Melon Fly

The melon fly (Bactrocera cucurbitae) has long been a major pest of cucumbers in Hawaii. Melon fly damage occurs when adult female flies lay their eggs into fruit and sometimes into stems. An indentation often occurs at the site of oviposition and the fruit may or may not become curved. The eggs later hatch into maggots which live and feed within the fruit. Infested fruit frequently rot, either in the field or after harvest. Attacks are severe on young developing fruit, especially under high humidity conditions after summer rains. This pest has traditionally been controlled in problem areas with protein baits and an insecticide such as malathion applied to corn border rows. An advantage of this method is that insecticides for the melon fly are applied outside of the cucumber crop and does not upset the balance of aphid and leafminer natural enemies within the crop. The importance of sanitation to manage flies cannot be over-emphasized. Melon flies developing within the fruit from cucumbers and other fruiting vegetables such as melons, squashes, peppers, beans, and tomatoes may be major in-field reservoirs. Do not dispose of culled fruit with live melon fly larvae in areas close to the production field. Infested fruit left in the field will allow the melon fly to complete its life cycle and cause further damage. Promptly destroy old crops so that they do not serve as in-field reservoirs. Alternate weedy hosts of the melon fly include wild bittermelon or balsam pear (Momordica charantia L.), ivy gourd or scarlet-fruited gourd (Coccinea grandis (L.)), teasel or hedgehod gourd (Cucumis dipsaceus Ehrenberg ex. Spach), kupala (Sicyos pachycarpus)., castor bean (Ricinus communis), spiny amaranth (Amaranthus spinosus), rattlepod

   (Crotolaria incana), and wild euphorbia (Euphorbia geniculata). Wild bittermelon and ivy gourd are excellent melon fly hosts and are important reservoirs for this pest. These weeds are also reservoirs of important cucurbit virus diseases. Eight parasite and 6 predators are known to be natural enemies of melon flies in Hawaii but do not provide effective controls in commercial produce operations.

   Because of the prolific nature of this pest, organized area-wide controls in vegetable producing areas are more effective than single attack techniques followed by individual producers. The following factors should be considered in an integrated melon fly control program: 1) Evaluate population levels in and around the field-- Populations are likely in areas where weed hosts such as wild bittermelon and ivy gourd are present; 2) Honey-dew secretions in or around the field from aphids, scales or leafhopper feeding on foliage may attract melon fly populations into the field; 3) Corn borders are more effective as trap crops to attract melon flies in fields where alternate weed hosts are not prevalent around the field margins; 4) Periodically monitor melon fly populations through trapping.