The biology of the weevilCoelocephalapion aculeatum(Fall) and its specificity toMimosa pigraL. (Mimosaceae), a serious introduced weed in Australia and Thailand, were studied in a quarantine facility in Australia. Ninety-two plant species were screened, andM. pigrawas the only host that sustained a population ofC. aculeatum.Adults fed on developing and open inflorescences and oviposited mainly in buds of inflorescences of mid-to-late development. Larvae developed and pupated within these buds. Developmental time from egg to adult was 10–12 d. Field releases commenced in July 1991 in Thailand and in January 1992 in the Northern Territory of Australia.