Agriculture Reference
In-Depth Information
hide beneath soil mulches, in soil crevices and so
on. The weevils will feed on various plants and
often ascend young trees to browse on the young
bark, buds and foliage. Eggs are laid in the
summer, and the larvae later feed on plant roots,
including those of various weeds. Fully grown
larvae pupate in the spring, and new adults
appear shortly afterwards. Some adults survive
for more than a year.
DESCRIPTION
Adult 6-7 mm long, strongly sculptured and
shiny black but coated in dull, greyish-brown
scales, giving an irregular, camouflage-like pat-
tern; body often coated with mud. Larva up to
8 mm long; body plump and creamish-white;
head brown.
Fig. 233 Larva of a clover leaf weevil, Hypera
postica (x15).
Otiorhynchus sulcatus (F.)
Vine weevil
dorsal line and a pair of pale subdorsal
bands. Egg 1.0 x 0.5 mm, oval, yellowish to
brownish. Larva up to 6 mm long; body
greenish with a white dorsal stripe (Fig. 233);
head brownish-black.
This insect is one of the most important pests of
horticultural crops, both outdoors and under
protection. The adults notch the edges of leaves,
and often cause extensive damage in strawberry
beds and in gardens and nurseries, especially on
favoured plants such as camellia and rhododen-
dron; the adults can also ring-bark young plants.
The larvae are usually of even greater signifi-
cance. They feed voraciously on the root system
of a wide variety of cultivated plants, destroying
the fine rootlets and larger roots; attacked plants
often wilt and die. The larvae also burrow into
crowns, corms and rhizomes. Larval damage is
often severe on herbaceous plants, soft-fruit
crops and containerized ornamentals.
Otiorhynchus singularis (L.)
Clay-coloured weevil
The clay-coloured weevil is an important horti-
cultural pest. Adults remove bark from trees and
shrubs; sometimes, they also ring-bark shoots or
stems and cause the death of plants. Attacks are
often of considerable importance on young trees
or new grafts. Adult weevils also attack leaves
and petioles, and kill the buds of plants. The
form and timing of damage vary from host to
host. On currant and raspberry, for example, the
petioles are partially severed; the leaves then,
characteristically, keel over. Larvae sometimes
cause damage to the roots of cultivated plants
but are relatively unimportant (cf. Otiorhynchus
sulcatus, below).
BIOLOGY
This species is univoltine and parthenogenetic,
adult females on outdoor crops usually appear-
ing in May and June. They feed at night and rest
during the daytime on host plants or hide
amongst debris on the ground. Eggs are laid in
the soil from late July onwards, each female de-
positing up to 800 or more in her lifetime. On
low-growing plants, such as strawberry, eggs are
sometimes placed in folds on the lower leaves.
BIOLOGY
Adults of this mainly parthenogenetic weevil are
active at night from April onwards; by day, they
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