A one-piece applicator device for applying a fluid or pasty product to keratin fibres includes a core that extends along a longitudinal axis XX and at least one flexible stem that is embedded at at least a first and a second point along the longitudinal core, the stem extending substantially along the longitudinal axis XX, spikes being provided on the core and/or on the at least one stem. The core is provided with at least one through-opening and the at least one flexible stem extends substantially in a radial plane and has at least a first and a second curve along its length, such that the stem crosses the at least one opening without contact in order to ensure mobility in a radial plane of the device.