Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 105

brown and wrinkled. Male test: 2 mm long; elongate-
oval and brownish, with black markings and distinctly
paler ridges. Adult male: 1.5 mm long; delicate, pinkish
red, with brownish legs and antennae, a short caudal
spine and a pair of long caudal filaments; winged. Egg:
0.3 mm long; pale purplish red. First-instar nymph: 0.5
mm long; light purplish brown to orange-yellow, flat,
elongate-oval, with a distinct anal cleft.

DESCRIPTION
Adult female (scale): 7 mm long; brown; roundly
triangular, with a distinct posterior cleft. Male test:
3 mm long; similar to female scale but smaller,
narrower and lighter brown. Egg: minute, oval and
whitish. Nymph: oval, flat and brownish, with a distinct
posterior cleft.

LIFE HISTORY
Unlike most scale insects, this species displays
considerable mobility during its developmental stages.
Eggs hatch in June to July. First-instar nymphs then
migrate to the underside of leaves to begin feeding. In
September, when about 2 mm long, the nymphs move
onto the twigs where feeding continues throughout the
winter; growth, however, is slow. After bud-burst,
nymphal development become rapid and size differences
soon become obvious between the smaller males (if
present) and larger females, with dense colonies
developing on suitable hosts. Individuals become mature
by May. Before egg laying, the mature females migrate
from the twigs to the main branches and trunks. At this
time, female scales sometimes fall from host trees. They
may then be found on nearby low-growing plants or
other objects. Eggs, up to 2,000 per female, are
deposited beneath the maternal scales, mainly on the
branches and trunks of host plants but also on walls,
pavements and elsewhere. Although males occur,
females are capable of reproducing parthenogenetically
and usually form the bulk of populations.

LIFE HISTORY
Adults appear in September or October. The short-lived
males die after mating. Females, however, are longer-
lived and eventually overwinter. In early spring, the
surviving females begin to feed and grow, becoming
distinctly convex and darker in colour, while their backs
gradually harden to form a protective scale. From mid-
April or May onwards, when fully mature, each female
spins a white, cushion-like ovisac within which, over a
period of 2-3 weeks, 1,000 or more eggs are deposited.
The female then dies. The bulk of the egg mass forces
the scale away from the substratum, with the hind end
tilted upwards. The presence of the pest then becomes
particularly obvious as strands of waxen 'wool' from
beneath the scales are wafted about by the wind, often
covering many of the shoots and branches. Eggs hatch
from late May or early June onwards. The young, first-
instar nymphs, that typically appear in swarms, then
wander over the young shoots and leaves. Eventually,
the nymphs disperse to the one-year-old wood where
they settle down to continue their development. When
feeding, this pest excretes considerable quantities of
honeydew upon which sooty moulds may develop.
There are three nymphal instars, and the adult stage is
reached in the autumn. Although there is one generation
annually, details of the lifecycle vary according to
conditions. Also, populations may include both sexual
and asexual races.

DAMAGE
Although some hosts, notably limes and maples, are
colonized extensively, the scales appear to have little or
no effect on tree growth. Their presence on amenity or
ornamental trees, however, is unsightly and commonly
causes concern. Infested trees often bear whitish marks
on the bark long after the dead scales have fallen away.

DAMAGE
Heavy infestations, which occur on the leaves and
branches, and may extend down the main stems onto the
roots, severely weaken host plants. Waxen 'wool',
honeydew and sooty moulds also contaminate foliage
and other parts of host plants, and have a detrimental
effect on photosynthesis.

Pulvinaria vitis (Linnaeus) ( 223 )
Woolly vine scale
A highly polyphagous species, now known to include
Pulvinaria betulae and P. ribesiae , both of which have
been considered separate entities. Commonly infested
ornamentals include alder ( Alnus ), birch ( Betula ),
Cotoneaster , flowering currant ( Ribes sanguineum ),
hawthorn ( Crataegus ), ornamental vine ( Vitis vinifera )
and willow ( Salix ). Holarctic. Widely distributed in
Europe.

DESCRIPTION
Adult female (scale): 5-7 mm long; heart-shaped to
oval or circular, strongly convex and saddle-like; dark