Spotting the invaders: A monitoring system based on plant volatiles to forecast apple fruit moth attacks in apple orchards

The exploitation of cues mediating insect-plant interactions with a view to enhance sustainable management of agroecosystems is an exciting and emergent area. Practical applications are, however, limited due to discrepancies between attraction of insects to lures in the laboratory and in the field. We hypothesised that the background odour of the crop along with the modality of release of volatiles in the field could play a role in filling the gap. Our study system comprised the apple fruit moth Argyresthia conjugella, its native host, rowan, Sorbus aucuparia, and the recurrently colonised secondary host apple, Malus communis. The attractiveness of several sources, including host plants, their collected headspaces and synthetic mimics, was measured both in the laboratory and in the field. In orchards, apple fruit moth females and males were caught in traps baited with rowan clusters. In the wind tunnel, attraction was observed when rowan (either as plant or headspace) was used as stimulus. The background from apple did not affect the attraction to the rowan odour. Whilst the response to a two-component rowan mimic decreased in the presence of an apple background, a seven-component mimic remained effective in such a background. In rowan intermast years, traps baited with this blend caught consistent numbers of moths during their migration to apple. Long lasting dispensing devices with a controlled release over the entire period of pest migration allowed a much more consistent catch of moths compared to a standard device. Results indicate that knowledge of the volatile background of the crop and of the optimisation of the dispensing device is essential when moving attractants from the laboratory or semi-laboratory environment out into the field. By considering these factors, we developed a plant volatile-based attractant to monitor the apple fruit moth and use insecticides only where and when needed. Our concept can be extended to other insect-plant interactions.