INTRODUCTION.
The common name of small fruit fly comes from their small size and fondness for
fruits as egg laying and developmental sites. The name of vinegar fly comes from the fact
they develop in the briny or vinegarlike liquids at the top of imperfectly sealed canned
fruits and vegetables. Note that only flies of the family Tephritidae can properly be
called fruit flies. These are nuisance pests but may act as disease vectors. The best
known of these flies is D. melanogaster Meigen which has been used extensively in the
study of heredity. They are worldwide in distribution and are found throughout the United
States.
RECOGNITION.
(Drosophila spp.) Adults about 1/8" (3-4 mm) long, including the wings.
Color dull, tan to brownish yellow or brownish black; eyes usually bright red. Antenna
with feathery bristle (arista). Wing with coastal vein (thickened front margin) broken
twice, near end of humeral cross vein (short vein perpendicular to costa near wing base)
and near end of vein R, (lst vein behind costa). First hind tarsal segment long and
slender, much longer than 2nd segment. Drosophila melanogaster adults about 1/8" (3
mm) long, tan with abdomen blackish above and grayish below, and bright red eyes. Mature
D. metanogaster larvae are about 1/4-3/8" (7-8 mm) long, eyeless, legless, and
tapering towards head from large rounded rear segment, head represented by 2 dark hooks.
Color near white except mouth hooks black and tips of posterior terminal abdominal
spiracies (breathing pores) yellowish. Posterior spiracles at end of short stalks/fleshy
tubes which are in contact or joined at their bases. Other species may have posterior
spiracis stalks dark and/or have whorls of setae (hairs) at their ends, and/or have the
bottom side of abdomen with darkened cross bands (setulae).
SIMILAR GROUPS.
Small dung flies (Sphaeroceridae) with lst hind tarsal segment broad
and shorter than 2nd segment, wing with costal vein (thickened front margin) broken 3
times (additionally before humeral cross vein).
Humpbacked flies (Phoridae) with humpback appearance, wing with
strong/dark basal front veins (costal area) and 4-5 weaker (less distinct) unbranched
oblique veins, hind femora flattened.
Moth/drain/sewage flies (Psychodidae) have body and wing veins
densely covered with hairs.
Fungus gnats (Mycetophilidae) and darkwinged fungus gnats (Sciaridae)
are slender, long-legged, mosquitolike, with elongated coxae, wing costa (front margin)
unbroken, antenna lacks an arista/bristle.
Other small flies either lack antenna with a feathery bristle and/or
wing with a twice broken costal vein.
BIOLOGY.
Adult females lay their eggs (average about 500) near the surface of fermenting
fruits and vegetables or near the cover crack of imperfectly sealed containers of such
materials. The eggs hatch in about 30 hours. The larvae develop in the briny or
vinegarlike liquids of the fermenting materials where they feed near the surface and
primarily on the yeast, for about 5-6 days. Prior to pupation, the larvae crawl to drier
areas of the food or elsewhere. The brown, seedlike sheath containing the pupa (the
puparium) is formed from the last larval skin/exoskeleton. The newly emerged adults mate
in about 2 days. The life cycle (adult to adult) may be completed in 8-10 days at 85'F
(29'C). Their reproductive potential is enormous.
HABITS.
Small fruit flies are attracted primarily to fresh fruits and vegetables and
those fermenting because of yeast. Materials lose their attractiveness when they begin to
decay because of bacteria and fungi. Materials commonly infested include bananas, grapes,
peaches, pineapples, tomatoes, mustard pickles, potatoes, etc. and fermenting liquids such
as beer, cider, vinegar, and wine; some species are attracted to human and animal
excrement. The larvae develop primarily in liquids and near the surface but seek drier
areas for pupation. Newly emerged adults are attracted to lights. Because of their short
life cycle of 8-10 days, they can exploit many temporarily available developmental sites
such as sour mop and broom heads, fruit under a table or cabinet, fruit left out in a
bowl, etc. Dishwater and mop water full of food particles can accumulate on surfaces
and/or in crevices and ferment, providing ideal fly breeding conditions. Adults tend to
hover in small circles. Because of their small size, many species are able to penetrate
ordinary screens.
