Playing pranks on pests with plant perfumes

Abstract: The demand for alternative approaches to crop protection is growing, especially in Europe where pesticide use is becoming more restricted. To meet this demand sophisticated approaches including the use of semiochemicals need to be devised. Semiochemicals influence insect behaviour and thus have potential to disrupt pest colonisation of crops and also to attract their natural enemies. My talk gives examples of approaches used at Rothamsted to develop plant semiochemicals for IPM systems. Semiochemicals are volatile and challenging to formulate for sustained release over large areas and so we have been experimenting with delivery though the plant 1) via companion planting in push-pull systems 2) via plant activators that alter volatile emission and 3) via crop genetics. Two examples of the latter are described: plants genetically engineered to emit the aphid alarm pheromone and maize landrace lines that respond to pest oviposition by emitting volatiles that attract natural enemies. Some more fundamental considerations regarding insect recognition of host and non-host odours are discussed. Host odour recognition depends on perception of particular mixtures of volatiles as blends. Our behavioural studies have shown that responses to blends cannot be explained by responses to individual components. Furthermore the timing of exposure and background odours can influence insect responses. These complications mean that field deployment of plant semiochemicals is very challenging.