Successful host search by parasitic wasps is often mediated by host-associated chemical cues. The ectoparasitoid Holepyris sylvanidis is known to follow chemical trails released by host larvae of the confused flour beetle, Tribolium confusum, for short-range host location. Although the hexane-extractable trails consist of stable, long-chain cuticular hydrocarbons (CHCs) with low volatility, the kairomonal activity of a trail is lost two days after release. Here, we studied whether this loss of kairomonal activity is due to changes in the chemical trail composition induced by microbial activity. We chemically analyzed trails consisting of hexane extracts of T. confusum larvae after different time intervals past deposition under sterile and non-sterile conditions. GC-MS analyses revealed that the qualitative and quantitative pattern of the long-chain CHCs of larval trails did not significantly change over time, neither under non-sterile nor sterile conditions. Hence, our results show that the loss of kairomonal activity of host trails is not due to microbially induced changes of the CHC pattern of a trail. Interestingly, the kairomonal activity of trails consisting of host larval CHC extracts was recoverable after two days by applying hexane to them. After hexane evaporation, the parasitoids followed the reactivated host trails as they followed freshly laid ones. Cryo-scanning electron microscopy showed that the trails gradually formed filament-shaped microstructures within two days. This self-assemblage of CHCs was reversible by hexane application. Our study suggests that the long-chain CHCs of a host trail slowly undergo solidification by a self-assembling process, which reduces the accessibility of CHCs to the parasitoid’s receptors as such that the trail is no longer eliciting trail-following behavior.

寄生蜂成功搜索宿主通常是由宿主相关的化学线索介导的。众所周知，外寄生类 Holepyris sylvanidis会追踪由混淆的面粉甲虫Tribolium confusum的寄主幼虫释放的化学痕迹，用于短程寄主定位。尽管己烷可萃取的痕迹由稳定的、低挥发性的长链表皮碳氢化合物 (CHC) 组成，但在释放两天后，痕迹的凯罗莫纳活性就会消失。在这里，我们研究了这种开罗单胞菌素活性的丧失是否是由于微生物活动引起的化学痕迹成分的变化。我们化学分析了由T. confusum己烷提取物组成的痕迹在无菌和非无菌条件下沉积不同时间间隔后的幼虫。GC-MS 分析表明，无论在非无菌或无菌条件下，幼虫踪迹的长链 CHCs 的定性和定量模式都不会随时间发生显着变化。因此，我们的研究结果表明，宿主路径的 kairomonal 活性的丧失不是由于微生物引起的路径 CHC 模式的变化。有趣的是，由宿主幼虫 CHC 提取物组成的小径的开罗单胞菌活性在两天后通过对它们应用己烷可恢复。己烷蒸发后，寄生蜂跟随重新激活的宿主轨迹，因为它们跟随新铺设的宿主轨迹。冷冻扫描电子显微镜显示，这些痕迹在两天内逐渐形成丝状微结构。这种 CHCs 的自组装通过己烷应用是可逆的。我们的研究表明，宿主路径的长链 CHC 通过自组装过程缓慢固化，这降低了 CHC 对寄生蜂受体的可及性，因此路径不再引发跟踪行为。