At how much income can colonial nations self expand?

Question

I have a colonial nation at La Plata but it doesn't self expand. Reading the EU4 wiki, it reads

When colonial nations have enough income to sustain a working colonist, they will automatically colonize uncolonized land adjacent to them.

But what is that income threshold?

Answer 1

They need to have enough income to sustain the maintenance cost of the colonist, which is at least 2 ducats per month.