The first signs of an infestation are small discoloured patches on the skin fruit skin, which develop from the "sting" of the female fly during ovipositon. Once hatched, fruit fly larvae able to tunnel deeply into the fruit flesh for feeding, spreading widely within infested fruit and making the whole fruit unpalatable. In certain fruit types, maggot infestation results in tissue breakdown and internal rotting associated with maggot infestation, but this varies with the type of fruit attacked. Affected young fruit tend to become distorted, callused and usually drop prematurely whereas affected mature fruits develop a water soaked appearance. The larval tunnels subsequently provide entry points for bacteria and fungi that cause the fruit to rot further. When only a few larvae develop, damage consists of an unsightly appearance and reduced marketability because of the egg laying punctures or tissue break down due to the decay .
|Steiner, L. F., 1957. Field Evaluation of Oriental Fruit Fly Insecticides in Hawaii. Journal of Economic Entomology, 50: 16-24.|
. Damage to crops has been estimated at between 50-80% in West Pakistan and even up to 100% in Malaysia
Bactrocera dorsalis was accidentally introduced in the United States between 1944 to 1945 and is now present and a major threat on all major Hawaiian islands 
“Bactrocera dorsalis (Hendel),“ by Ronald F.L. Mau, Jayma L. Matin & J. M. Diez. Crop Knowledge Master, Apr 2007, URL: http://www.extento.hawaii.edu/Kbase/Crop/Type/bactro_d.htm (accessed on 15 Nov 2016).
Figure 14: Pacific Islands distribution of Bactrocera dorsalis.Key: Black- Present, no further details; Blue- Widespread; Image credit: Copyright © 2016 Centre for Agriculture and Biosciences International (CABI)