Maybe Gwen Stefani should take main squeeze Blake Shelton on the road with her, because concert ticket sales for her summer tour are “horrifying,” a music source said.

Stefani’s “This Is What the Truth Feels Like” tour was announced on April 18 and opens in Boston on July 12. But aside from her Jones Beach and Los Angeles shows, No Doubt’s former frontwoman hasn’t gained traction with ticket buyers — despite scoring her first No. 1 solo album in March.

The one-time judge on “The Voice” confronts what every touring act dreads before hitting the road, the source said — a sea of blue (the color for unsold seats) on Ticketmaster’s interactive seat map for each tour stop, interrupted by an occasional red dot signifying a resale seat.

Stefani’s representatives didn’t respond when asked to comment. Live Nation had no comment.