Brewery yeast waste was converted by heat and enzyme treatment into a protein bait that was found to be highly attractive to adult pest fruit flies (Diptera: Tephritidae) in Vietnam. Two large area field control trials were then carried out using the protein bait mixed with fipronil insecticide and applied weekly as a low volume spot spray to the foliage. The first trial was conducted in north Vietnam in over 35 ha of peach (Prunus persica L.) that was severely infested by Bactrocera pyrifoliae and B. dorsalis. The second trial was conducted in the Mekong Delta on over 50 ha of Barbados cherry (Malpighia glabra) that was severely damaged by B. correcta and B. dorsalis. In the peach crop the protein bait spot sprays reduced the damage to less than 5 per cent in one season compared with 100 per cent fruit damage in the control (untreated) area. In the Barbados cherry crop, protein bait spot sprays reduced the damage to less than 4 per cent compared with over 70 per cent damage to fruits in the control (untreated) area. As a result of the huge reductions in fruit fly damage, highly significant increases in peach and Barbados cherry yields have been obtained leading to a 4-fold increase in income for peach farmers and a 2-fold increase in income for Barbados cherry farmers. These trials have demonstrated the high efficacy of protein bait + fipronil bait sprays for effective control of pest fruit flies in Vietnam.