Sweetpotato weevils (family Curculionidae) are the most serious pests of sweetpotato in the world.   The Asian species, Cylas formicarius, is present in the Caribbean, southern United States, and Asia.   This stamp, one of four that illustrate insect pests, was issued March 22, 1991 by Tuvalu, a cluster of islands in the Pacific Ocean northeast of Australia.