PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Diagnostics.
Obtain local information on fruit fly species
which occur in your area. Posters of Fruit Flies
of Australia and the world may be purchased
from Scientific Advisory Services
www.saspl.com.au/
Plant Health Australia is developing a webbased
remote microscope system to improve
Australia’s fruit fly diagnostic capability.
Morphological differences between adults,
eg size, colour of abdomen. Experts may be
required to differentiate adults of different
species. Gene technology identifies strains.
Eggs and larvae of fruit flies look alike.
Experts are required to differentiate species.
On some hosts, fruit fly maggots can be
confused with those of ferment flies (Drosophila
spp.) which only attack ripe fruit. On other hosts,
eg tomato, fruit fly maggots may additionally be
confused with those of green tomato fly or
athergona (tomato fly).
Pest cycle
There is a complete metamorphosis (egg,
maggot, pupa and adult) with up to 5 or more
generations each year. Adults live for long
periods, mate at dusk and are often seen during the
day basking on the sunny side of trees feeding on
bacterial colonies which are more plentiful under
humid conditions. The adult female lays eggs
under the skin of the fruit. Hatching occurs in
2-3 days and the maggots burrow (tunnel) and
feed in the pulp (flesh) for 10 days or more.
When mature they leave the fruit and burrow into
the soil and pupate to form a smooth, light brown
pupa. Depending on the temperature the adult
fruit fly emerges from the pupa 2-8 weeks later,
mates within a week and females begin laying
eggs and the cycle starts again. The complete
cycle of the QFF from egg to adult takes about
5 weeks in hot weather while MFF may take as
few as 4 weeks. The life cycle of MFF in WA is
generally similar to that of the QFF.
‘Overwintering’
Fruit flies can be active all year round in warm
moist areas.
Fruit flies usually ‘overwinter’ as inactive
adults but are killed by cold winters, as are
pupae in the ground. It is likely that the pest is
introduced into these cooler regions each spring
and summer in infested fruit.
Spread
By movement of infested fruit and vegetables.
Airline passengers carrying a few pieces of
fruit are one of the main means for spread of fruit
flies from one country to another.
Adults are strong fliers and assisted by wind,
can travel many kilometers. Cyclonic winds may
carry fruit flies into northern Australia.
QFF extends southwards in Victoria every year.
Pest Free Areas (PFAs). Medfly and QFF do not
occur in these PFAs and are incapable of naturally
dispersing to these PFAs from infested areas, due
in part to the hostile conditions experienced in the
PFAs and surrounding lands. Introductions usually
occur through transport by humans which is
strictly controlled by legislation.
Conditions favouring
Warm moist conditions, especially after good
falls of summer rain. Hot dry weather reduces
numbers of emerging adults.
Fruit become susceptible to fruit fly some weeks
before harvest and maturity.
Infestations usually begins with earlier ripening
fruits, eg loquats. QFF mainly attacks summer
fruits, particularly later maturing varieties and
is more severe during mid to late summer.
Tree-ripened fruit. As the season progresses,
fruit fly populations, the attractiveness of fruit to
fruit fly and the risk of damage all increase.
Fig. 41. Queensland fruit fly
(Bactrocera tryoni). PhotoNSW Dept of
Industry and Investment (E.H.Zeck).
Enlarged x5
1. Eggs
2. Larva or maggot
3. Pupa
4. Adult fruit fly
Actual size
5. Apple showing punctures
been deposited
6. Peach showing decay and
tunnels of the maggots
7. Egg clusters beneath the skin
8. Pupa in the ground
Insects and allied pests - Diptera (flies) 69