Agriculture Reference
In-Depth Information
The eggs hatch 1-2 weeks later. The first-instar
larvae are very mobile and immediately migrate
to the root system where they begin to feed.
Individuals pass through several instars and
become fully fed in the following spring. They
then pupate, each in a small earthen cell. The
adult stage is attained from mid-April onwards
but individuals remain
in situ
for a period before
finally emerging. Most adults die before the
onset of winter but some may survive for one or
more years. In heated glasshouses and other pro-
tected situations, the life-cycle is often acceler-
ated and young adults may emerge in the
autumn. Also, the period of egg laying is often
protracted and, as a result, all stages of the pest
may occur together.
Philopedon plagiatus
(Schaller)
Sand weevil
Adults of this widespread but locally distributed
weevil are most numerous in sandy districts.
They feed on the leaves of various plants and
sometimes cause minor damage to sugar beet
and other crops, biting out large semicircular
notches in the margins of cotyledons and leaves.
The weevils also sever the stems of young plants
at or about soil level. Attacks, which may also
occur on carrot and other crops, are of greatest
significance when plants are at the early seedling
stage. The larvae, which feed on plant roots, are
of no economic importance. In the British Isles,
attacks occur mainly in the Brecklands of Nor-
folk and Suffolk.
DESCRIPTION
Adult
7-10mm long, mainly black and shiny;
prothorax and elytra
deeply sculptured, the latter
often with several patches of yellowish
hairs.
Egg
0.7 mm in diameter, white and shiny
when newly laid but soon becoming brownish
if viable.
Larva
up to 10 mm long;
body
creamish to brownish-white;
head
reddish-brown
(Fig. 234). Pupa
7-10 mm long, white with dis-
tinct wing pads and other appendages.
NOTE Several other species of
Otiorhynchus,
e.g.
O. clavipes
(Bonsdorff),
O. ovatus
(L.) and
O.
rugosostriatus
(Goeze), are associated with fruit crops;
weevils from related genera (e.g.
Barypeith.es
and
Sciaphilus)
are also of pest status, e.g. on strawberry.
BIOLOGY
Adults overwinter in the soil. They emerge
in April and immediately begin to feed on host
plants. Eggs are deposited in the soil, usually
from late May to mid-June. Larvae feed from
June or July onwards, attacking the roots
of
Carduus, Cirsium,
grasses and various other
plants; development is slow and larvae become
fully grown late in the following year.
DESCRIPTION
Adult
4-8 mm long, oval, stout-bodied, with pro-
truding eyes and relatively thick legs;
body
black,
but thickly clothed in brownish to brownish-grey
scales;
elytra
with light and dark scales, which
give a longitudinally striped pattern
(Plate 6a),
and clothed with short upright hairs;
antennae
reddish.
Larva
up to 8 mm long;
body
white;
head
light brown.
Phyllobius pyri
(L.)
Common leaf weevil
This weevil is a generally abundant pest, espe-
cially in grassland areas. The adults feed on the
leaves of various trees, including fruit trees,
making irregular holes in the leaves and flower
petals. The larvae feed on the roots of various
plants but are most abundant on grasses. Larval
Fig. 234
Larva of vine weevil,
Otiorhynchus sulcatus
(x!5).
