PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Cineraria leafminer
An example of a leafminer
Leafminers generally do not kill plants.
Scientific name
Chromatomyia syngenesiae (Order Diptera,
Agromyzidae). Minor pest in NSW, Victoria, SA.
Other leafminers are listed on page 67.
Host range
Mainly Asteraceae and related plants. eg
Ornamentals, eg cineraria, chrysanthemum,
gazania, gerbera, Helichrysum, also mist flower,
nasturtium.
Vegetables, eg lettuce.
Weeds, eg capeweed, prickly lettuce, sowthistle.
Description & damage
Adult flies are small inconspicuous grayishblack
flies 2-3 mm long. They may be seen
walking over the leaves of host plants during
winter and spring but they often go unnoticed.
They may fly slowly making short hopping flights
of about 1 meter at a time. Female flies feed by
repeatedly puncturing the undersurfaces of young
leaves with their ovipositors and sucking up the
sap which flows from the wound. These punctures
appear as bleached spots on the upper surface of
the leaf. On some varieties of chrysanthemum
these spots can be confused with early stages of
white rust. Larvae are creamy-white, legless and
4-5 mm long when fully fed. They have no head
and there is usually only one larva or maggot per
mine. Pupae are elongate, barrel-shaped, light
brown and about 2.5 mm long and can be easily
seen through the undersurface of the leaf at the end
of tunnels. A single leaf may contain several pupae.
Leaves. Foliage is spoilt. Maggots tunnel
between the upper and lower surfaces of leaves.
Initially the mines appear as pale, narrow, threadlike
lines but as the maggots grow, the mines
become wider and more obvious and may eventually
reach 1.5 mm in across. A trail of insect excreta
can often be seen in the mines when held up to the
light. Pupae are easily seen in the mines through
the leaf undersurface.
General. The appearance of foliage is spoilt
and in cinerarias and other species which become
heavily infested, plants may wilt and growth may
be severely retarded. If the leafmining of the
maggots destroys most of the leaves plants may
die. Very often, however, affected plants will still
produce a good crop of flowers.
Diagnostics.
Meandering leaf mines on leaves of susceptible
varieties.
Larvae and/or pupae can be seen through lower
leaf surfaces when held up to the light.
The only leafmining insect that attacks these
plants in Australia at present.
Lucid keys www.lucidcentral.org/
– Key to the World Genera of Eulophidae Parasitoids
(Hymenoptera) of Leafmining Agromyzidae (Diptera)
– Liriomyza Parasitoids in South East Asia
– Polyphagous Agromyzid Leafminers Identification
Key Tutorial is available at:
keys.lucidcentral.org/keys/v3/leafminers/tutorial.htm
Pest cycle
There is a complete metamorphosis (egg,
larva, pupa and adult) with several generations
each season. The life cycle from egg to adult takes
about 3-4 weeks. Female flies lay eggs singly
within the leaf tissues on the undersurfaces of
leaves and the puncture marks or ‘stings’ may be
seen as small scars on the leaf surface. Eggs hatch
in about 4-5 days and the larvae feed and tunnel
within the leaves between the upper and lower
epidermis for 15-18 days (Goodwin et al 2000).
When fully grown they pupate at the end of the
tunnel. Adult emerge 10 days later.
Fig. 45. Cineraria leafminer (Chromatomyia syngenesiae).
Damage caused by maggots. Left: Cineraria. PhotoNSW Dept of
Industry and Investment. Right: Marguerite daisy. PhotoCIT, Canberra.
(P.W.Unger)
Insects and allied pests - Diptera (flies) 73