Areas in Argentina, Bolivia, Brazil and Paraguay were searched for the cassava mealybug, Phenacoccus manihoti Matile-Ferrero. The mealybug was located in the Paraguay River basin in the Santa Cruz de la Sierra area of eastern Bolivia, the Mato Grosso do Sul state in South-Western Brazil and in Paraguay east of the Paraguay River. Mealybug populations were extremely low in all areas but there was a period of increase from August to December. Eighteen species of natural enemies were found attacking P. manihoti: the most abundant and also most important were a solitary, internal parasitoid, Epidinocarsis lopezi (DeSantis) (Hymenoptera: Encyrtidae), Hyperaspis notata Mulsant and Diomus spp. (Coleoptera: Coccinellidae), and Ocyptamus spp. (Diptera: Syrphidae). Collections of a closely related mealybug, Phenacoccus herreni Cox & Williams yielded two additional encyrtid parasitoids, Epidinocarsis diversicornis (Howard) and Aenasius sp. nr vexans Kerrich, but they did not survive on P. manihoti. Four parasitoids (E. lopezi, E. diversicornis, Parapyrus manihoti Noyes and Allotropa sp.) and four predators (H. notata, Diomus sp., Sympherobius maculipennis Kimmins, and Exochomus sp.) were sent for quarantine. With the exception of Parapyrus manihoti, all mentioned natural enemy species were forwarded to the International Institute of Tropical Agriculture at Ibadan, Nigeria for mass rearing and subsequent release.