In 1996, a majority (61%) of 190 sapodilla farmers in the Mekong Delta, Vietnam considered the black ant, Dolichoderus thoracicus (Smith), beneficial in decreasing damage by the fruit borer Alophia sp. (51%), the mealybug Planococcus lilacinus (Cockerell) (43%), and "bad" ants, notably Cardiocondyla wroughtoni (Forel) (38%). A significantly greater proportion of orchards in Can Tho had D. thoracicus (60%) than orchards in Tra Vinh (42%) (P < 0.05). In orchards where D. thoracicus were present, 25% fewer farmers sprayed insecticides than in orchards without D. thoracicus. Promoting greater farmers' acceptance of D. thoracicus may be difficult because 30% of the farmers said that D. thoracicus increases mealybug populations. The influence of D. thoracicus on both Alophia sp. and P. lilacinus infestations was tested in both provinces in 1996 and 1997. The mealybug P. lilacinus was not affected, but Alophia sp. damage was significantly smaller in ant-abundant trees (P < 0.01). In Tra Vinh, the use of high-pressure pumps to spray tree canopies with water hampered D. thoracicus and lessened Alophia sp. control. Farmer-to-farmer training and mass media campaigns about the beneficial effect of D. thoracicus should be conducted to promote wider use of this ant species as a biological control agent and to reduce pesticide use in sapodilla orchards.