Data from: Context-dependent alarm signalling in an insect

Animals often respond to danger by raising alarm to inform others. Alarm signals come in many different forms, such as visual or mechanical display, sound or odour. Some animals produce vocal alarm signals that vary with the level of danger. For chemical alarm signals, virtually nothing is known about such context-dependent signalling due to a general notion that alarm pheromones have fixed compositions. Here, we show that larvae of the Western Flower Thrips (Frankliniella occidentalis) produce an alarm pheromone whose composition varies with the level of danger they face: the presence of a relatively harmless predator or a very dangerous predator, that is either actually attacking or not. The frequency of alarm pheromone excretion increases with the level of danger. Moreover, the composition of excreted alarm pheromone varies in the relationship between total and relative amount of the putative two components, decyl acetate (DAc) and dodecyl acetate (DDAc). When pheromone is excreted with a predator present but not attacking, the percentage DDAc increases with the total amount of pheromone. When a predator does attack, however, the relationship between percentage DDAc and total amount of pheromone is reversed. Taken together, the alarm signal of thrips larvae appears to be context dependent, which to our knowledge is the first report of context-dependent composition of an alarm pheromone.动物通常会通过发出告警信号（alarm signal）向同类传递危险信息以应对威胁。告警信号形式多样，涵盖视觉展示、机械展示、声音或气味等类型。部分动物可发出随危险程度变化的语音告警信号。此前由于学界普遍认为告警信息素（alarm pheromone）组分固定不变，针对依赖情境的化学告警信号的相关研究几乎处于空白状态。本研究表明，西花蓟马（Western Flower Thrips，Frankliniella occidentalis）的幼虫会分泌告警信息素，其组分可随所面临的危险程度发生变化——危险来源包括相对无害的捕食者，以及实际正在攻击或未发起攻击的高危捕食者。告警信息素的排泄频率随危险程度升高而增加。此外，所分泌的告警信息素的组分变化，体现在其推定的两种组分——乙酸癸酯（decyl acetate，缩写DAc）与乙酸十二酯（dodecyl acetate，缩写DDAc）的总含量与相对占比的关联关系上。当捕食者存在但未发起攻击时，信息素中DDAc的占比随信息素总含量升高而增加；而当捕食者发起攻击时，DDAc占比与信息素总含量之间的关联关系则完全相反。综上，蓟马幼虫的告警信号具备情境依赖性；据我们所知，这是首项关于告警信息素组分存在情境依赖性的研究报道。