Holopainen Jarmo K
Department of Environmental Science, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland.
Bioessays. 2008 Sep;30(9):889-96. doi: 10.1002/bies.20796.
Deciduous trees remobilize the nitrogen in senescing leaves during the process of autumn colouration, which in many species is associated with increased concentrations of anthocyanins. Archetti and Hamilton and Brown observed that autumn colouration is stronger in tree species facing a high diversity of specialist aphids. They proposed a coevolution theory that the bright colours in autumn might provide an honest signal of defence commitment, thus deterring migrant aphids from settling on the leaves. So far, there have been very few experimental results to support the hypothesis, and tree commitment to phenolics-based defences has not shown direct protection against aphids. Predators and parasitoids have been found to be the major controllers of arboreal aphids. Indirect defences involve the emission of attractive volatile compounds that enhance the effectiveness of carnivorous enemies. The indirect defence hypothesis is presented to explain low aphid diversity on tree species that are green during autumn. The hypothesis suggests that green foliage can continue to produce herbivore-inducible plant volatiles and maintain volatile-based indirect plant defences against aphids until leaf abscission.
落叶树在秋季变色过程中会重新调动衰老叶片中的氮，在许多物种中，这与花青素浓度的增加有关。阿尔凯蒂、汉密尔顿和布朗观察到，在面临多种专食性蚜虫的树种中，秋季变色更为明显。他们提出了一种协同进化理论，即秋季的鲜艳颜色可能是防御能力的真实信号，从而阻止迁飞蚜虫在叶片上定居。到目前为止，很少有实验结果支持这一假设，而且树木对酚类物质防御的投入并未显示出对蚜虫的直接保护作用。已发现捕食者和寄生蜂是树栖蚜虫的主要控制者。间接防御包括释放有吸引力的挥发性化合物，以增强食肉天敌的效能。提出间接防御假说来解释秋季保持绿色的树种上蚜虫多样性较低的现象。该假说表明，绿色叶片可以持续产生食草动物诱导的植物挥发物，并维持基于挥发物的对蚜虫的间接植物防御，直到落叶。
