Miniaturization is a major evolutionary trend prominent in insects, which has resulted in the existence of insects comparable in size to some unicellular protists. The adaptation of the complex antennal multisensory systems to extreme miniaturization is a fascinating problem, which remains almost unexplored. We studied the antennal sensilla of Scydosella musawasensis Hall, 1999 (Coleoptera: Ptiliidae), the smallest free-living insect, using scanning electron microscopy. The antenna of S. musawasensis bears 131 sensilla; no intraspecific variation in the number or position of the sensilla has been revealed. Nine different morphological types of sensilla are described according to their external morphological features and distribution: four types of sensilla trichodea, one type of sensilla chaetica, two types of sensilla styloconica, and two types of sensilla basiconica. Morphometric analysis of the sensilla of S. musawasensis, based on measurements of the lengths and diameters of sensilla and their location and number, showed the absence of significant differences between females and males. Comparative allometric analysis of S. musawasensis and larger Coleoptera showed that the number of sensilla and the size of sensilla chaetica decrease with decreasing body size. However, the number of the types of sensilla and the length and diameter of the multiporous sensilla basiconica revealed no correlation with the body size. Comparison of the acquired data with the results of our earlier study of the antennal sensilla of some of the smallest parasitic wasps is used to put forward hypotheses on the common principles of miniaturization of the antennal sensory systems of insects.

中文翻译：

---

最微小的感觉：最小的自由生活昆虫 Scydosella musawasensis（鞘翅目：Ptiliidae）的触角感受器


小型化是昆虫中突出的主要进化趋势，这导致了与一些单细胞原生生物大小相当的昆虫的存在。复杂的触角多感官系统适应极端小型化是一个令人着迷的问题，但几乎尚未被探索。我们使用扫描电子显微镜研究了最小的自由生活昆虫 Scydosella musawasensis Hall, 1999（鞘翅目：Ptiliidae）的触角感器。 S. musawasensis 的触角有 131 个感器；尚未发现感器数量或位置的种内差异。根据感器的外部形态特征和分布，描述了九种不同的形态类型：毛感器四种类型，毛感器一种，柱锥感器两种，基本感器两种。基于对感器的长度和直径及其位置和数量的测量，对穆萨瓦链鼠的感器进行了形态计量学分析，结果表明雌性和雄性之间不存在显着差异。对Musawasensis和较大鞘翅目的异速生长比较分析表明，随着体型的减小，感器的数量和毛感器的尺寸也随之减少。然而，感器种类的数量以及多孔基本感器的长度和直径与体大小没有相关性。将获得的数据与我们早期对一些最小的寄生黄蜂触角感觉器的研究结果进行比较，用于提出关于昆虫触角感觉系统小型化的共同原理的假设。