Data from: Hold your breath beetle – mites!

Respiratory gas exchange in insects occurs via a branching tracheal system. The entrances to the air-filled tracheae are the spiracles, which are gate-like structures in the exoskeleton. The open or closed state of spiracles defines the three possible gas exchange patterns of insects. In resting insects, spiracles may open and close over time in a repeatable fashion that results in a discontinuous gas exchange (DGE) pattern characterized by periods of zero organism-to-environment gas exchange. Several adaptive hypotheses have been proposed to explain why insects engage in DGE, but none have attracted overwhelming support. We provide support for a previously untested hypothesis that posits that DGE minimizes the risk of infestation of the tracheal system by mites and other agents. Here, we analyze the respiratory patterns of 15 species of ground beetle (Carabidae), of which more than 40% of individuals harbored external mites. Compared with mite-free individuals, infested one's engaged significantly more often in DGE. Mite-free individuals predominantly employed a cyclic or continuous gas exchange pattern, which did not include complete spiracle closure. Complete spiracle closure may prevent parasites from invading, clogging, or transferring pathogens to the tracheal system or from foraging on tissue not protected by thick chitinous layers.

昆虫的呼吸气体交换通过分支状气管系统（tracheal system）完成。充满空气的气管的入口为气门（spiracles），即外骨骼（exoskeleton）上的门状结构。气门的开闭状态决定了昆虫三种可能的气体交换模式。在静息状态的昆虫中，气门会随时间以可重复的模式开闭，由此形成不连续气体交换（discontinuous gas exchange, DGE）模式，其特征是存在一段昆虫与环境之间无气体交换的时期。学界已提出多种适应性假说以解释昆虫为何会进行不连续气体交换，但尚无一种假说获得广泛认可。本研究为一项此前未被验证的假说提供了支持：不连续气体交换可降低螨类及其他生物侵染气管系统的风险。本研究分析了15种步甲科（Carabidae）甲虫的呼吸模式，其中超过40%的个体携带外部寄生螨。与无螨个体相比，被螨侵染的个体更频繁地呈现不连续气体交换模式。无螨个体则主要采用周期性或连续性气体交换模式，该模式不包含气门的完全闭合。气门的完全闭合可阻止寄生虫侵染、堵塞气管系统，或向其转移病原体，同时也能防止寄生虫在未被厚几丁质层保护的组织上取食。