Simple SummaryThis study examined the occurrence, biological characteristics, and effectiveness of the parasitoid waspAcerophagus papayaeNoyes and Schauff in controlling the papaya mealybugParacoccus marginatusWilliams and Granara de Willink, a major pest of cassava crops in Vietnam. The results showed thatA. papayaenaturally occurred more frequently than other species of parasitoid wasps. The honey solution was found to be important for increasing the lifespan ofA. papayaein the absence of hosts. The second instar of the mealybug was found to be the most suitable host stage for parasitism byA. papayae. Female wasps can produce a large number of eggs during their entire lives. These findings suggest thatA. papayaecould be an effective agent for controllingP. marginatusand improving crop pest management not only in Vietnam, but in other regions as well.AbstractCassava is a valuable export commodity crop that is often attacked by pests, causing economic losses for this crop. The papaya mealybugParacoccus marginatushas become a major pest of cassava in Vietnam. The parasitoid waspAcerophagus papayaehas been demonstrated to be the most efficient parasitoid wasp for controllingP. marginatusin many regions. We observed the occurrence ofA. papayaein Vietnam, studied the biological characteristics ofA. papayae, and investigated its parasitic activity onP. marginatus. The results showed thatA. papayaeoccurred more frequently thanAnagyrus loecki, another known parasitoid ofP. marginatus. The lifespan ofA. papayaewas approximately 16 days. In the absence of hosts, a 50% honey solution was an essential diet to increase the longevity of both female and male ofA. papayae. The second instar ofP. marginatuswas a suitable host stage for parasitism byA. papayae. FemaleA. papayaelaid approximately 60.8 eggs within 17 days, mostly during the first 6 to 7 days. These findings suggest thatA. papayaehas the potential to controlP. marginatus, and could inform the development of more effective pest management strategies for cassava crops in Vietnam and other regions affected by this pest.