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.

多数特化植食性昆虫会取食表观质量不佳的食物。这类劣质食物所能带来的补偿性益处，其中一项便是帮助宿主抵御天敌。多个蜂类支系特化取食菊科（Asteraceae）植物的花粉，而该科花粉素来被视作质量低下的食物来源。本研究针对“特化取食菊科花粉可保护蜂类免受寄生”这一假说展开验证：我们在多年间、多野外位点中，对比了褶翅小蜂属（Sapyga）对菊科特化、野豌豆族（Fabeae）特化以及其他切叶蜂属（Osmia）蜂种的子代寄生率，结果发现菊科特化蜂种的寄生率显著低于其他蜂类类群。随后，我们通过将褶翅小蜂幼虫饲养于三种花粉饲料中（分别为菊科花粉饲料、野豌豆族花粉饲料，以及以非菊科花粉为主混合制成的广谱花粉饲料），验证了菊科花粉对寄生生物的影响，结果显示在菊科花粉饲料组中，寄生幼虫的存活率显著降低。本研究结果表明，特化取食劣质花粉这一习性之所以能够演化，或许是因为其能够帮助蜂类抵御天敌。