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      Mechanisms of ovipositor insertion and steering of a parasitic wasp

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          Abstract

          <p id="d15026163e163">Using slender probes to drill through solids is challenging, but desirable, due to minimal disturbances of the substrate. Parasitic wasps drill into solid substrates and lay eggs in hosts hidden within using slender probes and are therefore a good model for studying mechanical challenges associated with this process. We show that wasps are able to probe in any direction with respect to their body orientation and use two methods of insertion. One of the methods implies a minimal net pushing force during drilling. Steering was achieved by adjusting the asymmetry of the probe’s distal end. Knowledge on probing mechanisms of wasps is important for the understanding of the hymenopteran evolution and for the development of minimally invasive steerable probes. </p><p class="first" id="d15026163e166">Drilling into solid substrates with slender beam-like structures is a mechanical challenge, but is regularly done by female parasitic wasps. The wasp inserts her ovipositor into solid substrates to deposit eggs in hosts, and even seems capable of steering the ovipositor while drilling. The ovipositor generally consists of three longitudinally connected valves that can slide along each other. Alternative valve movements have been hypothesized to be involved in ovipositor damage avoidance and steering during drilling. However, none of the hypotheses have been tested in vivo. We used 3D and 2D motion analysis to quantify the probing behavior of the fruit-fly parasitoid <i>Diachasmimorpha longicaudata</i> (Braconidae) at the levels of the ovipositor and its individual valves. We show that the wasps can steer and curve their ovipositors in any direction relative to their body axis. In a soft substrate, the ovipositors can be inserted without reciprocal motion of the valves. In a stiff substrate, such motions were always observed. This is in agreement with the damage avoidance hypothesis of insertion, as they presumably limit the overall net pushing force. Steering can be achieved by varying the asymmetry of the distal part of the ovipositor by protracting one valve set with respect to the other. Tip asymmetry is enhanced by curving of ventral elements in the absence of an opposing force, possibly due to pretension. Our findings deepen the knowledge of the functioning and evolution of the ovipositor in hymenopterans and may help to improve man-made steerable probes. </p>

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          Most cited references62

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          Design and mechanical properties of insect cuticle.

          Since nearly all adult insects fly, the cuticle has to provide a very efficient and lightweight skeleton. Information is available about the mechanical properties of cuticle-Young's modulus of resilin is about 1 MPa, of soft cuticles about 1 kPa to 50 MPa, of sclerotised cuticles 1-20 GPa; Vicker's Hardness of sclerotised cuticle ranges between 25 and 80 kgf mm(-2); density is 1-1.3 kg m(-3)-and one of its components, chitin nanofibres, the Young's modulus of which is more than 150 GPa. Experiments based on fracture mechanics have not been performed although the layered structure probably provides some toughening. The structural performance of wings and legs has been measured, but our understanding of the importance of buckling is lacking: it can stiffen the structure (by elastic postbuckling in wings, for example) or be a failure mode. We know nothing of fatigue properties (yet, for instance, the insect wing must undergo millions of cycles, flexing or buckling on each cycle). The remarkable mechanical performance and efficiency of cuticle can be analysed and compared with those of other materials using material property charts and material indices. Presented in this paper are four: Young's modulus-density (stiffness per unit weight), specific Young's modulus-specific strength (elastic hinges, elastic energy storage per unit weight), toughness-Young's modulus (fracture resistance under various loading conditions), and hardness (wear resistance). In conjunction with a structural analysis of cuticle these charts help to understand the relevance of microstructure (fibre orientation effects in tendons, joints and sense organs, for example) and shape (including surface structure) of this fibrous composite for a given function. With modern techniques for analysis of structure and material, and emphasis on nanocomposites and self-assembly, insect cuticle should be the archetype for composites at all levels of scale.
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            Host Selection by Insect Parasitoids

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              Needle insertion into soft tissue: a survey.

              Needle insertion in soft tissue has attracted considerable attention in recent years due to its application in minimally invasive percutaneous procedures such as biopsies and brachytherapy. This paper presents a survey of the current state of research on needle insertion in soft tissue. It examines the topic from several aspects, e.g. modeling needle insertion forces, modeling tissue deformation and needle deflection during insertion, robot-assisted needle insertion, and the effect of different trajectories on tissue deformation. All studies show that the axial force of a needle during insertion in soft tissue is the summation of different forces distributed along the needle shaft such as stiffness force, frictional force and cutting force. Some studies have modeled these forces. The force data in some procedures is used for identifying tissue layers as the needle is inserted or for path planning. Needle deflection and tissue deformation are major problems for accurate needle insertion and attempts have been made to model them. Using current models several insertion techniques have been developed which are briefly reviewed in this paper.
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                Author and article information

                Journal
                Proceedings of the National Academy of Sciences
                Proc Natl Acad Sci USA
                Proceedings of the National Academy of Sciences
                0027-8424
                1091-6490
                September 12 2017
                September 12 2017
                : 114
                : 37
                : E7822-E7831
                Article
                10.1073/pnas.1706162114
                5604017
                28847936
                28720a8a-db2e-4964-8758-71e1ebe35676
                © 2017
                History

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