug Nezara viridula. We found that the surfaces of the clamp-like structure and the rolled margin are covered by highly-sclerotized microtrichia, which are expected to reduce friction between the wings during flapping flight. Micro-force measurements showed that fore and hind wings can be coupled only in certain angles ranging from 40.6° to 267.7° The results further showed that the force required to uncouple fore and hind wings is maximal for a range of angles which they make with each other during flight (127.1°-238.9°). In contrast to previous observations on some other insect species, the removal of the wing coupling in stink bugs led to complete loss of flight ability. In summary, we concluded that the shape, material composition and orientation of the coupling structure guarantee a robust fore wing to hind wing coupling during flight and a fast, easy uncoupling at rest. STATEMENT OF SIGNIFICANCE: Although the coupling mechanism of insect fore wing and hind wing has long been described, the functionality of this mechanism still remains largely unknown. In the present work, using a combination of modern imaging techniques and mechanical testing, we studied the functional morphology of the fore wing-hind wing coupling mechanism of the stink bug Nezara viridula. Our study reveals the crucial role of the mechanism in the flight ability of the stink bug and sheds light on the structure-property-function relationships of the functional diptery in insects.

Structure, properties and functions of the forewing-hindwing coupling of honeybees

Worker honeybees (Apis mellifera) are morphologically four-winged, but are functionally dipterous insects. During flight, their fore- and hindwings are coupled by means of the forewing posterior rolled margin (PRM) and hindwing hamuli. Morphological analysis shows that the PRM can be connected to the hamuli, so that the fore- and hindwing are firmly hinged, and can rotate with respect to each other. In the present study, using a combination of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), we investigate the micromorphology and material composition of the coupling structures on both fore- and hindwings. High-speed filming is utilized to determine the angle variation between the fore- and hindwings in tethered flight. Using sets of two-dimensional (2D) computation fluid dynamic analyses, we further aim to understand the influence of the angle variation on the aerodynamic performance of the coupled wings. The results of the morphological investigations show that both PRM and hamuli are made up of a strongly sclerotized cuticle. The sclerotized hinge-like connection of the coupling structure allows a large angle variation between the wings (135°-235°), so that a change is made from an obtuse angle during the pronation and downstroke to a reflex angle during the supination and upstroke. Our computational results show that in comparison to a model with a rigid coupling hinge, the angle variation of a model having a flexible hinge results in both increased lift and drag with a higher rate of drag increase. This study deepens our understanding of the wing-coupling mechanism and functioning of coupled insect wings.