A major hypothesis for the evolution of chemical signals is that pheromones arise from non-communicative precursor compounds. However, data supporting this hypothesis are rare, primarily because the original functions of the antecedent compounds often have been lost. A notable exception, however, is the parasitoid wasp species Leptopilina heterotoma, whose compound (−)-iridomyrmecin is used as a defensive secretion, a cue for females to avoid competition with con- and hetero-specific females, and as the primary component of the females’ sex pheromone. To better understand the evolution of sex pheromones from defensive compounds, we examined the chemical ecology of L. pacifica, the sister species of L. heterotoma. Here, we show that L. pacifica also produces a defensive secretion containing a species-specific mixture of mostly iridoid compounds. However, the composition of the secretion is more complex than in L. heterotoma, and iridomyrmecin is only a minor component. Moreover, in contrast to L. heterotoma, conspecific female competitors were not avoided by female subjects, and a role of the iridoids in the female sex pheromone of L. pacifica can be excluded, as only the females’ cuticular hydrocarbons (CHCs) resulted in the elicitation of courtship by males. Although closely related, the two sister species show substantial differences in the use of the defensive secretion for communicative purposes. Variation in pheromone usage in this genus still presents a conundrum, highlighting the need for additional studies to understand the selective forces shaping the evolution of pheromone composition.

化学信号进化的一个主要假设是信息素来自非交流前体化合物。但是，支持该假设的数据很少，主要是因为先前化合物的原始功能经常丢失。然而，一个明显的例外是拟寄生虫黄蜂物种Leptopilina heterotoma，其化合物（-）-iridomyrmecin用作防御性分泌物，为雌性提供避免与雌雄同体和异种雌性竞争的提示，并且是雌性的主要成分。女性的性信息素。为了更好地理解从防御性化合物性信息素的进化，我们研究的化学生态学L.的Pacifica，姐种L. heterotoma。在这里，我们显示出L. pacifica还会产生一种防御分泌物，其中包含大部分虹彩化合物的特定物种混合物。但是，分泌物的组成比异嗜乳杆菌中的更为复杂，而iridomyrmecin仅是次要成分。而且，与异农杆菌相比，女性受试者无法避免同种雌性竞争者的存在，且虹膜类化合物在太平洋乳杆菌的女性性信息素中的作用可以排除在外，因为只有女性的表皮碳氢化合物（CHC）才引起男性的求爱。尽管密切相关，但两个姐妹物种在防御性分泌物用于交际目的的使用方面显示出实质性差异。该属中信息素使用的变化仍然存在一个难题，突出表明需要进行更多的研究来了解影响信息素成分演变的选择性力。