Data from: Asteraceae pollen provisions protect Osmia mason bees (Hymenoptera: Megachilidae) from brood parasitism

Many specialist herbivores eat foods that are apparently low quality. The compensatory benefits of a poor diet may include protection from natural enemies. Several bee lineages specialize on pollen of the plant family Asteraceae, which is known to be a poor-quality food. Here we tested the hypothesis that specialization on Asteraceae pollen protects bees from parasitism. We compared rates of brood parasitism by Sapyga wasps on Asteraceae-specialist, Fabeae-specialist, and other species of Osmia bees in the field over several years and sites and found that Asteraceae-specialist species were parasitized significantly less frequently than other species. We then tested the effect of Asteraceae pollen on parasites by raising Sapyga larvae on three pollen mixtures: Asteraceae, Fabeae, and generalist (a mix of primarily non-Asteraceae pollens). Survival of parasite larvae was significantly reduced on Asteraceae provisions. Our results suggest that specialization on low-quality pollen may evolve because it helps protect bees from natural enemies.

诸多特化植食性昆虫均会取食表观品质低下的食物。劣质饮食所能带来的补偿性益处，或包含抵御天敌的保护效应。多个蜂类演化支特化取食菊科（Asteraceae）植物的花粉，而该科花粉被公认为品质不佳的食物来源。本研究针对“特化取食菊科花粉可帮助蜂类抵御寄生”这一假说展开验证。我们于多年间、多野外调查位点中，对比了塞蜂属（Sapyga）寄生蜂对菊科特化、野豌豆族（Fabeae）特化以及其他壁蜂属（Osmia）蜂类的子代寄生率，结果发现菊科特化蜂类的寄生频率显著低于其他类群。随后，我们通过三类花粉基质饲养塞蜂幼虫，分别为菊科花粉、野豌豆族花粉以及广谱花粉（主要由非菊科花粉混合配制而成），以此探究菊科花粉对寄生蜂的影响。实验结果显示，在菊科花粉日粮中，寄生蜂幼虫的存活率显著降低。本研究结果表明，特化取食劣质花粉的习性之所以能够演化，或因其可帮助蜂类抵御天敌。