Animals, including herbivores and predators, use diet-mixing to balance their macro- and micronutrient intake. Recent work demonstrated that lady beetles fed only pea aphids from fava beans had reduced fitness caused by a deficiency of dietary sterols. However, beetles redressed this deficit by eating fava bean leaves. In the current study we used Coccinella septempunctata as a model to test the hypotheses that pea aphids are a poor sterol resource independent of their host plant, and that fava beans produce low quality prey regardless of aphid species. Additionally, we tested the reproductive rescue capacity of alfalfa and barley foliage compared to fava, and profiled the sterols of phloem exudates, foliage, and aphids reared on these different hosts. Beetle fecundity and egg viability was significantly better when provided pea aphids reared on alfalfa (compared to fava beans) and green peach aphids reared on fava plants. Alfalfa and barley leaves were not consumed by beetles and did not support beetle reproduction. The sterol profile of aphids largely reflected their host plant phloem. However, green peach aphids from fava acquired 125-times more sterol than pea aphids from fava. Our findings show how the sterol content of different host-plants can affect the third trophic level. Our results suggest that 1) prey quality varies depending on prey species, even when they occur on the same plant, 2) plant species can mediate prey quality, 3) host plant-mediated effects on prey quality partially drive omnivory, and 4) diet-mixing benefits growth and reproduction by redressing micronutrient deficits.

动物，包括食草动物和食肉动物，使用饮食混合来平衡它们的宏量和微量营养素摄入量。最近的研究表明，仅以蚕豆中的豌豆蚜虫为食的瓢虫由于缺乏膳食甾醇而导致健康下降。然而，甲虫通过吃蚕豆叶来弥补这种不足。在当前的研究中，我们使用了七星瓢虫作为一个模型来测试豌豆蚜虫是一种独立于寄主植物的贫乏甾醇资源，并且蚕豆无论蚜虫种类如何都能产生低质量的猎物。此外，我们测试了苜蓿和大麦叶子与蚕豆相比的生殖拯救能力，并分析了在这些不同宿主上饲养的韧皮部分泌物、叶子和蚜虫的甾醇。当提供在苜蓿上饲养的豌豆蚜虫（与蚕豆相比）和在蚕豆上饲养的桃蚜虫时，甲虫的繁殖力和卵活力明显更好。紫花苜蓿和大麦叶不被甲虫消耗，也不支持甲虫繁殖。蚜虫的甾醇谱在很大程度上反映了它们的寄主植物韧皮部。然而，来自蚕豆的绿桃蚜虫比来自蚕豆的豌豆蚜虫获得的甾醇高 125 倍。我们的研究结果显示了不同寄主植物的甾醇含量如何影响第三营养级。我们的结果表明 1) 猎物质量因猎物种类而异，即使它们出现在同一植物上，2) 植物物种可以调节猎物质量，3) 宿主植物对猎物质量的影响部分驱动杂食性，4) 饮食- 通过纠正微量营养素缺乏，混合有利于生长和繁殖。