Oh, a lot of more inexperienced guitarists I know are very comfortable with using the stock Minor Pentatonic chord box to solo, and not much else. If this is the case with you, when soloing over a song in a given major key, you can play diatonically by playing the minor pentatonic box with a root located a minor third below your original root. This is using the minor scale of the relative minor of your song's key. This let you play in a familiar pattern without going out of key. So, in G Major, like you have here, you can play in the E Minor Pentatonic Box.

How'd you get that, Dirt? --- The minor scale located a minor third below a major scale is called the major scale's relative minor. They share the same key signature. A minor third = 3 half steps. G down a minor third is G ---> F# ---> F ---> E, so E is your root for the minor pentatonic box. And to double check me, remember that E Minor is G Major's relative minor. They both contain G, A, B, C, D, E, and F#.

Hope that this helps!