Melon Fly

Pests of Field Crops in Southern Africa

MELON FLY

(Diptera: Tephritidae)

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Text Box: The melon or pumpkin fly is an important pest of cucurbits throughout much of the world. There are a number of species of importance, the main ones being the two-spotted pumpkin fly, Dacus bivittatus, and the lesser cucurbit fly, Didacus ciliatus. These are true fruit flies, although in appearance quite unlike the common fruit flies that attack deciduous and subtropical fruits. They look more like smallish yellow-brown wasps, having a narrow “waist” but only a single pair of wings. The former species reaches about 10 mm in length, and the latter only about 7 mm. The larvae are typical white, legless and headless fly maggots, reaching about 10 mm in length. TOP

Text Box: A wide range of cucurbits is attacked, ranging from cucumber, melon, and various types of squash to pumpkin. The smaller species tends to attack smaller fruit. Occasionally other fruits such as wild fruits, granadillas or cotton bolls are attacked. TOP

Text Box: The damage is caused by the larvae, which tunnel in the fruit resulting in a rotting and pulpy mess. In some cucurbits, such as butternut squash, a large sunken hole with a hard surrounding mass of tissue is caused in the hard rind, and this may or may not have maggots inside, so that it appears that the actual egg-laying action is sometimes sufficient to cause considerable damage. Certainly egg-laying sites soon become sunken and darkened in colour. If very young fruit is attacked, it may abort, or outgrow the injury but remain permanently distorted. TOP

Text Box: Eggs are laid in the fruits in groups of up to about ten by means of the piercing ovipositor of the females. Within one or two days they hatch and the larvae begin feeding on the fruit. Within about two weeks the larvae leave the fruit to pupate shallowly in the soil beneath. Pupation takes one to two weeks in the summer, before the adults emerge. The cycle takes longer as winter approaches. The adults are quite long-lived, and tend to congregate during the winter in protected spots such as on the undersides of leaves or against the trunk of certain trees such as citrus, loquat, etc. They have also been observed feeding on the honeydew produced by scale insects and aphids. TOP

Text Box: It appears that crops planted early escape much of the attack by this pest. December and January plantings may be very severely infested if control measures are not applied. Once the larvae are within the fruit there is no way to control the infestation, so spray timing with this pest is critical. Infested fruits should be picked and destroyed to prevent the larvae from completing their life cycle, and it should be noted that after a crop is harvested, a considerable number of pupating flies may remain in the soil. One common way of attempting to control pumpkin fly is by the use of bait sprays aimed at the adults, made up of an insecticide such as malathion with sugar added to the mixture. The spray is applied either by using a sprayer, or the more simple method of spattering the crop with a brush dipped into a bucket of the mixture. The coarse droplets should attract the adults, in much the same way that they are attracted to feed on honeydew. However, the operation would need to be carried out regularly from soon after flowering begins (weekly and after rains) to keep on top of the infestation and prevent the flies from laying eggs in the fruit. Unfortunately, the spray/sugar mixture is also likely to be attractive to bees. Another commonly used insecticide for many years has been the organophosphate, fenthion. This insecticide has the property of being able to penetrate a short distance into the fruit and may therefore kill the eggs or newly hatched larvae. Obviously it is important when using this remedy that the fruits are as well-covered by the spray as possible, as any uncovered area will allow the eggs to develop unhindered. It is also important to adhere strictly to harvest intervals, particularly in crops such as cucumbers, which are eaten uncooked. TOP

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Dacus bivittatus. (Photo: N Wright, Florida Dept of Agric and Consumer services, Bugwood.org).

Sunken hole with hard rind caused by melon fly in water melon.