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.

诸多专食性植食动物取食表观上属于"低质量"的食物。劣质食源带来的补偿性益处或许包括抵御天敌的保护作用。多个蜂类演化支特化取食菊科（Asteraceae）植物的花粉，而菊科花粉被认为是低质量的食源。本研究针对"特化取食菊科花粉可保护蜂类免受寄生"这一假说开展了验证。我们在多年间、多地点的野外环境中，对比了脊腹蜂属（Sapyga）胡蜂对三类切叶蜂属（Osmia）物种的子代寄生率：特化取食菊科花粉者、特化取食野豌豆族（Fabeae）花粉者，以及其他切叶蜂物种，结果发现特化取食菊科花粉的蜂类，其被寄生的频率显著低于其他类群。随后，我们通过三种花粉基质饲养脊腹蜂幼虫——分别为菊科花粉混合物、野豌豆族花粉混合物，以及广谱花粉混合物（以非菊科花粉为主的混合花粉）——以此验证菊科花粉对寄生者的作用。以菊科花粉为食的寄生幼虫，其存活率显著降低。本研究结果表明，特化取食低质量花粉的习性之所以能够演化，或许是因为该习性可帮助蜂类抵御天敌。