Understanding the circumstances under which insect herbivores will adopt a novel host plant is a longstanding question in basic and applied ecology. While geographic variation in host use can arise through differences in both herbivore preference and plant characteristics, there is a tendency to attribute geographic variation in host use to regional differences in herbivore preference alone. This is especially true for herbivores specialized to one or a few plant species. We compared how geographic variation in herbivore preference and host plant origin shape regional differences in host plant use by the specialized herbivore, Euphydryas phaeton. In parts of its range, E. phaeton uses only a native host, Chelone glabra, while in others, it also uses an introduced host, Plantago lanceolata. We offered female butterflies from each region the non-native host plant sourced from both regions and compared their oviposition behavior. The non-native host was almost universally rejected by butterflies in the region where only the native plant is used. In the region where butterflies use both hosts, females accepted non-native plants from their natal region twice as often as non-native plants from the other region where they are not used. Acceptance differed substantially among individual butterflies within regions but not among plants within regions. Thus, both individual preference and regional differences in both the insect and non-native host contributed to the geographic variation in different ways. These results highlight that, in addition to herbivore preference, regional differences in perceived plant suitability may be an important driver of diet breadth.

了解食草昆虫在何种情况下会采用新的寄主植物是基础生态学和应用生态学中长期存在的问题。虽然寄主利用的地理差异可能是由于草食动物偏好和植物特征的差异而产生的，但有一种趋势将寄主利用的地理差异仅归因于草食动物偏好的区域差异。对于专门捕食一种或几种植物的食草动物来说尤其如此。我们比较了食草动物偏好和寄主植物起源的地理差异如何影响特化食草动物Euphyyas phaeton对寄主植物利用的区域差异。在其分布范围的部分区域，E. phaeton仅使用本地宿主Chelone glabra，而在其他区域，它还使用外来宿主车前草 ( Plantago lanceolata)。我们向来自每个地区的雌性蝴蝶提供来自两个地区的非本地寄主植物，并比较它们的产卵行为。在只使用本土植物的地区，非本土宿主几乎普遍被蝴蝶所排斥。在蝴蝶使用两种寄主的地区，雌性蝴蝶接受来自其出生地区的非本地植物的频率是来自不使用它们的其他地区的非本地植物的两倍。区域内个体蝴蝶的接受度存在显着差异，但区域内植物之间的接受度没有显着差异。因此，昆虫和非本地宿主的个体偏好和区域差异以不同的方式导致了地理变异。这些结果强调，除了食草动物的偏好之外，感知植物适宜性的区域差异可能是饮食广度的重要驱动因素。