PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Fruit flies
Fruit flies are a major world-wide pest of
fruit. Control measures are compulsory under
legislation. In some areas, eg Tablelands of NSW,
fruit fly is often a sporadic pest and in some
seasons is not a problem. Some of the exotic fruit
fly present in countries to Australia’s north could
have devastating effects on many Australian crops
(page 66). There is a Fruit Fly Research Centre
(University of Sydney). Papaya fruit fly outbreaks
cost millions of dollars in lost trade, control,
treatment and eradication.
Scientific name
Fruit flies (Order Diptera, Family Tephritidae).
There are more than 100 species of fruit flies in
Australia about 16 species attack commercial fruit
(page 66). Queensland fruit fly (QFF) (Bactrocera
tryoni) is the pest species in eastern Australia and
Mediterranean fruit fly (Medfly) (Ceratitis
capitata) MFF is the pest species in WA. Many fruit
flies are native species and are not economic pests.
In the NT the major fruit flies are B. aquilonis and
B. jarvisi, both with wide host ranges.
Host range
QFF attacks a wider range of fruit than MFF.
Fruit and nuts, eg pome fruits (loquats early in
the season, apple, pear, quince), stone fruits
(apricot, peach, nectarine), avocado, banana, citrus
(especially grapefruit), fig, grape, most exotic fruit,
walnut, a variety of tropical and cultivated fruits.
Ornamental fruits, eg crabapple, peach,
japonica, fruiting berries, Clivia spp.
Vegetables, eg tomato, capsicum.
Native fruits, eg kangaroo apple, lilly-pilly,
native guava.
Description & damage
Adults are small colorful flies, wings are mostly
banded or spotted. The head is distinct, the
abdomen tapers to a point and the female has a
prominent ovipositor. Species differ slightly in size
and appearance. MFF are 4-5 mm long with a
yellow body marked with white, brown, blue and
black, mottled wings and pale green eyes. QFF are
about 7-8 mm long (a little larger than the common
housefly) and are reddish brown with yellow
markings on the thorax, wings are clear with a
narrow dark band along the front margins and a
transverse stripe near their base. MFF are not as
mobile as QFF. Maggots (larvae) are about
8-9 mm when fully grown (last stage larvae) and
are white to creamy-white. They have a pointed
head with a pair of small black hook-like jaws, no
legs, and a squarish rear end. Maggots are capable
of ‘skipping’ or ‘jumping’ up to 15 cm. In their
natural environment fruit flies have a positive
role as plant pollinators and as a source of food for
birds and vertebrates
Only fruit. is damaged.
Stings (egg laying punctures) vary depending on
the type of host attacked and are difficult to detect
in some fruits, eg mango, papaya. Stings are made
by the ovipositors of female fruit flies, small
punctures may be visible, sunken areas, sap may
be present and premature ripening adjacent to the
sting. Stings may also appear as small black marks
on the skin, which become discolored. They may
be surrounded by a ring of tissue that fails to
colour as the fruit ripens, rot may occur close to
the sting.
Maggots feed in fruit.
Fruit may rot due the introduction of decay
organisms after stinging and maggots feeding.
Fruit may fall following stinging and decay.
Fruit may be inedible or downgraded to
juice grade.
Location and degree of damage varies
with type of fruit, number of larvae in fruit and
the climatic conditions, eg
– Apple and pear. A discolored area may develop
around each sting. Burrowing by hatched maggots
in the fruit soon become noticeable. Decay can
readily be detected by hand.
– Loquat ‘stings’ are similar to those in apple.
Loquats are the main host of early infestations.
– Citrus are not good hosts. The citrus acid in fruit
pulp and oil in rind kill s many eggs and maggots.
The area around the sting may yellow, punctures
may ooze. Later, water-soaked areas around the
sting may develop green mould (Penicillium spp.).
– Stone fruit may appear intact and sound but
maggots are easily detected when fruit is opened.
Decay is associated with their activity especially
around the stone.
– QFF will lay eggs in all varieties of persimmon and
passionfruit but maggot development is rare.
– Home garden tomatoes may be heavily
infested in autumn. Commercial tomato crops are
seldom attacked except when grown in urban areas.
Postharvest losses include that from:
– Further development of maggots.
– Presence of fruit flies and their damage. Affected
fruit may be unsaleable or downgraded at market.
– Growers may be required to perform postharvest
treatments.
– Quarantine restrictions being imposed by domestic
or export markets. Affects export earnings.
Fig. 40. Queensland fruit fly (B. tryoni).
Upper: Fruit fly, actual size.
Lower: Maggots in a peach.
68 Insects and allied pests - Diptera (flies)