Agriculture Reference
In-Depth Information
of the pest's range to five or six in more southerly
regions, where pupae may also overwinter.
DESCRIPTION
Adult
16 mm wingspan;
forewings
mainly grey-
ish-brown, marked irregularly with brown and
white
(Plate lib). Egg
0.5-0.6 mm long,
creamish-white, suboval, flattened and with a
reticulated surface.
Larva
up to 11mm long;
body
greenish-white;
head
brown.
Pupa
6-
7 mm long, brown.
Fig. 274
Forewing of diamond-back moth,
Plutella
xylostella
(xlO).
tend to be two (occasionally three) main genera-
tions, the arrival of immigrants from continental
Europe (where there may be six or more genera-
tions annually) may result in overlapping broods
of larvae.
Plutella xylostella
(L.)
Diamond-back moth
This species is a notorious and cosmopolitan pest
of vegetable brassicas. Less-significant infesta-
tions also occur on brassica seed crops, including
oilseed rape. Larvae, when numerous, cause sig-
nificant leaf damage. Attacked leaves become
riddled with holes and the remaining tissue often
turns brown; infestations are of particular impor-
tance on cabbage and cauliflower, where the lar-
vae often invade the heart leaves. Seed heads of
swede and turnip are also liable to be destroyed.
In the British Isles, attacks tend to be sporadic
and are of greatest significance in hot, dry sum-
mers when large numbers of adults invade the
country from continental Europe.
DESCRIPTION
Adult
11-16 mm wingspan;
head and thorax
ivory-white;
forewings
light brown to dark
brown, with an irregular creamish to ivory-white
band on the hind margin
(Fig. 274)
(forming a
characteristic series of three diamond-shaped
marks when both forewings are held over the
back in repose);
hindwings
grey, with a long
fringe of hairs.
Egg
0.5 x 0.25 mm, elliptical and
pale lemon-yellow.
Larva
up to 12 mm long;
body
pale yellowish-green;
head
pale brown with
darker markings;
pinacula
large and pale;
body
hairs
black and prominent;
prothoracic plate
in-
conspicuous, with scattered blackish markings;
anal claspers
elongate and clearly visible from
above.
Pupa
6-8 mm long, at first pale green
but soon turning brown.
BIOLOGY
Pupae overwinter, and adults emerge in the fol-
lowing year, from May onwards. There are usu-
ally two main flight periods, from May to June
and from August to September. Adults are most
active at night but are readily disturbed during
the daytime. Females lay large numbers of eggs,
typically in groups of two or three. The eggs
hatch about 10 days later. At first, the larvae
mine within the leaf tissue but they then feed
externally on the underside of the expanded
leaves, sheltered by flimsy silken webs. Develop-
ment, which includes four larval instars, takes
approximately 3-4 weeks. Each larva then pu-
pates in an open, net-like cocoon (7-10 mm long)
spun on the foodplant. Adults emerge about 2
weeks later. Although in the British Isles there
Yponomeuta malinellus
Zeller
Apple small ermine moth
This species is a minor pest of apple. The larvae
feed gregariously, often coating the foodplant
with masses of characteristic webbing. Heavy in-
festations may lead to considerable defoliation
and significant fruit loss. Attacks occur most
frequently on unsprayed trees, such as those in
mature private gardens and old, neglected orch-
ards. This and other closely related species (the
latter associated with plants such as
Crataegus
monogyna, Euonymus europaeus, Primus avium,
