Abstract: Colonies of the banana aphid Pentalonia nigronervosa Coq. were heavily attended by ants in banana plantations on Tongatapu Island, Kingdom of Tonga. Ant-attendance reduced the density of indigenous predators of P. nigronervosa considerably. Most important was the reduction by ants of the parasitism of Aphis gossypii by the aphelinid wasp Aphelinus gossypii. The introduced aphid parasitoid Aphidius colemani was also heavily attacked by various ant species, and we conclude that ant-attendance may limit the economic impact of this successfully introduced parasitoid species.