PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Crusader bug
An example of a shield bug
This native bug has a wide distribution over
Australia, but does not occur in Tasmania. It has
potential as a biological control agent for the giant
sensitive tree (Mimosa pigra) (Elliott et al 1998).
Scientific name
Mictis profana (Coreidae, Order Hemiptera).
Host range
Wide range of native and introduced plants.
Ornamentals, eg cassia, eucalypt, hibiscus, rose,
wattle, wisteria. Fruit, eg citrus, grape.
Description & damage
Plant damage is caused by the nymphs and adults
sucking sap from the young shoots.
Adult bugs are 20-30 mm long and dark
brown to black in colour. When wings are folded
there is a well-defined yellow, St Andrew's
Cross on its back, it is from this that the bug takes
its popular name. The undersurface of the body
and the long legs and antennae are brown, but in
some individuals the tips of the antennae are
orange. When disturbed adults fly readily and
exude an unpleasant smelling liquid. Nymphs
resemble the adults without the conspicuous
yellow cross. The 1 st stage nymphs are brown with
a reddish abdomen and look like large ants. Later
stage nymphs are brown and have two small
orange spots in the middle of the upper surfaces of
their abdomens. The developing wings (or
‘wingbuds’) are also marked with orange in the last
2 nymphal stages.
Shoots. Nymphs and adults suck sap from the
young growth including flowering shoots causing
them to wilt, turn brown and die.
General. May be an important pest of young
trees, eg Acacia spp. in the NT, A. ampliceps and
A. auriculiformis in plantations in Qld when almost
all trees and 95% of shoot tips can be attacked
causing dieback, loss of apical dominance and
‘bushing’ of trees.
DIAGNOSTICS.
Adults are identified by their creamy ‘cross’.
Nymphs move rapidly over the plant and
superficially look like rather large ants.
Unpleasant smell.
Wilted or dead tips of new growth which
may curl over. Crusader bugs causing the
damage may have long since departed to seek
a new food source.
Pest cycle
There is a gradual metamorphosis (egg, nymph
(5 stages), and adult) with 3-4 overlapping
generations each season. In spring, ‘overwintering’
females lay eggs in rows or groups on leaves, twigs
or fruit and sometimes debris on the soil. Eggs are
relatively large, elongated and brown, with a
rounded lid on top which is pushed off by the
young bug when emerging. Nymphs feed on the
foliage of host plants side by side with adults.
Adults can live for more than 4 weeks. A complete
life cycle takes about 8 weeks in summer.
‘Overwintering’
As adults in sheltered places emerging to attack
new growth in spring.
Spread
Adults can fly freely in warm weather.
Movement of infested plants (minor).
Conditions favoring
Late summer and autumn especially in cooler
regions. They are a sporadic pest, occurring one
season and not the next.
Fig. 102. Crusader bug (Mictis profana). Left: Nymph
sucking sap from tips of new wattle shoots which wither.
and die. Right: Nymphs and adults actual size (20-30
mm long). PhotoCIT, Canberra (P.W.Unger). PhotoNSW Dept of
Industry and Investment.
148 Insects and allied pests - Hemiptera (bugs, aphids, etc)