Evaluation of hop (Humulus lupulus) as a repellent for the management of Drosophila suzukii

Over the past decade, the spotted-wing drosophila, Drosophila suzukii Matsumara has become one of the most important pests of soft- and stone fruits throughout Europe. Currently, the majority of growers still rely heavily on a limited portfolio of chemical foliar spray insecticides. Alternative strategies such as attract and kill (pull) or behavioral control systems that repel or deter D. suzukii from damaging fruits (push) are less common. We evaluated the potential of hop (Humulus lupulus L.), as a repellent for the Integrated Pest Management of D. suzukii, in controlled greenhouse conditions as well as at commercial field sites. In greenhouse cage tests on fruit or attractant medium, the positive controls thymol and 1-octen-3-ol as well as certain hops significantly reduced larval infestation levels compared to an untreated control, while other hop products showed only numerical reduction in infestation. A controlled field trial on raspberries (Rubus idaeus L.) failed to replicate these results, both for the positive control repellents as for the hop samples. In field experiments in commercial raspberry and blackberry (Rubus fruticosus L.) plantations, no significant reduction in oviposition or differences in population density could be observed for the hop treated plots as compared to the untreated. Through SPME headspace analysis of the hops, a number of compounds were associated with the efficacy observed in the greenhouse, even though different hop varieties were found to have notably different volatile profiles.