Thank you huggybear and notthatguy for your answers I used the following workaround. http://wiki.audacityteam.org/wiki/USB_mic_on_Linux
The following ALSA configuration setting uses the default sound card as playback device (hw:0,0) and sets hw:1,0 (that suppose to be your USB-mic) to become the default capture device.
Editing the "~/.asoundrc" for a specific user
Editing the "/etc/asound.conf" for system-wide settings
Restart ALSA (after editing ): /etc/init.d/alsa-utils restart