Small Fruit Flies
Drosophilus spp., particularly Drosophila melanogaster Meigan, Drosophilidae, DIPTERA


DESCRIPTION

Adult - About 3 mm long, these flies have red eyes and yellowish bodies with dark bands. Though commonly referred to as fruit flies, they are more correctly termed small fruit flies, vinegar flies, or pomace flies.

Egg - The tiny white elongate eggs are only about 0.5 mm long and have 2 slender filaments near the head end. Though individual eggs are too small to be easily noticed, clusters of eggs often resemble white mold on the surface of produce.

Larva - The cream colored maggots develop through three instars. They are about 5 mm long when fully grown.

Pupa - Yellowish-white at first, the 3-mm-long pupae soon turn brown.


BIOLOGY

Distribution - Cosmopolitan in occurrence, small fruit flies are most likely to attain large populations around piles of overripe produce or in sweet potato storage houses.

Feeding Habits - Drosophila flies consume yeast and bacteria associated with the initial decay of plant materials. Sap flows, mushrooms, and overripe produce are all very attractive to these flies.

Damage - Unlike real fruit flies, Drosophila flies do not break the skin of sound fruits and vegetables. They breed only in cracked or decaying overripe produce. As a result, these flies and their maggots are most likely to develop large populations in cull piles, storage houses, or processing plants.

Life History - Small fruit flies sometimes overwinter as larvae or pupae in sheltered locations with an abundance of dry fermented plant material. However, they have been known to breed throughout the winter in sweet potato storage houses and in root cellars as far north as New Jersey. Egg laying, though, is much reduced at temperatures below 13 degrees C (55 F) or above 38 degrees C (90 F).

Eggs are deposited in cracked produce and incubate about 24 hours before hatching. When temperatures average 25 degrees C (77 F), larvae feed and develop to maturity in about 4 days. Pupation then occurs within the shrunken skin of the last larval instar. About 5 days later, adult flies emerge. Within 2 days, females begin ovipositing at the rate of about 25 eggs per day. This process continues for several weeks, each female eventually depositing an average of 500 eggs.

The length of a complete life cycle (adult to adult) varies with temperature. At 20 degrees C(68 F) about 15 days elapse, but at 29 degrees C (85 F), a life cycle is completed in only 8 days. Generations may be produced all year if temperature permits and fermenting produce is available.


CONTROL

Small fruit flies are subject to many natural enemies. Adults are parasitized by protozoa, fungi, nematodes, and mites and preyed upon by spiders and certain species of flies. Maggots are parasitized by certain wasps and preyed upon by staphylinid and nitidulid beetle larvae.

Infestations can be prevented by the destruction of piles of culled produce. Storage houses should be well screened and sealed to minimize fly entrance as much as possible. Still, chemical control in storage areas may be necessary. For up-to-date chemical recommendations, consult the current North Carolina Agricultural Chemicals Manual.

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