The retirement services units at Massachusetts Mutual Life Insurance Company and Principal Financial Group Inc. have signed new clients.

Blue Bird Corp, Fort Valley, Ga., a bus manufacturer with 1,800 employees, has hired MassMutual to provide services for a defined benefit plan with $90 million in assets and a 401(k) plan with $65 million in assets.

Pizzagalli Construction Company, South Burlington, Vt., a commercial and industrial construction firm, has hired Principal to help run a defined contribution plan and an employee stock ownership plan.

The plans have about 800 participants and about $106 million in assets.

Hickok & Boardman Inc., Burlington, Vt., advised Pizzagalli.