PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Leafblister sawflies
Scientific name
Phylacteophaga spp. (Order Hymenoptera). The
larvae of several moths and a beetle may also mine
in various species of eucalypts.
Beetle (Syrbis alycore)
Blackbutt leafminer (Acrocercops lacinella) (a moth)
Jarrah leafminer (Perthida glyphora) (a moth)
Host range
More than 30 species of eucalypts and occasionally
brush box. Host species include Eucalyptus
botryoides, E. grandis, E. saligna.
Description & damage
Adults are only 5 mm long and live for less than
a week and do not feed. Larvae are also small,
only about 5-6 mm in length, and are only seen if
the cuticle over the blistered leaf area is removed.
Blisters also contain excreta produced by the
larvae. Pupae. Oval-shaped cocoons may be seen
within the blistered area. An oval hole cut from
the center of the cocoon indicates that an adult
sawfly has emerged.
Leaves. Damage is caused by larvae mining
between the upper and lower leaf surfaces giving
the leaf a blistered appearance. At times almost
every leaf on young trees (< 5 m in height) may
be affected and the tree may have a scorched
appearance. Affected leaves fall, and trees < 5 m in
height may be completely defoliated. Larvae feed
on juvenile leaves and young adult leaves near the
ground, suggesting that leaf nutrition is more
important than leaf chemistry and may limit
populations once adult leaves start to form.
Leafmining damage. Heaviest damage
usually occurs to juvenile foliage within 6 m of the
ground. Older trees, therefore, are not so seriously
affected. Attack ceases on trees which have adult
foliage.
Diagnostics. Damage may be confused with:
Other leaf mining insects of eucalypts,
mostly moth larvae, but none construct a swollen
pupal chamber like that of the leaf blister sawfly.
The jarrah leafminer (Perthida glyphopa) is a
major pest of jarrah in WA.
Fungal leaf spots, eg Mycosphaerella, which
causes a leaf spot on juvenile foliage of blue
gums and allied species. This fungus is
prevalent in warm, moist environments and
causes pale, irregular lesions across both leaf
surfaces which may eventually crack and blister.
Check for larvae or cocoons in the blisters by
holding leaves up to light. Check for exit holes.
Pest cycle
There is a complete metamorphosis (egg,
larva, pupa and adult) with 4-8 generations each
year. The female sawfly cuts a slit in the leaf
usually near the mid-vein into which the egg is
laid. The leaf surface swells around the egg,
forming a small ‘egg gall’. The small larvae feed
between the leaf surfaces until the leaf appears
blistered. Larvae pupate in the leaf by constructing
their cocoons within the raised blister area and
a small winged sawfly later emerges from the
cocoon though a small hole in the leaf surface. Life
cycle takes about 6 weeks in summer to several
months in winter. Up to 150 eggs may be laid in a
single leaf by several females.
‘Overwintering’
As larvae in leaves in north central Victoria. Also
possibly in some areas as pupae in infested leaves.
Spread
Adults flying.
Movement of infested nursery or tube stock.
Conditions favouring
Activity ceases in cold weather but may continue
at a reduced rate during mild winters.
Large outbreaks can occur in young plantations.
Trees stressed by abnormal weather conditions,
eg drought, water logging; also soil deficiencies,
competition from weeds, browsing wallabies,
rabbits, livestock.
Fig. 94. Leafblister sawfly (Phylacteophaga spp.). Left: Leaves showing
leafmining damage by larvae. Larvae and excreta can be seen when leaves are
held up to light. Right: Larva and female adult sawfly (both 5-6 mm long)
Photo NSW Dept of Industry and Investment.
Insects and allied pests - Hymenoptera (ants, bees, sawflies, wasps) 127