The role of volatiles in the communication of plants

Insects have beneficial as well as harmful effects in plants. Pollination for example is a tremendously important process that determines yield in many different crops. Although we know that insects are attracted to flowers with an array of metabolic cues such as colour, fragrance and nectar, hardly anything is known about how crucial these metabolic cues are for crop yield. Vice versa, protection of crops against insects can use either direct host plant resistance or biological control, and also here plant metabolism is crucial. These two approaches are fundamentally different in that host plant resistance depends on direct defence traits of the crop plants (such as trichomes, toxic secondary metabolites or proteins, and repellents), whereas biological control depends on antagonists or enemies of the pest organisms. For the latter it is crucial that the biological control agents are able to find their prey. Hereto, plants – upon herbivory - produce volatiles that are attractive to the natural enemies of the herbivore. The use of predators and parasitoids for biological control is receiving more and more attention and for many years it has been common practice in a number of crops in glasshouse as well as open fields. We are interested in the role of terpenes and other volatiles, and their biosynthesis, in this indirect as well as in direct defence in sweet pepper, cucumber and Citrus. We study the molecular and biochemical consequences of the engineering and the effects on the behaviour of natural enemies as well as pest insects. With support of the EU we will investigate the role of volatile and non-volatile metabolites in the resistance of Citrus against the psyllid vectors of Huanglongbin.