Abstract: The currant lettuce aphid, Nasonovia ribisnigri (Mosley) is the most common aphid species on field-grown lettuce in Europe. Cultivation of lettuce varieties, resistant to the currant lettuce aphid (conferring the resistance Nr:0), was an important tool to control the infestation with N. ribisnigri in the crop, until plant resistance was broken.In 2007, a new biotype of the currant lettuce aphid was observed, which overcomes the lettuce resistance Nr:0. This biotype of N. ribisnigri is designated as biotype Nr:1. Its presence was recorded in north and central Switzerland for the first time in 2008. The dispersion of biotype Nr:1 in these parts of Switzerland was monitored using field collected aphid samples for biotests in a climate chamber. According to the results, biotype Nr:1 colonized the main lettuce production areas and also dispersed to remote sites by 2010.In comparison to susceptible lettuce, the biotype Nr:1 had lowered performance on Nr:0 resistant lettuce cultivars. Therefore, lettuce varieties conferring the Nr:0 resistance are useful to reduce the infestation by the biotype Nr:1. Although the resistance is broken, their cultivation is still recommended.