sThe effects of five fruits (guava, mango, papaya, starfruit and tomato) on the larval survival, adult eclosion and size o/Bactrocera sp. (Malaysia B) were investigated. The percentage pupation and adult emergence from pupae were not affected by different hosts, except for guava which gave the lowest percentage of adult emergence. Papaya and mango yielded the largest adult (>2mm head width). Comparison of composition of fruits indicates that a high percentage of carbohydrate and high pH in fruits would produce larger adults. High larval density reduced the percentage of larval survival, adult emergence and adult size.