植物病原体通过改变宿主植物的气味来吸引昆虫媒介，图右为被病菌感染的苹果。
根据《化学生态学杂志》上发表的一项新的研究结果，为了吸引昆虫媒介，植物病原体Candidatus Phytoplasma mali（Candidatus植原体）改变了植物的气味，从而确保这一传染过程能够得到最大的传播。研究人员认为，这一发现将有助于研制出新的植物抗虫方法。
苹果增生病——能够导致严重的经济损失——是由Ca. P. mali引发的，它的特点是使植物的枝丫看起来就像女巫的扫帚，并结下小而无味的果实，这些果实根本就无法出售。细胞壁较少的细菌Ca. P. mali在被感染的植物的韧皮部生长，并且由以韧皮部为食的木虱所传播。这些木虱在苹果树上繁殖，而新孵化出的成虫通过食用被感染的植物韧皮而携带上Ca. P. mali。对植物种间外激素——由活的有机体分泌并释放的化学物质，有利于接收者而不利于供体——的嗅觉响应之前被认为对于木虱寻找宿主的行为是至关重要的。在这项最新的研究中，被感染以及未被感染的昆虫的行为与被感染和未被感染的苹果树之间的关系是研究的重点。
德国吉森大学的Mayer CJ与同事针对行为的生物测定使用了一种Y型嗅觉计，从而记录昆虫对未被感染以及被感染的苹果树枝丫气味的响应。木虱被放入嗅觉计，用来测定它们是否会选择放有被感染或未被感染的嫩枝的仪器臂。研究人员通过PCR证实了昆虫被感染的状态，而学生t检验则被用来确定这些结果在统计学上是否具有意义。
这项研究的主要意义在于发现被感染的苹果树能够明显吸引被感染以及未被感染的昆虫。病原体的好处在于未被感染的昆虫将最终被感染，而已经被感染的昆虫则将吃下更多的病原体，从而增加一棵未被感染的树最终被感染的可能性。那些在被感染的苹果树上繁殖却未被Ca. P. mali感染的木虱具有相反的响应，并且遭到被感染的植物的抵制，这使作者推测，被Ca. P. mali感染或许也能够影响昆虫的行为。
利用气相色谱—质谱联用分析仪能够测定苹果树释放的化学物质。与未被感染的植物相比，被感染的苹果树能够产生更多的倍半萜烯β-丁香烯，同时研究人员已经证明，木虱能够直接被β-丁香烯所吸引。（生物谷Bioon.com）
生物谷推荐原始出处：
Journal of chemical ecology，34(12):1518-22，Mayer CJ，Gross J
Pathogen-induced Release of Plant Allomone Manipulates Vector Insect Behavior.
Mayer CJ, Vilcinskas A, Gross J.
Institute for Phytopathology and Applied Zoology, Justus-Liebig University, Giessen, 35392, Germany.
Infochemicals mediate communication within and between different trophic levels. In this study, we identified a new type of plant allomone induced by a plant pathogen and perceived by its vector insect Cacopsylla picta. This phloem-feeding psyllid is the main vector of Candidatus Phytoplasma mali, a cell wall-lacking bacterium that causes the so-called apple proliferation disease. In a previous study, we showed that newly emerged females of C. picta were attracted by the odor of phytoplasma-infected apple plants (Malus domestica), which release ss-caryophyllene in contrast to uninfected plants. Here, the attractiveness of this sesquiterpene for C. picta was confirmed in both olfactometer bioassays and field studies. Synthetic ss-caryophyllene was highly attractive to newly emerged adults of C. picta both when offered simultaneously with healthy apple odor and without. The psyllid's response was independent of its odor experience and infection status. These results confirm our previously established hypothesis that this phytoplasma manipulates the behavior of its vector insect by changing the odor blend of its host plant. Deployed in apple orchards, sticky traps baited with ss-caryophyllene dispensers caught both males and females of C. picta. Consequently, this new type of infochemical, i.e., a phytopathogen-induced plant allomone, represents a promising compound to develop innovative techniques for monitoring or maybe even mass trapping of C. picta.
