Various chalcidoid wasps can actively steer their terebra (= ovipositor shaft) in diverse directions, despite the lack of terebral intrinsic musculature. To investigate the mechanisms of these bending and rotational movements, we combined microscopical and microtomographical techniques, together with videography, to analyse the musculoskeletal ovipositor system of the ectoparasitoid pteromalid wasp Lariophagus distinguendus (Förster, 1841) and the employment of its terebra during oviposition. The ovipositor consists of three pairs of valvulae, two pairs of valvifers and the female T9 (9th abdominal tergum). The paired 1st and the 2nd valvulae are interlocked via the olistheter system, which allows the three parts to slide longitudinally relative to each other, and form the terebra. The various ovipositor movements are actuated by a set of nine paired muscles, three of which (i.e. 1st valvifer-genital membrane muscle, ventral 2nd valvifer-venom gland reservoir muscle, T9-genital membrane muscle) are described here for the first time in chalcidoids. The anterior and posterior 2nd valvifer-2nd valvula muscles are adapted in function. (1) In the active probing position, they enable the wasps to pull the base of each of the longitudinally split and asymmetrically overlapping halves of the 2nd valvula that are fused at the apex dorsally, thus enabling lateral bending of the terebra. Concurrently, the 1st valvulae can be pro- and retracted regardless of this bending. (2) These muscles can also rotate the 2nd valvula and therefore the whole terebra at the basal articulation, allowing bending in various directions. The position of the terebra is anchored at the puncture site in hard substrates (in which drilling is extremely energy- and time-consuming). A freely steerable terebra increases the chance of contacting a potential host within a concealed cavity. The evolution of the ability actively to steer the terebra can be considered a key innovation that has putatively contributed to the acquisition of new hosts to a parasitoid’s host range. Such shifts in host exploitation, each followed by rapid radiations, have probably aided the evolutionary success of Chalcidoidea (with more than 500,000 species estimated).

中文翻译：

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小黄蜂的椎骨转向

尽管缺乏椎骨固有的肌肉组织，各种小黄蜂仍可以主动地将其椎骨（=产卵器轴）转向不同的方向。为了研究这些弯曲和旋转运动的机制，我们结合显微和显微断层扫描技术以及摄像，分析了外寄生蜂 Lariophagus distinguendus (Förster, 1841) 的肌肉骨骼产卵系统及其在产卵过程中椎骨的使用情况。产卵器由三对瓣膜、两对瓣膜和雌性T9（第九腹部底板）组成。成对的第一和第二瓣膜通过 olistheter 系统互锁，允许三个部分相对于彼此纵向滑动，并形成椎骨。各种产卵器运动由一组九对肌肉驱动，其中三块（即第一瓣膜-生殖膜肌肉、腹侧第二瓣膜-毒腺储存肌肉、T9-生殖膜肌肉）首次在 Chalcidoids 中描述。第二瓣膜前部和后部-第二瓣膜肌肉的功能适应。(1) 在主动探测位置，它们使黄蜂能够拉动第二瓣膜的每个纵向分裂和不对称重叠的半部的基部，这些半部在背侧融合在顶点处，从而使椎骨横向弯曲。同时，无论这种弯曲如何，第一瓣膜都可以前移和缩回。(2) 这些肌肉还可以旋转第二瓣膜，从而旋转整个椎骨的基底关节，从而允许向各个方向弯曲。椎骨的位置固定在硬质基质中的穿刺部位（在这种情况下钻孔非常耗费能源和时间）。可自由操纵的椎骨增加了接触隐藏腔内潜在宿主的机会。主动引导椎骨的能力的进化可以被认为是一项关键的创新，被认为有助于为寄生蜂的宿主范围获得新的宿主。宿主利用的这种转变，以及随后的快速辐射，可能有助于 Chalcidoidea 的进化成功（估计有超过 500,000 个物种）。