Insect taxi by fragrance manipulation

Pathogens change the smell of apple trees to attract insects as a carrier

Summer apple leaf suckers, Cacopsylla picta, transfer the phytoplasmas © Julius Kühn-Institut
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The manipulation and attraction of conspecifics or helpful members of other species by certain odors is an old hat from the box of tricks of Mother Nature. Nevertheless, the tactic of the pathogen of the apple shoot addiction astonishes: Infestation by the germ alters the smell of the apple tree, thereby attracting insects sucking in juice. This in turn uses the pathogens as a taxi to the next apple tree.

Phytoplasmas are plant pathogenic bacteria without a cell wall, which, like viruses, only grow in living host tissue. They are transmitted by insects. Their own metabolism is so greatly reduced that vital bio-molecules have to be imported from the host cells. More than 700 plant diseases are caused by phytoplasmas, but the thing has a catch: Phytoplasma alone can not infect plants. They depend on insects as a means of transport.

Infested apple trees smell different

As scientists of the Julius Kühn Institute (JKI) in Dossenheim have now found out, the pathogen of the apple shoot addiction, Candidatus Phytoplasma mali, manipulates the smell of the infected apple trees in order to attract a very specific type of insect. "In the course of evolution, a very special interaction has developed between the apple shoot addiction phytoplasma, its host, the apple, and its transmitter, " explains Jürgen Gross. The scientist from the Julius Kühn-Institut has been working with his team for some time on phytoplasmas that trigger apple-craving and on their infection pathways. As early as 2005, he showed that the summer apple leaf aspirator reacts to certain chemical signals of the apple trees.

Modified scent attracts leaf suckers

"However, recent studies in olfactory laboratory experiments have shown that the phytoplasmas change the smell of their infected apple trees to make them more attractive to certain stages of leaf sucking, " says Gross. Gas chromatographic analysis of the fragrances released from the apple trees showed that only in the phytoplasma-infected trees increased ß-caryophyllene was formed. Young summer apple leaf aspirants prefer this smell and prefers to infect infected apple trees. With this the bacterium has reached its goal. It has called a suitable taxi, which will take him to the next apple tree.

Approach to combat

In laboratory and field experiments on the subject was also examined whether not another well-known Blattlosaugerart contributes to the spread of Apfeltriebsucht. This assumption was not confirmed, as these leaf suckers use hawthorn as a preferred host plant for propagation and carry only small amounts of the bacterium in itself. Hawthorn is not infected by the bacterium and thus represents a dead end for further distribution dar. Display

"Now that we already know some of the smelling preferences of the insect insects, we can take advantage of this knowledge to prevent the spread of apple addiction in the future, " says Gross, He and his coworkers now want new ones against the background of these results

To develop Bek mpfungsstrategien, and catch the leaf suckers by means of odor traps or keep away by means of deterrent substances from the Apfelb umen.

(Julius K hn Institute, 28.07.2009 - NPO)