Smoke trail Effect particles not showing up in image render

I have created a particle system but when I try to render an image none of the particles show up. Only the plane used as emitter is rendered.

The particle circles show in 3d camera view but not when I render an image.

Have I forgotten something?

https://www.dropbox.com/s/ta1hqu2orzzubma/screen%20capture.mp4?dl=0https://www.youtube.com/watch?v=NmYYIrwTBEs