Ecological studies on evolution of food plant choice by Pieris butterflies

菜粉蝶(P.rapaecrucivora)、甜粉蝶(P.Melete)和油菜粉蝶(P.napiJapan onica)这三种蝴蝶使用了不同的十字花科幼虫食物植物。当一只雌性蝴蝶在实际使用的食用植物上产卵时，它经历了两个连续的步骤：(1)植物栖息地定位和(2)植物定位。然而，在这两个步骤中的任何一个步骤，它都停止了对潜在的十字花科植物的产卵行为。黑粉蝶对食物植物的选择主要受植物品质差和(或)寄生压力的制约。然而，产卵雌性的实际反应并不直接受到最终因素的影响，而是受到最近因素的影响。这项研究阐明了每只斑潜蝶的雌性阶梯停止产卵行为，每只斑潜蝶的栖息地与其实际食料植物的集体生境相对应。因此，当潜在的食用植物处于Pieris物种的栖息地内时，蝴蝶可以通过植物栖息地的步骤而在植物位置的步骤处停留，这可能是因为它们识别出植物中的一些化学威慑物质。另一方面，蝴蝶在植物栖息地的位置停止了对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最接近的因素。然而，它们并没有进化出在植物定位阶段对这些植物的回避行为。当潜在植物似乎没有栖息地时，人们通常认为它们没有被利用，因为它们没有栖息地。然而，有时没有栖息地的蝴蝶是因为没有利用潜在的食物植物。

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.