Robin J. Wootton

Quantified interference and diffraction in single Morpho butterfly scales

Brilliant iridescent colouring in male butterflies enables long–range conspecific communication and it has long been accepted that microstructures, rather than pigments, are responsible for this coloration. Few studies, however, explicitly relate the intra–scale microstructures to overall butterfly visibility, both in terms of reflected and transmitted intensities and viewing angles. Using a focused–laser technique, we investigated the absolute reflectivity and transmissivity associated with the single–scale microstructures of two species of Morpho butterfly and the mechanisms behind their remarkable wide–angle visibility. Measurements indicate that certain Morpho microstructures reflect up to 75% of the incident blue light over an angle range of greater than 100° in one plane and 15° in the other. We show that incorporation of a second layer of more transparent scales, above a layer of highly iridescent scales, leads to very strong diffraction, and we suggest this effect acts to increase further the angle range over which incident light is reflected. Measurements using index-matching techniques yield the complex refractive index of the cuticle material comprising the single–scale microstructure to be n = (1.56+0.01) + (0.06 ±0.01)i. This figure is required for theoretical modelling of such microstructure systems.

Function, homology and terminology in insect wings

Abstract. The history of current systems of wing nomenclature is summarized, and the underlying principles reviewed. The homologies of wing areas are clarified, with particular reference to the functions and positions of longitudinal lines of bending in the wings. Distinction is drawn between flexion‐lines, primarily aerodynamic in function, and fold‐lines, which are primarily concerned with wing‐folding. Of these the claval furrow ‐ a flexion‐line ‐ and the jugal fold‐line are, when recognizable, nearly constant in position, and are hence valid area boundaries and useful landmarks in vein identification. The vannal fold‐line and the median flexion‐line are variable in position, and hence unsatisfactory area boundaries. The nature and functioning of fold‐ and flexion‐lines in the axilla of Locusta are described and illustrated, and names are proposed. Conflicting aspects of commonly‐used systems of wing terminology are evaluated; and illustrated recommendations are put forward for consistent naming of veins, branches and wing areas.

Structural colour: Now you see it — now you don't

The dazzling iridescence seen in some hummingbirds and tropical butterflies arises from natural optical phenomena, the brightest of which originate in nanoscale structures that produce ultra-high reflectivity and narrow-band spectral purity. Here we investigate the coloration of male Ancyluris meliboeus Fabricius butterflies, which have patches of unusual microstructure on their ventral wing scales. We find that this highly tilted, multilayered arrangement produces a bright iridescence of broad wavelength range and generates a strong flicker contrast from minimal wing movement.

The implications of function on the origin and homologies of the dipterous wing

Abstract The origin of Diptera, and the homologies of the dipteran wing, are re‐examined in the light of recent studies on the flight biomechanics and functional wing morphology of Diptera and ofPanorpa. Significant Diptera apomorphies are identified, relevant fossils discussed, and a hypothetical wing ground‐plan figured.

Limited-view iridescence in the butterfly Ancyluris meliboeus

Few mechanisms exist in nature that effect colour reflectivity, simultaneously high in spectral purity and in intensity, over a strictly limited portion of solid angle above a surface. Fewer still bring about such colour reflectivity with an angle dependence that is distinct from the colour transition associated with conventional multilayer interference. We have discovered that the ventral wings of the butterfly Ancyluris meliboeus exhibit these optical effects, and that they result from remarkable nano-scale architecture on the wing scales of the butterfly. This nano-structure is in the form of high-tilt multilayering that, as a result of abrupt termination of the multilayers, brings about diffraction concurrently with interference. The product is bright structural colour in a limited angular region over the ventral wing surface that enables remarkably strong flicker and colour contrast through minimal wing movement. The visibility effects associated with its colour, in terms of bright and dark zones of the observation hemisphere over the wing surface, are described. We suggest the purpose of the high-contrast ventral wing visibility associated with A. meliboeus is at-rest signalling; this is distinct from the dorsal wing visibility of other species such as those of the genus Morpho, the function of which is largely for in-flight signalling.

Flight adaptations in Palaeozoic Palaeoptera (Insecta)

The use of available morphological characters in the interpretation of the flight of insects known only as fossils is reviewed, and the principles are then applied to elucidating the flight performance and techniques of Palaeozoic palaeopterous insects. Wing‐loadings and pterothorax mass total mass ratios are estimated and aspect ratios and shape‐descriptors are derived for a selection of species, and the functional significance of wing characters discussed. Carboniferous and Permian ephemeropteroids (‘mayflies’) show major differences from modern forms in morphology and presumed flight ability, whereas Palaeozoic odonatoids (‘dragonflies’) show early adaptation to aerial predation on a wide size‐range of prey, closely paralleling modern dragonflies and damselflies in shape and wing design but lacking some performance‐related structural refinements. The extensive adaptive radiation in form and flight technique in the haustellate orders Palaeodictyoptera, Megasecoptera, Diaphanopterodea and Permothemistida is examined and discussed in the context of Palaeozoic ecology.

Remarkable iridescence in the hindwings of the damselfly Neurobasis chinensis chinensis (Linnaeus) (Zygoptera: Calopterygidae)

The bright green dorsal iridescence of the hindwings of Neurobasis chinensis chinensis males, very rare in Odonata, is known to play a significant role in their courtship behaviour. The mechanism responsible for such high contrast and spectrally pure colour has been investigated and found to be optical interference, producing structural colour from distinct laminations in the wing membrane cuticle. The ventral sides of these iridescent wings are dark brown in colour. In a single continuous membrane of wing cuticle, this is an effect that requires a specialized structure. It is accomplished through the presence of high optical absorption (k = 0.13) within two thick layers near the ventral surface of the wing, which leads to superior dorsal colour characteristics. By simultaneously fitting five sets of optical reflectivity and transmissivity spectra to theory, we were able to extract very accurate values of the complex refractive index for all three layer types present in the wing. The real parts of these are n = 1.47, 1.68 and 1.74. Although there is often similarly significant dorsal and ventral colour contrast in other structurally coloured natural systems, very few system designs comprise only a single continuous membrane.

The historical ecology of aquatic insects: An overview

Abstract The fossil record of freshwater insects is reviewed. The earliest firm evidence for an aquatic habit in each relevant order is charted, together with the first appearance in time of some important component taxa. The recently expressed view that insects were primitively aquatic and apneustic is briefly discussed. It is neither confirmed nor disproved by the observed distribution of freshwater insects in time. The progressive emergence of insect life-styles in fresh water is discussed and charted. Rheobiontic forms were present in the Lower Permian, but insects may not have played much part in lentic systems before the mid-Triassic. Many early insects were predatory; but benthic periphyton scrapers and fine detritus filterers and deposit feeders may well have been present in running water at an early stage. Pelagic predators and scrapers seem to have been a Mesozoic development; and it may be that cased Trichoptera in the Cretaceous were the first significant insect shredders of coarse plant debris. The radiation of aquatic Diptera, from the Jurassic onwards, was immensely important, revolutionising the structure of many ecosystems and resulting in the colonisation of several new adaptive zones.

Geometry and mechanics of insect hindwing fans: a modelling approach

The ‘umbrella effect’, a mechanism of camber generation in the hindwing fans of orthopteroid and dictyopteroid insects, is modelled geometrically and mechanically, treating the fan as a framework whose outer margin describes a truncated logarithmic spiral. Tension in the margin compresses the radial veins, causing them to undergo Euler buckling. The model describes the distribution of compression forces in the veins around the spiral, and predicts conditions which must be met, and departures from the model expected in real wings. Actual insects fit the model and predictions quite well. The functional implications, and those of departure from the model, are discussed.

The Upper Liassic Heteroptera of Mecklenburg and Saxony

Abstract. Twenty‐seven species of Heteroptera from the Upper Liassic of Dobbertin, Mecklenburg, and East Lower Saxony are redescribed and reclassified as follows. PROGONOCIMICIDAE (= Actinoscytinidae and Eocimicidae): Progonocimex jurassicus, P.liasinus (=Eocimex liasinus); Eocercopis ancyloptera, E.similis (=Cercoprisca similis); Archicercopis falcata. ARCHEGOCIMICIDAE (= Eonabidae and Diatillidea): Archegocimex geinitzi, A.primitiva (= Eonabis primitiva), A.liadis (=Archegocoris liadis); Somatocoris conservatus; Eurynotis incisus; Progonocoris pictus; Anosmus spilopterus; Entomecoris minor; Diatillus debilis; Corynecoris semigranulatus; Macropterocoris obtusus; Ensphingocoris praerotundatus. PACHYMERIDIIDAE (= Hypocimicidae, Sisyrocoridae and Psychrocoridae): Pachymeridium dubium; Sisyrocoris rudis; Hypocimex membranaceus; Apsicoria semideleta; Cathalus alutaceus; Psychrocoris cuneifera. CUNEOCORIDAE: Cuneocoris geinitzi. NAUCORIDAE (= Apopnidae and Aphlebocoridae): Apopnus magniclavus; Aphlebocoris punctata. Infraorder Gerromorpha incertae sedis: Engynabis tenuis.