Sebastian Büsse

Holding tight on feathers - structural specializations and attachment properties of the avian ectoparasite Crataerina pallida (Diptera, Hippoboscidae)

ABSTRACT The louse fly Crataerina pallida is an obligate blood-sucking ectoparasite of the common swift Apus apus. As a result of reduction of the wings, C. pallida is unable to fly; thus, an effective and reliable attachment to their hosts plumage is of utmost importance. The attachment system of C. pallida shows several modifications in comparison to that of other calyptrate flies, notably the large tridentate claws and the dichotomously shaped setae located on the pulvilli. Based on data from morphological analysis, confocal laser scanning microscopy, cryo-scanning electron microscopy and attachment force experiments performed on native (feathers) as well as artificial substrates (glass, epoxy resin and silicone rubber), we showed that the entire attachment system is highly adapted to the flys lifestyle as an ectoparasite. The claws in particular are the main contributor to strong attachment to the host. Resulting attachment forces on feathers make it impossible to detach C. pallida without damage to the feathers or to the legs of the louse fly itself. Well-developed pulvilli are responsible for the attachment to smooth surfaces. Both dichotomously shaped setae and high setal density explain high attachment forces observed on smooth substrates. For the first time, we demonstrate a material gradient within the setae, with soft, resilin-dominated apical tips and stiff, more sclerotized bases in Diptera. The empodium seems not to be directly involved in the attachment process, but it might operate as a cleaning device and may be essential to maintain the functionality of the entire attachment system. Highlighted Article: The avian ectoparasitic fly Crataerina pallida (Diptera, Hippoboscidae) can stay attached to its flying host, the common swift, by using a strongly modified tarsal attachment system, which provides exceptionally high attachment forces on various surfaces.

Larva, nymph and naiad – a response to the replies to Bybee et al. (2015) and the results of a survey within the entomological community

Language is often complex, inconsequent and unclear; it changes over time and evolves almost like an organism (e.g. Dorogovtsev & Mendes, 2001). However, special terminology – like scientific terminology – needs to be as clear and precise as possible. In 2015, we pointed out the varied application of the terms larva, nymph and naiad within entomology and presented an opinion piece suggesting a specified terminology for the immature stage of all insects (Bybee et al., 2015). Our paper has subsequently received three responses (Muzón & Lozano, 2016; Rédei & Štys, 2016; Sahlén et al., 2016). All responses argue for a simplification of the terminology, to call all juvenile insects larva. In our opinion, there are two obvious objectives for the application of specialized terminology: to simplify or to specify. Both objectives are logical and seek the same outcome, to clarify and end the confusion around the usage of the terms larva, nymph and naiad. Both are also based on historical usage (cf. Tillyard, 1917; Comstock, 1918). Sahlén et al. (2016) and Rédei & Štys (2016) discussed how these terms have been used over decades in textbooks and in the literature (see Sahlén et al., 2016, table 1, for a clear summary of the problem) and concur that there is indeed a lack of continuity in the use of terminology as applied to immature insects – as discussed in Bybee et al. (2015). Before moving on, there were a few statements made by Rédei & Štys (2016) and Sahlén et al. (2016) that we wish to address. Rédei & Štys (2016) argued that our opinion piece was ‘absurd’, and claimed that we asserted that scientists were not ‘well educated’ and that our terminology was ‘the correct’ terminology. We are confident that the majority of readers who read our paper will find that it is not ‘absurd’ and that it is devoid of statements that disparage entomologists or their education. We did not claim that what we were suggesting was ‘the correct’

Material composition of the mouthpart cuticle in a damselfly larva (Insecta: Odonata) and its biomechanical significance

Odonata larvae are key predators in their habitats. They catch prey with a unique and highly efficient apparatus, the prehensile mask. The mandibles and maxillae, however, play the lead in handling and crushing the food. The material composition of the cuticle in the biomechanical system of the larval mouthparts has not been studied so far. We used confocal laser scanning microscopy (CLSM) to detect material gradients in the cuticle by differences in autofluorescence. Our results show variations of materials in different areas of the mouthparts: (i) resilin-dominated pads within the membranous transition between the labrum and the anteclypeus, which support mobility and might provide shock absorption, an adaptation against mechanical damage; (ii) high degrees of sclerotization in the incisivi of the mandibles, where high forces occur when crushing the preys body wall. The interaction of the cuticle geometry, the material composition and the related musculature determine the complex concerted movements of the mouthparts. The material composition influences the strength, mobility and durability of the cuticular components of the mouthparts. Applying CLSM for extracting information about material composition and material properties of arthropod cuticles will considerably help improve finite-element modelling studies.

The head morphology of Pyrrhosoma nymphula larvae (Odonata: Zygoptera) focusing on functional aspects of the mouthparts

BackgroundThe understanding of concerted movements and its underlying biomechanics is often complex and elusive. Functional principles and hypothetical functions of these complex movements can provide a solid basis for biomechanical experiments and modelling. Here a description of the cephalic anatomy of Pyrrhosoma nymphula (Zygoptera, Coenagrionidae) focusing on functional aspects of the mouthparts using micro computed tomography (μCT) is presented.ResultsWe compared six different instars of the damselfly P. nymphula as well as one instar of the dragonfly Aeshna cyanea and Epiophlebia superstes each. In total 42 head muscles were described with only minor differences of the attachment points between the examined species and the absence of antennal muscle M. scapopedicellaris medialis (0an7) in Epiophlebia as a probable apomorphy of this group. Furthermore, the ontogenetic differences between the six larval instars are minor; the only considerable finding is the change of M. submentopraementalis (0la8), which is dichotomous in the early instars (I1,I2 and I3) with a second point of origin at the postero-lateral base of the submentum. This dichotomy is not present in any of the older instars studied (I6, middle-late and pen-ultimate).ConclusionHowever, the main focus of the study herein, is to use these detailed morphological descriptions as basis for hypothetic functional models of the odonatan mouthparts. We present blueprint like description of the mouthparts and their musculature, highlighting the caused direction of motion for every single muscle. This data will help to elucidate the complex concerted movements of the mouthparts and will contribute to the understanding of its biomechanics not in Odonata only.

On the thoracic anatomy of the Madagascan Heterogyrus milloti and the phylogeny of Gyrinidae (Coleoptera)

Gyrinidae is a group of beetles with a unique specialization of swimming on the water surface. Heterogyrus milloti Legros (Heterogyrinae) from Madagascar is a species with various preserved plesiomorphic features. The information on the morphology and biology was very limited until recently, and the thoracic anatomy remained largely unknown. Consequently, the aim of the present study is to describe external and internal thoracic features of Heterogyrus Legros in detail and to interprete them with respect to their phylogenetic and functional significance, with a special focus on the unusual flight apparatus of Gyrinidae. Characters documented with innovative techniques are compared to conditions found in other gyrinid genera and other groups of Adephaga, including characters of other body parts and larvae. A data matrix with 144 characters of adults, larvae and eggs was compiled and analysed cladistically. Gyrinidae excluding Spanglerogyrus Folkers (Heterogyrinae + Gyrininae) is supported by many apomorphies, mainly by a unique locomotor apparatus with paddle‐like middle and hind legs. The results confirm Heterogyrus as the earliest diverging branch in Gyrinidae except Spanglerogyrus, implying a sister‐group relationship between this genus and Gyrininae, a clade comprising Gyrinini, Dineutini and Orectochilini. The presence of an opening between the mesanepisternum and elytra, reduction of the lateral metafurcal arms, loss of the metathoracic M. furcacoxalis lateralis, and modifications of the head, including the dorsal shift of the upper subcomponent of the compound eyes, are synapomorphies of the three tribes. The monophyly of Gyrinini is moderately well‐supported, whereas Orectochilini is strongly supported by different characters including a highly simplified but functioning flight apparatus. A clade comprising Orectochilini and the dineutine genera is suggested by synapomorphies of adults and larvae. The monophyly of Dineutini was supported in a recent study, but not by the characters analysed here. Features of adults, larvae and eggs indicate that Gyrinidae are the sister group to the remaining adephagan families, as suggested in some earlier morphology‐based studies and recent analyses of large molecular datasets.

Bio-inspired design and movement generation of dung beetle-like legs

African ball-rolling dung beetles can use their front legs for multiple purposes that include walking, manipulating or forming a dung ball, and also transporting it. Their multifunctional legs can be used as inspiration for the design of a multifunctional robot leg. Thus, in this paper, we present the development of real robot legs based on the study of the front legs of the beetle. The leg movements of the beetle, during walking as well as manipulating and transporting a dung ball, were observed and reproduced on the robot leg. Each robot leg consists of three main segments which were built using 3D printing. The segments were combined with four active joints in total (i.e., 4 degrees of freedom) to mimic the leg movements of the beetle for locomotion as well as object manipulation and transportation. Kinematics analysis of the leg was also performed to identify its workspace. The results show that the robot leg is able to perform all the movements with trajectories comparable to the beetle leg. To this end, the study contributes not only to the design of novel multifunctional robot legs but also to the methodology for bio-inspired leg design.