Added: Rashawn Vaccaro - Date: 27.12.2021 13:27 - Views: 13265 - Clicks: 6253
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.
Ovipositor story on probing mechanisms of wasps is important for the understanding of the hymenopteran evolution and for the development of minimally invasive steerable probes. 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 Diachasmimorpha longicaudata 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.
From a mechanical perspective, it is very difficult to drill into a solid substrate with a very thin probe, because it can easily bend and break. The general morphology of the ovipositor is similar across all wasp ovipositor story 45 ; it consists of four elements, called valves, of which two are often merged such that three functional valves remain Fig. In most species, the distal part of the ovipositor is morphologically distinct 36which we will refer to as the tip.
However, to understand the observed diversity in the ovipositor shapes, understanding of the probing mechanics is essential. Ovipositor of D. A SEM image of the ovipositor; side view. Region shown in B is indicated with dashed lines. B A 3D reconstruction of a part of the ovipositor obtained with a micro-CT scan.
BInset Cross-section of the ovipositor showing the three valves. Buckling is a mechanical failure of a structure which occurs, for instance, when a beam cannot withstand the applied axial load and bends, possibly beyond its breaking point.
As buckling occurs more easily in slender beams, this is a real danger for parasitic wasps. Buckling depends on four parameters: i the axial load applied on the beam, ii the second moment of area of the beam, iii how well is the beam fixed on both ends i. During puncturing, axial loading of the ovipositor cannot be avoided, so only the other factors can be ovipositor story.
The second moment of area is largely determined by the diameter of the ovipositor and its wall thickness. To simplify insertion, the ovipositor must be as thin as possible, while the internal channel needs to be big enough for an egg to pass. Both of these requirements increase the chance of buckling.
In all wasps, the ovipositor is fixed internally to the reproductive system and the muscles that move the ovipositor 419so very little variance can be expected related to the fixation of the ovipositor. Some wasps protrude only a small part of the total ovipositor outside their bodies before puncturing the substrate. The part retained in the abdomen is then either strongly coiled or telescopically retracted 20 In other species, the functional length of the ovipositor is reduced by supporting it by clamping the ovipositor with parts of their hind legs 111822 or with specialized sheaths 11023 Little is known about the mechanisms parasitic wasps use for further insertion and buckling prevention of the ovipositor after the initial puncturing of the substrate.
Vincent and King 23 hypothesized a mechanism that wasps might use based on the morphology of the ovipositor Fig. In the proposed mechanism, wasps apply a pulling force on two of the three valves, which are kept stationary because of the hook-like structures on their tips function as anchors. These valves serve as guides for the third valve that is pushed inward. According to the hypothesis, buckling of the protracted valve is avoided by limiting the amplitudes of forward motion.
By alternating the protraction and retraction of the valves, the ovipositor is further inserted into the substrate, while ovipositor story excessive net push forces and axial lo that could damage the ovipositor Hypothesised insertion and steering mechanisms in 2D. Full arrows represent push forces and empty arrows pull forces.
A The push—pull mechanisms 23 only two valves are shown for clarity. C Restriction in inter-element displacements 32 causes bending due to tensile gray arrows and compression small black arrows forces modified from ref. D Arched ovipositors bend due to differential sclerotization of valve segments 34 ; see text modified from ref. E Pretension of individual elements 35 le to in-curving upon their protraction as observed in hemipteran mouthparts modified from ref.
The second challenge during oviposition is that the wasps need to steer the ovipositor tip in the direction of the desired target Proposed bending mechanisms can be divided into passive and active ones Fig. Passive bending originates from mechanical interactions of the inserted ovipositor with the substrate. Active bending occurs when bending moments originate from the relative movements of the ovipositor valves. Passive bending presumably occurs when an ovipositor has an asymmetric beveled tip Fig.
The asymmetric forces acting on such a tip push the tip away from a straight path 26 Rotation of the bevel can be used to adjust the tip direction during insertion The tips of most ovipositors across species are asymmetric 62930 and can thus potentially function as a bevel. The bevel shape can presumably be enhanced by changing the relative positions of the valves. An adjustable bevel may control the degree of bending, similar to what has been proposed for a new generation of steerable needles Three mechanisms have been proposed for active bending.
In the ovipositor story mechanism, special anatomical structures limit the motion range of individual valves 32 Bending occurs due to tension and compression in individual valves Fig. A second active bending mechanism relies on differences in valve sclerotization The distal part of ovipositors relying on this bending mechanism consists of heavily sclerotized, stiff arches, alternated with less sclerotized and flexible nodes. At rest, the arches and nodes of the dorsal ovipositor story ventral valves are aligned and the ovipositor is approximately straight.
When the ventral or dorsal valves are protracted, the arches align with nodes, which le to bending Fig. The third possible mechanism of active bending has been hypothesized for the control of hemipteran mouthparts. Similar to the ovipositors, the hemipteran mouthparts consist of multiple slender elements ovipositor story are interconnected ovipositor story and are able to slide along each other.
It is assumed that bending moments in hemipteran mouthparts originate from pre tension of the elements 35 The elements possess a certain level of inner tension and tend to curve to one side when not opposed. At rest, the elements are aligned with their tips so they counteract each other, resulting in a straight structure. When an individual element protracts, its tip curves inward toward the other elements Fig. In all three mechanisms, the amplitude of the ovipositor story and retraction of the valves probably correlates with the amount of bending and offers a way to control the curvature of the ovipositor during insertion.
The proposed theories of probing are based on morphological data, with only a few studies focusing on the ovipositor inside the substrate 2537but no one has ever analyzed the dynamics of probing inside the substrate. In this work, we aim to quantify the ovipositor use range, speed, and curvature of probing in relation to substrate density and to determine which of the proposed methods of insertion and steering are used by parasitic wasps. We do this using the species Diachasmimorpha longicaudatawhich provides an excellent example because of its long and slender ovipositor.
Extrapolation of our will also provide insight into probing and steering possibilities of other groups of parasitic hymenopterans and possibly of hemipterans and mosquitoes, as they use similar structures to probe for food. In addition, our study will add to the understanding of the functional demands acting on the ovipositor and the mechanism for drilling with slender probes. This, in turn, can be applied in the development of man-made instruments for tunneling, insertion, or probing.
We presented 28 wasps with two different gel densities and stiffnesses parameters presented in Table 1 and Fig. For details on calculations of gel parameters see SI Materials and Methods. Three wasps did not probe in both substrates. For three of the animals, the top camera recording their orientation during probing stopped working. Their data were excluded from the calculations of the range of probing, but were included in the velocity analysis.Ovipositor story
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