Ecological studies on evolution of food plant choice by Pieris butterflies

三种小圆蝶（p.a rapaecrucivora, p.a melete和p.a napijaponica）以不同的十字花科幼虫植物为食。当雌性蝴蝶在通常食用的植物上产卵时，它要经过两个连续的步骤：(1)植物栖息地的定位和(2)植物的定位。然而，在这两个步骤中，它停止了产卵行为，而没有使用潜在的十字花科植物。粉蝶食性植物的选择主要受植物品质差和（或）寄生蜂压力的影响。然而，产卵雌虫的实际反应不受最终因素的直接影响，而受近因因素的影响。本研究阐明了每只蝴蝶的雌蝶对每一种潜在的食物植物停止产卵行为的哪一步。每只蝴蝶的栖息地都对应着其实际食用植物的集体栖息地。因此，当潜在的食物植物在Pieris物种的栖息地内时，蝴蝶可以通过植物栖息地定位的步骤，并停在植物定位的步骤上，可能是因为它们识别出了植物中的某些化学威慑物。另一方面，在植物栖息地定位的步骤中，蝴蝶停止了对无栖息地潜在食物植物的产卵行为，即使这些植物生长在邻近的地方，可能是因为它们认识到内在的障碍是近因。然而，在植物定位阶段，它们并没有进化出对这些植物的回避行为。当潜在的植物似乎处于无栖息地时，通常认为它们因为处于无栖息地而没有被利用。然而，有时没有栖息地是蝴蝶不使用潜在的食物植物的结果。

Three Pieris butterflies, P.rapaecrucivora, P.melete and P.napijaponica, used different sets of cruciferous larval food plants. When a female butterfly laid eggs on actual food plants ordinarily used, it passed through two successive steps : (1)plant habitat location and (2)plant location. However, it stoped its ovipositional behaviors at either of these steps to the potential cruciferous plants not used. The food plant choice by the Pieris butterflies were govemed by inferior plant quality and/or parasitoid pressure as the ultimate factors. However, actual response of egg-laying females is not directly affected by the ultimate factors but by the proximate ones. This study clarifies that which step females of each Pieris butterflies stop their ovipositional behaviors to each potential food plant.The habitat of each Pieris butterfly corresponded the collective habitats of its actual food plants. Therefore, when the potential food plants were in within-habitat of the Pieris species, the butterflies could pass through the step of the plant habitat location and stoped at the step of plant location, presumably because they recognized some chemical deterrents in the plant. On the other hand, the butterflies stoped their ovipositional behaviors to the potential food plants in without-habitat at the step of plant habitat location, even though those plants grew at the closely adjacent places, presumably because they recognized the intrinsic barriers as the proximate factors. However, they have not evolved avoiding behaviors to those plants at the step of plant location. When potential plants seem to be in without-habitat, it is usually considered that they are not used because of being in without-habitat. However, sometimes without-habitats were the result of the butterflies not using the potential food plants.