Rutledge Claire E, Robinson Andrew P, Eigenbrode Sanford D
Plant Soil and Entomological Sciences, University of Idaho, Moscow, ID 83844-2339, USA.
Oecologia. 2003 Mar;135(1):39-50. doi: 10.1007/s00442-002-1114-2. Epub 2003 Feb 8.
Plant features that enhance predator effectiveness can be considered extrinsic-resistance factors because they result in reduced insect herbivory. In this paper we test the hypothesis that reduced epicuticular wax (EW) in Pisum sativum L. is an extrinsic-resistance factor contributing to field resistance to Acyrthosiphon pisum (Harris). We monitored pea aphid populations in the field on reduced EW and normal EW near isolines of peas for two seasons and confirmed that aphid populations are lower on reduced EW peas than on normal EW peas. We also monitored predators within the canopies of the two pea lines to discover community level patterns in response to differences in EW. We found that while predator numbers were similar between the two lines, there were more syrphids on the normal EW peas, and a trend towards more coccinellids on reduced EW peas. We tested the impact of predators on pea aphids on the two EW lines by monitoring their population levels in cages that excluded predators, and in cages that allowed predators to enter. We found that pea aphid populations were similar on the two EW lines when predators were excluded. When predators were allowed access to the plants, pea aphid populations were reduced more on reduced EW peas than on normal EW peas. We also examined the intrinsic resistance to aphids in reduced EW peas with laboratory dual-choice tests comparing aphid response to reduced EW and normal EW peas, and found that walking, apterous aphids displayed no preference for one pea line over the other. Bioassays to measure growth and fecundity of the pea aphid on the two EW types in the greenhouse and in the field showed that intrinsic rate of increase, and other life table parameters, were not different for aphids on the two lines. Together these results support the hypothesis that reduced EW in peas is a predator-dependent extrinsic resistance factor. Genetically reducing EW bloom in peas and other waxy crop plants might improve the effectiveness of arthropod natural enemies of insect pests. More generally, the results show that a subtle change in plant morphology can substantially influence the impact of predators on insect herbivore populations. The benefit of extrinsic resistance to herbivory conferred by reduced EW may balance any benefits of a prominent EW bloom, thereby sustaining EW polymorphisms in some natural plant populations.
能够提高捕食者效能的植物特征可被视为外在抗性因素，因为它们能减少昆虫的食草行为。在本文中，我们检验了这样一个假设：豌豆（Pisum sativum L.）表皮蜡质（EW）减少是其对豌豆长管蚜（Acyrthosiphon pisum (Harris)）田间抗性的一个外在抗性因素。我们在两个生长季里，监测了近豌豆同型系中表皮蜡质减少和正常的豌豆田中的豌豆蚜种群，证实了表皮蜡质减少的豌豆上的蚜虫种群数量低于表皮蜡质正常的豌豆。我们还监测了这两种豌豆品系冠层内的捕食者，以发现对表皮蜡质差异的群落水平响应模式。我们发现，虽然两个品系间的捕食者数量相似，但表皮蜡质正常的豌豆上有更多的食蚜蝇，而表皮蜡质减少的豌豆上有瓢虫数量增多的趋势。我们通过监测排除捕食者的笼子和允许捕食者进入的笼子里的豌豆蚜种群水平，测试了捕食者对两种表皮蜡质品系上豌豆蚜的影响。我们发现，排除捕食者时，两种表皮蜡质品系上的豌豆蚜种群数量相似。当允许捕食者接触植物时，表皮蜡质减少的豌豆上的豌豆蚜种群数量比表皮蜡质正常的豌豆减少得更多。我们还通过实验室双选试验，比较蚜虫对表皮蜡质减少和正常的豌豆的反应，研究了表皮蜡质减少的豌豆对蚜虫的内在抗性，发现无翅行走型蚜虫对两种豌豆品系没有偏好。在温室和田间对两种表皮蜡质类型上豌豆蚜的生长和繁殖力进行的生物测定表明，两种品系上蚜虫的内禀增长率和其他生命表参数没有差异。这些结果共同支持了这样一个假设：豌豆表皮蜡质减少是一种依赖捕食者的外在抗性因素。通过基因手段减少豌豆和其他蜡质作物植物的表皮蜡质粉霜，可能会提高害虫节肢动物天敌的效能。更一般地说，结果表明植物形态的细微变化会显著影响捕食者对昆虫食草动物种群的影响。表皮蜡质减少赋予的对食草动物的外在抗性益处，可能会平衡显著的表皮蜡质粉霜带来的任何益处，从而在一些天然植物种群中维持表皮蜡质多态性。
