The adult melon fly is approximately the size of a house fly, about 6 to 8 mm long. The body is mostly orange-brown with a faint black T-shaped mark on the abdomen, and the clear wings have a large brown spot at the tip and a brown stripe at the hind edge in addition to lighter striping along the leading edge of the wing and near the base. The female has a short tube at the end of its body through which the pointed ovipositor can be extruded. The maggots (larvae) are creamy-white, legless and attain a length of 10 mm.
The damage to crops caused by melon flies result from 1) oviposition in fruit and soft tissues of vegetative parts of hosts 2) feeding by the larvae, and 3) decomposition of plant tissue by invading secondary microorganisms.
Larval feeding damage in fruits is the most damaging. Mature attacked fruits develop a water soaked appearance. Young fruits become distorted and usually drop. The larval tunnels provide entry points for bacteria and fungi that cause the fruit to rot. These maggots also attack young seedlings, succulent tap roots of watermelon, and stems and buds of host plants such as cucumber, squash and others.
Melon flies are considered occasional pests on papaya. In comparison, oriental fruit flies are considered as primary pests and Mediterranean fruit flies are rare pests in typical situations. Although the actual injury on papaya by fruit flies is relatively low, these flies are considered a major pest of papaya in terms of exporting from Hawaii to the US Mainland and Japan. It is therefore necessary to treat the papaya fruits with post-harvest quarantine treatments.
The economic importance of the melon fly cannot be evaluated entirely from the standpoint of the direct damage to the various crops affected. Quarantine laws aimed at preventing the entry and establishment of melon flies in areas where it does not occur often reduces the export potential of locally grown crops.