Biology Reference
In-Depth Information
212
Eulecanium tiliae
(Linnaeus) (
212
)
syn.
E. capreae
(Linnaeus);
E. coryli
(Linnaeus)
Nut scale
A locally common pest of ornamental trees and shrubs,
including alder (
Alnus
),
Ceanothus, Cotoneaster
, elm
(
Ulmus
), firethorn (
Pyracantha
), hawthorn (
Crataegus
),
hornbeam (
Carpinus betulus
), horse chestnut (
Aesculus
hippocastanum
), lime (
Tilia
), oak (
Quercus
), rose
(
Rosa
), spindle (
Euonymus
) and sycamore (
Acer
pseudoplatanus
). Widely distributed in Europe; also
present in North America.
DESCRIPTION
Female scale:
5-6 mm across; dark chestnut-brown to
light brown or greyish brown, and strongly convex.
Male test:
2.0-2.5 mm long; greyish, elongate-oval.
Adult male:
reddish crimson, with a relatively short
caudal spine and a pair of long caudal filaments.
Egg:
pale yellowish white.
Nymph:
212
Colony of nut scale (
Eulecanium tiliae
).
213
pinkish to orange-
yellow.
LIFE HISTORY
Adult males emerge in late April and early May, and
eggs are deposited by fertilized females about a
month later. The eggs hatch towards the end of the
summer. First-instar nymphs then wander over host
plants before settling down. Young overwintering male
and female scales are similar in appearance, and about
1.5-2.0 mm long. However, the more elongate
appearance of the former becomes obvious in the spring
as development recommences. This species also breeds
parthenogenetically.
213
Wisteria scale (
Eulecanium excrescens
).
DAMAGE
Heavy infestations retard growth, and host plants may
be killed. Minor attacks are of little or no significance.
LIFE HISTORY
In England, the pest has just one generation annually. It
overwinters in an early nymphal stage, the nymphs
eventually reaching maturity in late April or early May.
The exceptionally large female scales deposit masses of
eggs beneath their bodies, and then die. Following egg
hatch, first-instar nymphs emerge
en masse
from
beneath the maternal scales and swarm over the
foodplant. Initially, these highly mobile nymphs feed on
the foliage. Later, they move to the bark of shoots and
stems, where they become sedentary and, eventually,
overwinter.
Eulecanium excrescens
(Ferris) (
213
)
Wisteria scale
In Asia, this extremely polyphagous species occurs on
rosaceous fruit trees and a wide range of ornamental trees
and shrubs. It was unknown in Europe until infestations
were found in 2001 in Central London, England, on
Wisteria
and certain other ornamentals. The pest also
occurs as an introduced species on
Wisteria
in the USA.
DESCRIPTION
Adult female (scale):
13 mm long; globular, strongly
concave, with an irregular surface; dark brown to
blackish, often dusted with a greyish waxen bloom.
Egg:
0.5 mm long; pinkish orange.
First-instar
nymph:
orange (older nymphs brown, with distinct
waxen patches).
DAMAGE
Infested hosts are weakened and soiled by honeydew,
upon which sooty moulds develop. Severe infestations
may result in the death of host plants.
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