Pallini A, Janssen Arne, Sabelis Maurice W
Institute for Systematics and Population Biology, University of Amsterdam, The Netherlands fax: (31) 20 5257754; e-mail:
Oecologia. 1997 Apr;110(2):179-185. doi: 10.1007/s004420050147.
Plants under herbivore attack produce volatiles, thus attracting natural enemies of the herbivores. However, in doing so, the plant becomes more conspicuous to other herbivores. Herbivores may use the odours as a cue to refrain from visiting plants that are already infested, thereby avoiding competition for food, or, alternatively, to visit plants with defences weakened by earlier attacks. We investigated the response of one species of herbivore (the spider mite Tetranychus urticae) to odours emanating from cucumber plants infested by conspecific or heterospecific (the western flower thrips, Frankliniella occidentalis) herbivores. Olfactometer experiments in the laboratory showed that spider mites have a slight, but significant, preference for plants infested with conspecifics, but strongly avoid plants with thrips. These results were substantiated with greenhouse experiments. We released spider mites on the soil in the centre of a circle of six plants, half of which were infested with either conspecifics or heterospecifics (thrips), whereas the other half were uninfested. It was found that 60-70% of the mites were recaptured on the plants within 5 h after release. Results of these experiments were in agreement with results of the olfactometer experiments: (1) significantly fewer spider mites were found on plants infested with thrips than on uninfested plants and (2) more mites were found on plants with conspecifics than on clean plants (although this difference was not significant). From a functional point of view it makes sense that spider mites prefer clean plants over thrips-infested plants, since thrips are not only competitors, but are also known as intraguild predators of spider mites. Possible reasons for the slight attraction of spider mites to plants infested with conspecifics are discussed.
遭受食草动物攻击的植物会产生挥发性物质，从而吸引食草动物的天敌。然而，这样做会使植物对其他食草动物来说更加显眼。食草动物可能会利用这些气味作为线索，避免去拜访已经受到侵害的植物，从而避免食物竞争，或者，也可能会去拜访那些因早期攻击而防御能力减弱的植物。我们研究了一种食草动物（二斑叶螨）对黄瓜植株散发的气味的反应，这些黄瓜植株被同种或异种（西花蓟马）食草动物侵害。实验室中的嗅觉测定实验表明，二斑叶螨对受到同种侵害的植物有轻微但显著的偏好，但强烈避开有蓟马的植物。温室实验证实了这些结果。我们在由六株植物围成的圆圈中心的土壤上释放二斑叶螨，其中一半植物受到同种或异种（蓟马）侵害，而另一半未受侵害。结果发现，释放后5小时内，60%-70%的螨虫在植株上被重新捕获。这些实验结果与嗅觉测定实验结果一致：（1）在有蓟马侵害的植株上发现的二斑叶螨明显少于未受侵害的植株；（2）在有同种侵害的植株上发现的螨虫比在未受侵害的植株上更多（尽管这种差异不显著）。从功能角度来看，二斑叶螨更喜欢未受侵害的植株而不是有蓟马侵害的植株是有道理的，因为蓟马不仅是竞争者，而且还是已知的二斑叶螨的集团内捕食者。文中讨论了二斑叶螨对受到同种侵害的植物有轻微吸引力的可能原因。
