to pick up inserted serial port portname

Incidentally, if you feel the WMI approach is a bit 'heavy' for your requirement, then a cruder but much simpler approach would be to poll the SerialPort.GetPortNames method every second or so using a timer to see if there have been any changes to the string array which it returns:

http://msdn.microsoft.com/en-us/library/system.io.ports.serialport.getportnames(v=vs.110).aspx

Well, it's possible to do stuff like this using WMI events but not easy.

Fortunately, there's some code in this thread:

http://stackoverflow.com/questions/4199083/detect-serial-port-insertion-removal