Agriculture Reference
In-Depth Information
singly (cf.
Ceutorhynchus pallidactylus,
below) in
the young, elongating stems, close to a terminal
bud. The eggs hatch several weeks later and
larvae feed within the pith of the stems for up to
6 weeks. They then vacate the host plant and
enter the soil to pupate in an earthen cell. The
adult stage is reached 3-4 weeks later but the
weevils remain within their pupal cells through-
out the winter (cf.
C. pallidactylus,
below).
DESCRIPTION
Adult
3.2-4.0 mm long, greyish, with dis-
tinct blackish longitudinal furrows on the
elytra.
Larva
up to 7 mm long;
body
whitish at
first but finally yellowish;
head
brownish-black in
the first two instars, yellowish-brown in the third
(Plate 5b).
Fig. 230
Cabbage stem weevil,
Ceutorhynchus
pallidactylulus
(x20).
Ceutorhynchus pallidactylus
(Marsham)
Cabbage stem weevil
within the stems and petioles (cf.
Ceutorhynchus
napi,
above), and this causes slight blistering.
The eggs hatch 1-4 weeks later. Larvae feed
during late May and June, tunnelling within the
pith and often forming extensive galleries. When
fully grown, 3-6 weeks later, they vacate the
plants to pupate in the soil close to the surface.
New adults appear in July or early August,
and feed briefly on brassica plants before
overwintering in the shelter of field margins and
so on (cf. C.
napi,
above).
This widely distributed pest is common on
Brassicaceae, and often a problem on spring-
sown brassica crops. Larvae feed within the
stems and petioles, reducing plant vigour; heavy
infestations on spring-sown brassica seed crops
may significantly reduce yields. Larvae that
attack spring-sown Brussels sprout, cabbage and
cauliflower seedlings can also cause serious dam-
age, infested plants becoming stunted and de-
formed and the inner tissue spongy and brittle;
also, the stems of infested seedlings often break
when the seedlings are transplanted. Larval
infestations on winter rape often occur in the
lateral shoots but are of little or no significance.
When numerous, young adults emerging in sum-
mer can cause considerable damage to vegetable
brassicas, as they browse on the leaves and bite
into the underside of the petioles, mid-ribs and
other major veins, which then become scarred
and, sometimes, distorted.
DESCRIPTION
Adult
2.5-3.5 mm long, greyish-brown and
with a whitish patch of scales on the back, just
behind the thorax
(Fig. 230) (Plate 5c);
body
noticeably larger and more quadrate than that
of
Ceutorhynchus assimilis
(p. 154);
legs
reddish.
Egg
0.7 x 0.6 mm, oval, translucent,
smooth, shiny.
Larva
up to 6 mm long;
body
creamish-white and elongate
(Fig. 231);
head
pale yellowish-brown.
BIOLOGY
Adults emerge from hibernation from mid-April
onwards and then feed on various brassicaceous
hosts, including brassica seed crops and vegeta-
ble brassicas. Eggs are laid from mid-May on-
wards. They are placed in groups of five or six
Ceutorhynchus picitarsis
Gyllenhal
Rape winter stem weevil
This weevil is a local and usually uncommon pest
of winter brassica crops, including oilseed rape,
