The vinegar fly Drosophila suzukii (Matsumura) (Diptera Drosophilidae), spotted wing drosophila, is a new invasive fruit pest that recently became established in Europe. Unlike other fruit flies that typically only infest overripe and rotten fruit, D. suzukii females oviposit in ripe fruit leading to considerable economic losses of fruit during production. In 2011 and 2012 D. suzukii was detected at several places in Belgium. In 2013, a large-scale monitoring in frame of the project "FLY ALERT" (FOD) was executed using traps with liquid attractant (apple cider vinegar) at more than 100 locations across Belgium during the whole fruit growing season. At 16 locations we also compared the efficacy of a 'bottle type' trap with a 'cup type' trap. The results show that D. suzukii has expanded its distribution in Belgium. Remarkably, in 2013 as well as in 2012 the first detections were made only in the second part of the growing season (August) and the populations reached their peak only at the very end of the season (November). In the bottle type trap the first flies were caught 2-3 weeks earlier than in the cup type trap. In addition, also the population peaks were on average 1 week earlier when monitored with the bottle trap compared to when monitored with the cup trap. In 2014, after an exceptional mild winter adult D. suzukii flies were continuously detected throughout the winter and early spring. The implications of these findings for the phenology of D. suzukii in the Northwest climate region of Europe are discussed.