Agriculture Reference
In-Depth Information
able conditions, there may be a partial second
generation. As many as three generations can
occur in heated glasshouses.
DESCRIPTION
Adult
35-40 mm wingspan;
forewings
purplish-
brown, with a yellowish stigma and a whitish,
irregular subterminal line;
hindwings
greyish.
Egg
hemispherical, ribbed and reticulated, whit-
ish to greenish.
Larva
up to 40 mm long;
body
green or brown, speckled finely with white and
with a pale subspiracular stripe;
spiracles
white,
ringed with black;
head
pale brown;
(Plate
15c). Pupa
16-19mm long, dark brown to black
and coarsely sculptured;
cremaster
with two T-
headed spines.
Fig. 322 Rosy rustic moth,
Hydraecia micacea
(x3).
Mamestra brassicae
(L.)
Cabbage moth
slender, dull pinkish to dark brown:
pinacula
blackish-brown;
head
yellowish-brown and
glossy;
prothoracic plate
yellowish-brown,
marked with brown anteriorly
(Plate 15b).
The cabbage moth is a generally common and
often important pest of vegetable crops, includ-
ing brassicas, lettuce, onion, pea and sweet corn.
Infestations often occur in glasshouses, espe-
cially on lettuce and sweet pepper and, less often,
other crops, including ornamentals. The young
larvae graze on the surface of leaves, leaving the
upper epidermis intact ('windowing' symptom)
(Plate 15d)
but older larvae bite right through
the lamina. The larvae also burrow into the heart
of cabbages and foul plants with their frass.
Lacanobia oleracea
(L.)
Tomato moth
This often common pest attacks various her-
baceous plants, but is of greatest importance
as a pest of glasshouse-grown vegetables, includ-
ing cucumber and tomato. Although young
larvae merely graze the leaves, older larvae
cause extensive defoliation. They also tunnel
into developing tomatoes, rendering the fruit
unmarketable.
BIOLOGY
Moths fly mainly in June and July. Eggs are laid
in large batches of 20-30 on the underside of
leaves of host plants and hatch within about 2
weeks. Larvae feed for about 5 weeks and then
pupate in the soil, each in a flimsy cocoon. Adults
usually emerge in the following spring but, under
favourable conditions (especially under glass), a
partial second generation emerges in the late
summer or early autumn.
BIOLOGY
Outdoors, adults occur mainly from late May to
early July. Eggs are laid in large batches on the
underside of leaves and they hatch 1-2 weeks
later. The larvae at first feed gregariously. On
attaining the second instar the larvae disperse
and feed singly. They usually pupate by Septem-
ber, each spinning a flimsy cocoon in the soil or
amongst debris on the ground. Adults usually
emerge in the following year but, under favour-
DESCRIPTION
Adult
38-45 mm wingspan;
forewings
greyish-
brown to blackish-brown, with often inconspicu-
