Larval characters are of importance in systematic and evolutionary studies of Diptera but lag behind characters of adults due to difficulties in obtaining relevant information. Larvae of stomach bot flies are obligate parasites completing development exclusively in the alimentary tract of equids and rhinoceroses. They possess diversified morphological adaptations, providing remarkable examples to further our understanding of larval evolution. Herein, three-dimensional structures of first instar Gasterophilus pecorum and Gyrostigma rhinocerontis are compared using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). We suggest CLSM has a large potential for exploiting cryptic character systems of micro fly larvae, as spectral range and intensity of autofluorescence emitted by sclerotized structures and soft tissues are distinct, presenting a high-contrast mechanism for multistructural visualization with non-destructive sample preparation. Five new potential synapomorphies are proposed to corroborate the sister-group Gasterophilus and Gyrostigma. The upward curving mouth-hooks of first instar Gasterophilus and Gyrostigma are distinctive in Cyclorrhapha and possibly serve to facilitate the larval subcutaneous migration within the host. Three types of mouthhooks are recognized in first instar Oestridae, with the gently curved and gradually tapered type optimized as the ancestral state, from which the gasterophiline and hypodermatine types evolved independently.

中文翻译：

---

初生马和犀牛胃蝇幼虫的三维表征（雌性：Gasterophilinae：Gasterophilus，Gyrostigma）：新颖的形态和进化意义

幼虫性状在双翅目的系统和进化研究中很重要，但由于难以获得相关信息而落后于成年性状。胃蝇的幼虫是专性寄生虫，仅在马和犀牛的消化道中完成发育。它们具有多样化的形态学适应性，为进一步理解幼虫的进化提供了杰出的例子。在此，初生幼虫Gasterophilus pecorum和Gyrostigma rhinocerontis的三维结构使用共聚焦激光扫描显微镜（CLSM）和扫描电子显微镜（SEM）进行比较。我们认为CLSM具有开发微小蝇幼虫隐性特征系统的巨大潜力，因为硬化结构和软组织发射的自发荧光的光谱范围和强度是截然不同的，这为使用非破坏性样品制备进行多结构可视化提供了高对比度的机制。提出了五个新的潜在同形来证实姐妹群Gasterophilus和Gyrostigma。第一龄幼虫Gasterophilus和Gyrostigma的向上弯曲的钩子在Cyclorrhapha中是独特的，并且可能有助于在宿主内促进幼虫皮下迁移。初生雌性三联科（Oestridae）可以识别出三种类型的嘴角，其中最适度的逐渐弯曲和逐渐渐缩的类型被优化为祖先状态，其中胃泌素和次生皮下类型从中独立进化。