Chaplin Stephen J
Division of Biological Sciences, University of Missouri, 110 Tucker Hall, 65211, Columbia, Missouri, USA.
Oecologia. 1980 Jan;46(2):254-261. doi: 10.1007/BF00540134.
The large milkweed bug, Oncopeltus fasciatus, is a specialized seed feeder that has been observed completing nymphal development in the field on only a small proportion of its potential host species within the genus Asclepias. In central Missouri only two of the six milkweed species studied, A. syriaca and A. verticillata, commonly supported nymphal O. fasciatus growth in the field. The seed of all six species, however, was equally suitable food for bugs reared in the laboratory. In laboratory preference tests, adult bugs chose to feed on the largest seeds, A. hirtella, but such a preference could not explain the observed field feeding patterns.One explanation to account for the observed host plant selection is based upon an energetic analysis. Only A. syriaca provided enough seed biomass for a clutch of O. fasciatus nymphs to develop on a single plant, and only A. verticillata grew in high enough density that a clutch could find sufficient food within the limited range of nymphal movement. These results illustrate a corollary of the resource concentration hypothesis: within a plant group whose members share similar secondary plant chemistries, the only species that will be viable hosts for a specialized herbivore are those that provide the minimal resource density necessary for the completion of nymphal development.In central Missouri, O. fasciatus has specialized on a critical resource density, not traits of individual Asclepias species. The appearance of host selection within the potential host plant spectrum is the result of a characteristic growth form, seed output, and dispersion pattern for each milkweed species that makes some species much more likely than others to produce sufficient seed resources.
大斑蝶角蝽（Oncopeltus fasciatus）是一种专门以种子为食的昆虫，人们观察到它在野外仅在马利筋属（Asclepias）中一小部分潜在宿主植物上完成若虫发育。在密苏里州中部，所研究的六种马利筋属植物中，只有两种，即乳草（A. syriaca）和轮叶马利筋（A. verticillata），通常能在野外支持大斑蝶角蝽若虫的生长。然而，所有六种植物的种子对于在实验室饲养的虫子来说都是同样合适的食物。在实验室偏好测试中，成年虫子选择以最大的种子，即糙叶马利筋（A. hirtella）为食，但这种偏好无法解释观察到的野外取食模式。
一种解释观察到的宿主植物选择现象的观点基于能量分析。只有乳草能提供足够的种子生物量，使一窝大斑蝶角蝽若虫在单株植物上发育，并且只有轮叶马利筋生长密度足够高，以至于一窝若虫能在若虫有限的活动范围内找到足够的食物。这些结果说明了资源集中假说的一个推论：在一个其成员具有相似次生植物化学特征的植物群体中，对于一种专门的食草动物来说，唯一能够成为可行宿主的物种是那些提供若虫发育所需最低资源密度的物种。
在密苏里州中部，大斑蝶角蝽专门适应了一种关键的资源密度，而非单个马利筋属物种的特征。在潜在宿主植物范围内出现宿主选择现象，是由于每种马利筋属植物具有独特的生长形式、种子产量和分布模式，这使得某些物种比其他物种更有可能产生足够的种子资源。
