Agriculture Reference
In-Depth Information
nental Europe (e.g. in parts of northern France).
Prior to 1960, it was unknown in Europe. Al-
though attacked trees are often heavily infested,
effects on growth appear to be minimal.
BIOLOGY
This pest overwinters as first-instar nymphs,
which continue feeding but grow only slowly. In
the spring, following bud-burst, development is
rapid and the adult stage is reached in May. This
species is an unusual scale insect in that its nym-
phal and adult stages are surprisingly mobile;
adult females, for example, commonly migrate
from their feeding sites to the trunk and main
branches where they will eventually lay eggs.
Reproduction is usually parthenogenetic, al-
though males are by no means infrequent.
Fig. 197
Brown scale,
Parthenolecanium corni:
first-
instar nymph (xlOO).
DESCRIPTION
Adult female scale
7 mm long, brown, somewhat
darker centrally; rounded in outline but tapered
anteriorly, with a pronounced posterior
cleft.
Nymph
oval, flattened, brown with a dis-
tinct posterior cleft.
female then dies. Eggs, often up to a thousand in
each ovisac, hatch from June onwards. The
young nymphs then swarm over the foodplant
and eventually settle on the 1-year-old wood.
Here they begin feeding and, after passing
through three instars, reach the adult stage, usu-
ally in September or October. After mating, the
short-lived males die.
Family PSEUDOCOCCIDAE
(mealybugs)
Planococcus citri
(Risso)
Citrus mealybug
DESCRIPTION
Female scale
up to 6 mm long, dark brown, oval,
convex with a distinct posterior cleft.
Nymph
pale greyish-brown to brownish-orange, flat and
oval with a distinct posterior cleft.
Male scale
lmm long, whitish, boat-shaped.
Adult male
lmm long, mainly pinkish;
legs and antennae
brownish;
forewings
broad;
caudal filaments
very
long.
This mealybug is often abundant on glasshouse
ornamentals, especially under hot, humid condi-
tions. Vegetable crops such as tomato are also
attacked. The pinkish eggs are laid in large
batches and then surrounded by cottonwool-like
masses of wax; these conspicuous ovisacs often
attract attention. The adults are 3-4mm long and
pinkish, coated with whitish wax; the peripheral
and caudal waxen processes are characteristi-
cally short and stout (cf. glasshouse mealybug,
Pseudococcus affinis,
below).
Pulvinaria regalis
Canard
Horse-chestnut scale
Pseudococcus affinis
(Maskell)
Glasshouse mealybug
This American species is associated with various
ornamental trees and is nowadays a common
sight on roadside trees in towns and cities in
southern England; it is also now present in conti-
This mealybug is one of the most frequently en-
countered species on glasshouse crops. Heavy
