A new apionine weevil, Coelocephalapion gandolfoi, new species, from Argentina and Chile is described and illustrated. The new species belongs to the C. frontellum species group and is especially close to the North American species C. frontellum (Fall), C. subornatum (Fall) and C. tellum Kissinger. Coelocephalapion gandolfoi has been associated with the pods or plants of the following species of Prosopis L. (Fabaceae): P. alba (Grisebach), P. alpataco Philippi, P. caldenia Burkart, P. chilensis (Molina), P. flexuosa DC, P. nigra (Grisebach), and P. ruscifolia (Grisebach). It is under investigation as a potential biocontrol agent for invasive Prosopis species in South Africa.