Chemoreceptors help insects to interact with their environment, to detect and assess food sources and oviposition sites, and to aid in intra- and interspecific communication. In Hymenoptera, species of eusocial lineages possess large chemoreceptor gene repertoires compared with solitary species, possibly because of their additional need to recognize nest-mates and caste. However, a critical piece of information missing so far has been the size of chemoreceptor gene repertoires of solitary apoid wasps. Apoid wasps are a paraphyletic group of almost exclusively solitary Hymenoptera phylogenetically positioned between ant and bee, both of which include eusocial species. We report the chemosensory-related gene repertoire sizes of three apoid wasps: Ampulex compressa, Cerceris arenaria, and Psenulus fuscipennis. We annotated genes encoding odorant (ORs), gustatory, and ionotropic receptors and chemosensory soluble proteins and odorant-binding proteins in transcriptomes of chemosensory tissues of the above three species and in early draft genomes of two species, A. compressa and C. arenaria. Our analyses revealed that apoid wasps possess larger OR repertoires than any bee lineage, that the last common ancestor of Apoidea possessed a considerably larger OR repertoire (∼160) than previously estimated (73), and that the expansion of OR genes in eusocial bees was less extensive than previously assumed. Intriguingly, the evolution of pollen-collecting behavior in the stem lineage of bees was associated with a notable loss of OR gene diversity. Thus, our results support the view that herbivorous Hymenoptera tend to possess smaller OR repertoires than carnivorous, parasitoid, or kleptoparasitic species.

中文翻译：

---

蜂花粉的化学感受器多样性及其在蜜蜂采集花粉生活方式进化过程中的减少（膜翅目：蜂蜂亚门）

化学感受器帮助昆虫与环境相互作用，检测和评估食物来源和产卵位点，并有助于种内和种间的交流。在膜翅目中，与单独的物种相比，正常社会谱系的物种拥有大量的化学感受器基因库，可能是因为它们额外需要识别巢穴和种姓。然而，迄今为止缺少的一条关键信息是孤蜂的化学感受器基因库的大小。Apoid 黄蜂是一个几乎完全孤立的膜翅目并列群，在系统发育上位于蚂蚁和蜜蜂之间，两者都包括群居物种。我们报告了三种蜂类黄蜂的化学感应相关基因库大小：Ampulex compressa、Cerceris arearia 和 Psenulus fuscipennis。我们在上述三个物种的化学感应组织的转录组和两个物种的早期基因组草图中注释了编码气味 (OR)、味觉和离子型受体以及化学感应可溶性蛋白和气味结合蛋白的基因，A. compressa 和 C. arearia。我们的分析表明，真蜂具有比任何蜜蜂谱系更大的 OR 库，Apoidea 的最后一个共同祖先拥有比先前估计的（73）大得多的 OR 库（~160），并且在真群居蜜蜂中 OR 基因的扩展是没有以前假设的那么广泛。有趣的是，蜜蜂茎谱系中花粉收集行为的进化与 OR 基因多样性的显着丧失有关。因此，