Agriculture Reference
In-Depth Information
and cauliflower. The larvae feed in galls on the
roots, and damage of greatest significance is
caused to young plants (seedlings or transplants)
during the autumn and early winter; plant
growth is checked severely if infestations are
heavy. Well-established crops are rarely harmed
but extensive galling on culinary swedes and tur-
nips may be troublesome.
BIOLOGY
Adults are active throughout the late spring and
summer. Eggs are deposited mainly in August
and September, each in a small hole excavated
by the egg-laying female in the roots of host
plants. The eggs hatch 1-2 weeks later. As the
larvae feed, they become enclosed in conspicu-
ous marble-like galls
(Plate 5e).
These galls oc-
cur just below the soil surface and, unlike those
caused on brassica roots by club-root disease, are
partly hollow
(Plate 5f).
Larvae complete their
development in the following spring, and emerge
from the galls in March or April to pupae in the
soil. Adults appear a few weeks later.
Fig. 231
Larva of cabbage stem weevil,
Ceutorhynchus pallidactylus
(x12).
swede and turnip. The larvae feed gregariously
within the petioles, stems and crowns, and heavy
infestations result in extensive hollowing and
rotting of the tissue
(Plate 5d),
stunting, malfor-
mation and, sometimes, death of plants. Surviv-
ing plants often develop without terminal shoots,
these being replaced by numerous weak lateral
shoots that flower later than normal and yield
poorly.
BIOLOGY
Adults occur in the autumn, eggs being laid
mainly from mid-October to mid-November.
The larvae feed inside host plants from October
onwards. They pass through three instars and
become fully grown in the following spring. Pu-
pation takes place in the soil a few centimetres
below the surface. New adults appear from
mid-May to early June. They aestivate during the
summer, in litter at the edges of woodlands
and in hedgerows, and reappear in September or
October.
DESCRIPTION
Adult
2-3 mm long, mainly black with a distinct
spur on each femur.
Egg
0.4 x 0.3 mm, oval
and translucent.
Larva
up to 6 mm long;
body
whitish;
head
brown.
Pupa
2-3 mm long, white.
Ceutorhynchus contractus
(Marsham)
Turnip stem weevil
This weevil is associated with
Sinapis arvensis
and various other wild related hosts. It is also
reported, occasionally, as a minor pest of culti-
vated Brassicaceae, especially turnip. The larvae
(which are creamish-white with a brown head)
feed within the petioles, each forming a short,
greenish gallery. Although some eggs are laid
in the autumn, most are deposited in the early
spring, soon after the adults emerge from hiber-
nation. Larvae complete their development
in May or early June, and the next generation of
adults emerges from June onwards. Adults are
2 mm long and mainly bluish-black or greenish-
black, with a coppery sheen; the rostrum is rela-
tively short and broad.
DESCRIPTION
Adult
2.2-3.5 mm long, mainly shiny black, with
a distinctive, pale yellowish mark on the 'shoul-
der' of each elytron;
legs
partly reddish.
Larva
up to 6mm long;
body
white;
head
brown.
Ceutorhynchus pleurostigma
(Marsham)
Turnip gall weevil
This weevil is a common but local pest of
brassica crops, especially culinary swede and
turnip, and late-sown or late-planted cabbage
