PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Longtailed mealybug
Scientific name
Pseudococcus longispinus (Pseudococcidae, Order
Hemiptera). This is a common and key pest in
NSW, Victoria and WA. It is a minor pest in the
NT. Other mealybugs include:
Citrus mealybug (Planococcus citri)
Citrophilous mealybug (Pseudococcus calceolariae)
Root mealybug (Rhizoecus spp.)
Hibiscus mealybug (Maconellicoccus hirsutus)
Grass-crown mealybug (Antonina graminis)
Tuber mealybug (Pseudococcus affinis), the most
important root-feeding mealybug in Australia
See also page 144.
Closely related to scales but mealybugs remain
mobile throughout their lives. Mealybugs are a
major cause of plant damage in greenhouses.
Host range
Very wide host range. A serious pest of both
indoor and outdoor plants in warm, humid climates,
rarely attacks annuals but is an important pest of
perennial plants. They attack roots, stems and
leaves. Woody trees, shrubs and ferns are the most
important plants infested.
Ornamentals, eg trees and shrubs, herbaceous
plants, ferns, orchids, bulbs, African violets, cacti,
indoor plants, ornamental grasses, eg Papyrus,
a major greenhouse pest.
Fruit, eg citrus, custard apple, grapes.
Pastures, field crops, clovers.
Description & damage
Adult females are 3-5 mm long, slow moving,
oval, wingless, flattened with well developed legs.
Their bodies are covered with wax glands which
secrete a white mealy wax (hence the name
mealybug), which forms short hair-like filaments at
the sides of the body. The hind end bears a pair of
wax filaments which are usually longer than the
body and may be broken off. They have well
developed legs and antennae and when disturbed or
seeking fresh feeding sites, crawl slowly but freely.
The length of the side filaments are about ½ the
length of the body. Adult males are tiny, delicate
winged insects with long waxy tail filaments, but are
rarely seen. Nymphs. 1 st stage nymphs (crawlers)
are minute, pink and mobile. Later stage nymphs
resemble adult females. Males resemble females, but
later form cottony cocoons about 3 mm long within
which they develop. A colony can be almost
completely enveloped in a woolly mass.
Above-ground damage. Mealybugs feed on
stems and leaves by sucking sap and congregate in
sheltered parts, eg sheaths, leaf bases, leaf undersurfaces,
around buds, stems, lower parts of fronds,
crowns, flowers, where 2 pieces of fruit touch.
Infestations are often not noticed until numerous
and unsightly.
Sap feeding distorts and yellows foliage.
Unchecked infestations on soft-leaved plants,
eg African violet, cause them to wilt and die.
Economic damage on many plants is caused
by the large quantities of honeydew produced;
sooty mould develops on it, disfiguring leaves,
stems and fruit. Large infestations make plants
unsaleable.
Ants are attracted to honeydew. Coastal brown
ants (Pheidole megacephala) tend mealybugs
for honeydew and move them around and fend
off natural enemies.
Overseas mealybugs have been recorded as
transmitting virus diseases, eg citrus mealybugs
possibly vector banana streak virus (BSV).
Below-ground damage. Other species may
also feed on roots and this may not be noticed until
the plant is repotted, wilts or dies.
Diagnostics.
Check roots of wilted plants for mealybugs.
Indoor plants often have large numbers of some
species before their presence is noticed.
Do not confuse:
– Mealybug colonies with fungal growth.
– Mealybugs with the larvae of mealybug ladybirds
which feed on mealybugs. Ladybird larvae are
about 3 times as long as mealybugs. They have
long marginal filaments, are also covered with
white mealy material, but they are more active
and have biting mouthparts (Fig. 109 below).
Identification of species depends on:
– Length of anal filaments.
– Colour of body fluid exuded from dorsal glands.
– Presence of wax-free areas along the back.
– Expert help is usually needed.
Longtailed mealybug has tail filaments
longer than its body. When squashed, body fluid
is pale yellow and there is no wax-free area
along the back. Eggs laid beneath the body hatch
almost immediately. Do not confuse with:
– Citrophilous mealybug with tail filaments
about rd its body length, 4 dark longitudinal dorsal
stripes. Body fluid dark red, eggs laid in cottony sac.
– Citrus mealybug with tail filaments not more
than rd body length, median dorsal stripe. Body
fluid yellow-orange, eggs laid in cottony mass.
Longtailed mealybugs, 3-5 mm long.
Cluster of mealybugs.
Mealybug
ladybird larvae
8-15 mm long.
Fig. 109. Longtailed mealybug (Pseudococcus longispinus). Photos NSW Dept of Industry and Investment.
160 Insects and allied pests - Hemiptera (bugs, aphids, etc)
Cluster of mealybug ladybird
larvae.