Blueberry Maggot

Blueberry Maggot, Rhagoletis mendax (Curran), is the major pest of blueberries in many parts of the Northeast United state. The presence of infested fruit at harvest can result in the condemnation of whole fields of harvested fruit. Moreover, the control of the insect is complicated by its long emergence period, its migration tendencies, and the fact that it usually does not attack fruit until after harvest has begun.

The female fly is about 3/16 inch long. The abdomen is pointed and black with white cross bands. The wings are clear and marked with heavy black bands in the shape of an upside-down W. Several other species of fruit flies can be confused with blueberry maggot if they are not inspected carefully.

Adults are tiny, fragile flies approximately 2 to 3 mm long. Mature larvae are about 1 mm long and 0.3 mm wide, legless, and yellow to red in color. Gagné provides excellent details on larval and adult gall midge morphology.

Life Cycle: The blueberry maggot, or blueberry fruit fly, is the major insect pest of blueberries in Maine. The date of initial fly emergence is dependent upon soil temperature. Emergence will begin to take place in mid June if spring temperatures have been very hot, but not until mid July if spring temperatures have been unusually cool. Growers can estimate emergence if daily soil temperatures are measured.

Flies continue to emerge until early August. After emerging, the flies, which live for about 30 days, and spend one to two weeks feeding on dew, insect honeydew, and secretions on foliage. During this nourishment period, the adult females become sexually mature. It is believed that once flies are sexually mature they leave feeding sites and search for fruit. It is at this point that the flies colonize blueberry fields from the outside margins. Mating occurs on the fruit after which mated females seek out ripe blueberries in which to lay eggs. The females only lay a single egg in each fruit and each female can lay up to 100 eggs infesting up to 100 fruit in a period of 15 to 25 days.

The female fly punctures the skin of the blueberry with a long pointed structure called an ovipositor which can be withdrawn into the insect’s abdomen. Once the ovipositor is in the berry, a single white elongate egg is deposited. The fly then drags the ovipositor over the surface of the berry leaving behind a chemical called an ovipositing deterring pheromone. This chemical deters other flies from laying an egg in the same berry for a few days.

In 7 to 10 days the egg hatches and the larva begins feeding. The first maggots appear in berries about mid-July. The full grown larva is whitish in color, is about 7.75 mm long, round and pointed at one end and blunt at the other. As the larva feeds and grows, the berry begins to shrivel. After two or three weeks of feeding, the larva becomes full-grown, and the berry is almost completely destroyed. An infestation, if present, increases rapidly to a peak by approximately the second week of August. At this time, many of the larvae begin exiting the berries and dropping onto the soil.

The larvae burrow into the soil to a depth of 1 to 2 inches to pupate. The insect spends the fall, winter, and following spring in the soil in this resting stage encased in a tough, brown outer skin called a puparium from which the adult emerges in early summer. In the first year after pupation approximately 85 percent of the adult insects emerge. In the second year roughly 10 percent emerge. In the third and fourth years the remaining 5 percent of the flies emerge. This ensures the survival of the species. If a calamity should befall the population in any given year, some of the pupae would still be in the soil to emerge later.

Damage: Flower buds dry up and disintegrate within about two weeks after infestation. High levels of flower bud abortion may occur during winter and early spring. The severity of damage varies from year to year and tends to be worse after mild winters and in more southern locations. Vegetative meristems may also be infested and killed or damaged leaving only very short shoots with a few highly distorted leaves. After mid-May, little damage occurs in Florida even though new growth flushes continue throughout the summer. The severity of damage also varies from field to field. Young plantings in their 2nd or 3rd year often flower and fruit well, even while nearby fields of mature plantings have severe bud loss. This suggests a low vagility of the midges and a slow population increase to pest proportions.

Biological control: The listed two braconids : Opius melleus Gahan, Opius ferrugineus Gahan. These attack larvae; in New Jersey 10-40% of maggots may be destroyed. But apparently this is not an important factor since wild berries are always heavily infested even during years of high parasitism.

Cultural control: If possible use a harvesting machine to harvest all remaining fruit; this eliminates oviposition sites and should reduce future populations. Following this strategy for several years will gradually allow growers to eradicate spot infestations of the blueberry maggot.

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