Identification of walnut husk (Juglans regia L.) volatiles and the behavioural response of the invasiveWalnut Husk Fly, Rhagoletis completa Cresson

Abstract
BACKGROUND: Several European countries are important walnut (Juglans regia L.) producers. However, these countries must
contendwith the recent introduction of theWalnut Husk Fly,Rhagoletis completa Cresson (Diptera, Tephritidae),which is causing
severe economic losses, especially in organic production. Because most Tephritid fruit flies use kairomones in their search for
host plants, we hypothesise that this highly specialist species orients toward the volatile blend released by walnut husks.
RESULTS:We collected, identified, and quantified the volatile organic chemicals (VOCs) released by walnut husks from themost
commonly cultivated variety in France (Franquette). Then, the behavioural response of R. completa toward synthetic odour
blends was recorded in dual choice assays conducted in net cages. A total of 26 VOCs were identified, with 𝜶-pinene, 𝜷-pinene,
trans-linalool, eugenol, and tetradecane representing the major constituents. In the dual choice assay, male and female R.
completa were strongly attracted to synthetic blend that includedmost of the identified husk VOCs.
CONCLUSION:When searching for a host plant, R. completa use host fruit kairomones. The potential of these semiochemicals in
monitoring andmanagement of this quarantine pest is discussed.