PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Lerp insects, psyllids
Scientific name
Psyllids (Family Psyllidae, Order Hemiptera).
Many species in Australia are of little economic
significance but some may kill hosts.
Brown basket lerp (Cardiaspina fiscella)
Redgum sugar lerp (WA, NT, Qld) (Glycaspis blakei)
Bluegum psyllid (Ctenarytaina eucalypti)
Eucalypt shoot psyllid (Blastopsylla occidentalis)
Spottedgum psyllid (Eucalyptolyma maideni)
See also page 143
Host range
Lerp insects attack native trees, especially eucalypts.
Psyllids attack a wide range of native plants, eg
callistemon, eucalypts, hibiscus, grevillea, Christmas
bush, boronia, leucaena. Many psyllids are host
specific or restricted to one group of closely related
eucalypts, eg bluegum psyllid (Ctenarytaina eucalypti)
infests blue gum (E. globulus), shining gum and some
species with blue-grey foliage. Some eucalypt species
may be infested with many species of psyllids, eg
Sydney bluegum (E. saligna) may host 16 species.
Description & damage
Adult lerps and psyllids are small free living,
sap sucking insects (rather like aphids), with 2 pairs
of wings held roof-like over their head. They are not
strong fliers, but they can jump, hence their nickname
‘jumping plant lice’. Adult psyllids are up to
10 mm long.
Nymphs of lerp insects secrete a shell-like
covering called a lerp beneath which they shelter
and feed. The lerp has a characteristic shape and
colour for each species; it is about 1-5 mm across.
Nymphs may be seen either through the covering or
when it is removed. Unlike scales they remain fully
mobile through all stages. Some argue that the lerp
offers protection against predators and parasites
while others say that it protects it against
dehydration. The first sign of attack is the presence
of lerp coverings on leaves. Nymphs of psyllids
are free-living and do not form a lerp covering, but
secrete white waxy threads. They feed on leaves
and terminal shoots, causing distortion and discolouration.
Sometimes their feeding causes
exudation of sticky white sap which hides the insect.
Fig. 108. Lerp insects.
Left: Discoloured areas caused by lerp insects sucking
plant sap. Right: Leaves with lerp coverings. PhotosNSW
Dept of Industry and Investment.
Leaves. If attack is severe, masses of whitish
lerps give trees a silvery appearance. Discarded
lerp coverings fall from the tree. Purplish patches
develop on leaves due to the sucking of nymphs
and adults. The toxic saliva of some lerp insects
causes leaf tissue to break down and brown. Trees
look as if scorched by fire. If attack is severe,
infested leaves may fall prematurely. Lerp insects
produce honeydew which attracts ants and on
which sooty mould grows, making trees and
evergreen plants underneath appear black.
Cut foliage of bluegum is downgraded by
bluegum psyllid (Ctenarytaina eucalypti);
seedlings are injured in commercial nurseries.
Saplings of Dunn’s white gum (E. dunnii) in
plantations may be killed.
Single trees are unlikely to die from attack.
Psyllids tend to concentrate on the older less
vigorous lower foliage of a tree.
General. Populations ebb and flow. Local
outbreaks can slow tree growth and make trees
more susceptible to attack by other insects,
especially borers and termites. Lerps of some
species were used by aborigines as food.
Vigorously growing eucalypts can usually recover
from one infestation when psyllid populations
decline, but if infestations are sustained over
consecutive seasons, trees may die.
Diagnostics.
Silvery appearance of tree due to lerp coverings.
The differing shapes and patterns of lerps are
used to identify the species attacking a tree
(Fig. 108 below).
Do not confuse lerp covering with scale insects.
Do not confuse damaged left by lerps (after lerp
coverings have gone) with damage caused by
other sapsucking insects, fungal leaf spots or
environmental conditions.
Psyllids secret waxy threads and may hide in blobs
of plant sap, do not confuse with mealybugs.
Pest cycle
There is a gradual metamorphosis (egg,
5 nymphal stages and adult) with several
generations each season. Adult brown lace
lerps deposits their eggs on leaves. Eggs hatch
into tiny flattened pink crawlers which wander
over the leaf searching for stomata near a vein to
insert its stylets and start feeding on plant sap.
Once settled nymphs quickly secrete a lerp (made
of starch derived from the plant sap), which is
glued onto one side of the leaf. As nymphs grow
the lerps are enlarged from one edge. After the
winged adult has emerged and flown off, empty
lerps remain on the leaf for some time. The life
cycle may be completed in 1-2 months.
‘Overwintering’
The main lerp stage appears to be from autumn
through winter to spring. Adults appear in summer.
Spread
By adults flying within adjacent plantings but they
cannot fly far. Re-infestation is slow.
158 Insects and allied pests - Hemiptera (bugs, aphids, etc)