Gardening on Maui: How to manage fruit flies

Fruit flies are serious pests in Hawaii, feeding on hundreds of host plant species. They can occur from sea level to above 7,000 feet elevation. There are four species of fruit fly found in Hawaii: the melon fly, the oriental fruit fly, the Mediterranean fruit fly and the solanaceous fruit fly. The melon fly and the oriental fruit fly are the most commonly found fruit flies on Maui.

Fruit flies lay their eggs in the flesh of fruits and vegetables. The eggs hatch in one to two days, and the larvae tunnel through the fruit over the course of 5 to 15 days, feeding on the flesh. It’s during this time that you’ll see the characteristic small white maggots.

After the larvae emerge, they burrow into the soil to pupate. Adult flies emerge in approximately one to two days. Mating can occur within one to five weeks after this and the cycle begins again.

The oriental fruit fly has clear wings and can be found at most elevations, sea level to 4,000 feet. They are active after sunrise to mid-day. In the heat of the day, the flies stay inside the foliage. Major hosts for oriental fruit fly include most fruits, including breadfruit, citrus, guava, mango, banana and papaya.

The melon fly is common at sea level to 1,500-feet elevations and can be identified by a black spot at the wing tips and a black streak on the wing. Melon flies also are active sunrise to mid-day, but in the heat of the day, they hide within the foliage of roosting hosts such as corn or hibisicus. Major hosts include bitter melon, cucumber, eggplant, melon, pepper, pumpkin, squash, tomato and zucchini.

Management of fruit flies must include field sanitation. Removing fallen fruit prevents the flies from burrowing and pupating in the soil, thus breaking the cycle. Homemade traps containing specific lures can be used to determine which type of fly you have in your garden. Oriental fruit flies are attracted to methyl eugenol lures, while melon flies are attracted to cue-lures. The traps offer some control, but they only attract male flies. Protein baits, such as GF-120, are needed to control the female flies. The proper identification of the fly is important because the bait should be applied to the roosting plants in the case of the melon fly and in and around the host plants of the oriental fruit fly.

Here are the instructions for a simple fruit fly trap assembly with a 2-liter plastic soda bottle:

* Cut bottle crosswise, just above the top of the label, so that both sides of the bottle have the same diameter. The bottle cap is not needed.

* Use latex gloves or a small plastic bag to keep your hands from coming in contact with the lure. Protect the lure by covering it with a meshlike cloth or an old stocking. Attach the fruit fly lure plug to one end of a 12-inch sturdy but flexible 16-gauge galvanized utility wire.

* Drill a 1/8- to- 1/16-inch hole through the center of the bottom piece of the bottle. Insert the wire through the hole so that the lure hangs on the inside of the cut bottle. The wire sticking out of the bottle will be used for hanging the trap.

* With the bottom held upside down, insert the top of the bottle into it, with the bottle mouth facing upward. Be sure that the lure does not cover the bottle opening.

* Hang the trap in semi-shade out of reach of children and animals.

For more information, contact the University of Hawaii Cooperative Extension Service office at 244-3242.

* Lorraine Brooks is an urban horticulture extension agent and the Maui Master Gardener coordinator with the University of Hawaii’s Cooperative Extension Service, part of the College of Tropical Agriculture and Human Resources. Her email is Gardening On Maui will run when there is a fifth Sunday of the month.