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|Many weevils are important agricultural pests and several species frequently cause damage|
to house and garden plants. Some of the main garden pests are shown below . . . . . .
Weevils belong to a very successful family of beetles (Curculionidae) with more than 50,000 species
worldwide. They vary in size from small seed weevils, less than 2 mm long, to the large pine weevils, 20-25 mm long.
Adult weevils are fairly easy to recognise since nearly all have a characteristic rostrum or snout projecting forward
from the head, with mandibles or jaws at the tip. Some species have a very long rostrum, which may exceed the length
of the rest of the body, but generally the rostrum is much shorter. In addition, most species have distinctly
elbowed antennae. The larval stages are relatively featureless white or yellowish grubs, usually legless, but with
a well-developed head and jaws. Adults and larvae of all species feed either on living or on dead plant tissues.
The larvae of many species feed enclosed inside the roots, stems or seeds of plants, and some of these types can
become serious pests of agricultural crops, garden plants and stored food products. The examples illustrated here
include the main species found in Europe that frequently attack garden ornamentals, fruit and vegetables.
Blossom Weevils (Anthonomus spp.)
The apple blossom weevil (Anthonomus pomorum) occurs throughout Europe and in parts
of North Africa and Asia, where it attacks the flower buds of apple and pear trees. Blossom fails to develop normally
in spring and flowers remain closed with dead petals attached. Careful examination of affected flowers may reveal weevil
larvae, pupae or adults inside.
Flower buds attacked
by blossom weevil
Adults of this weevil, with their fairly long, narrow rostrum or snout, are about 4 mm long, dark
reddish-brown in colour, usually with whitish transverse marks on each wing case. They hibernate during winter under
loose bark and in dead leaves or other accumulations of debris near apple and pear trees. In early spring the beetles
emerge from hibernation and fly or crawl onto apple trees and sometimes pear trees, where the females lay their eggs on
young flower buds. The larvae, which hatch after one to two weeks, feed inside the flower buds causing damage to the
petals and other flower parts, so that the flowers fail to open. The unopened petals of attacked buds eventually wilt
and turn brown, in a similar manner to buds damaged by frost. Usually a single larva develops in each affected flower
and, after feeding for a few weeks, it pupates inside the flower under the dead petals. Adult beetles appear in June
or July and feed on leaves for about a month before seeking hibernation sites.
Apple Blossom Weevil
(3-4 mm long)
Apple blossom weevils rarely cause appreciable crop losses since they tend to act as a natural thinning
agent, resulting in fewer but larger fruits. However, if the beetles are known to be locally important, blossom can be
protected by spraying trees with a suitable insecticide just before the flower buds open, in order to kill the female
weevils before they lay eggs.
Another weevil, called the strawberry blossom weevil (Anthonomus rubi), attacks the flower
buds of various plants belonging to the family Rosaceae, particularly raspberries, blackberries and strawberries. This species
resembles the apple blossom weevil, but the adult beetle is slightly smaller (2-3 mm long) and entirely black or dark brown
in colour (without paler marks on the wing cases).
Leaf Weevils (Phyllobius spp.)
These are dark brown to black, short-snouted weevils, densely covered with metallic gold or
greenish-bronze scales. They range in size from 4-9 and mm long, depending on species. The main pest species found
in Europe are the brown leaf weevil (Phyllobius oblongus), the silver-green leaf weevil
(Phyllobius argentatus) and the common leaf weevil (Phyllobius pyri), but a few other species
also occur in gardens. They feed on the leaves of apples and other fruits, and on the leaves of alder, birch, lime,
oak, poplars, flowering cherries, crab-apples and rhododendrons, eating small holes in the leaves and occasionally
damaging blossom. These weevils are usually seen on plants in May and June. They seldom cause severe damage and can
be controlled, if necessary, by spraying with a general purpose, contact-acting garden insecticide.
(5-6 mm long)
Pea and Bean Weevil (Sitona lineatus)
This is one of several different species of Sitona that feed on cultivated plants. The beetles
eat small, semi-circular pieces out of the edges of pea and bean leaves in spring and summer, producing a characteristic
scalloped or notched effect. Small, brown, short-snouted weevils, about 4 mm long, may be seen on affected plants, but
often drop off when disturbed. The pea and bean weevil is a common pest throughout Europe, North Africa and parts of Asia,
and it has been spread through commerce to North America and Australia.
The adult weevils overwinter in plant debris and coarse vegetation and move onto peas, beans and other
leguminous plants in early spring. Females lay eggs in the soil during warm weather and the larvae, which hatch about two
weeks later, feed for about a month on the nodules found on the roots of pea and bean plants, before pupating in the soil.
Adults appear in June or July and feed on various plants until the autumn, when they seek hibernation sites. Some virus
diseases of broad beans are transmitted by these and other weevils.
If necessary, young plants can be protected by dusting or spraying the leaves with a suitable
insecticide. Older plants are not greatly affected by this pest and rarely need treatment.
Pea & Bean Weevil
(4-5 mm long)
Vine & Root Weevils (Otiorhynchus spp.)
The vine weevil (Otiorhynchus sulcatus), shown at the top
of this page, is perhaps the most important species of Otiorhynchus because it attacks
many kinds of house and garden plants both indoors and outside, but several related species, such as the
clay-coloured or raspberry weevil (Otiorhynchus singularis) and the strawberry-root weevils
(Otiorhynchus ovatus and Otiorhynchus rugifrons), also attacked some garden plants outdoors. The
clay-coloured weevil is particularly associated with damage to apples, currants, gooseberries, raspberries, roses,
rhododendrons, polyanthus and clematis, whereas the strawberry-root weevils are mainly pests of strawberries. The biology
and treatment of the clay-coloured and strawberry-root weevils is much the same as for the vine weevil. All these species
are distributed worldwide.
Vine weevils are especially troublesome on container-grown plants in houses, conservatories and
glasshouses, but they also attacked plants growing outdoors in borders, rock gardens and similar situations. Potted
cyclamen, primulas and begonias are most susceptible to attack, but this pest also affects camellias, crassulas, ferns,
fuchsias, gloxinias, geraniums, grapevines, orchids, pansies, saxifrages, sanseverias, stawberries and many other plants.
Destruction of roots by a the larval stages checks growth and may cause sudden wilting and collapse of shoots and leaves.
Adult vine weevils are seldom seen since they are mainly nocturnal and hide during the day. Their presence is generally
indicated by irregular notches and holes eaten out of leaves and on some woody plants by the death of young shoots due
to ring-barking. Camellias and rhododendrons are very susceptible to this kind of damage.
The adult weevils (7-10 mm long ) are entirely dull black, usually with small patches of yellowish scales
on the wing cases, and the rostrum or snout is relatively short and broad. The legless, white larvae (up to 10 mm long) live
in the soil and look like miniature chafer grubs, but can be easily distinguished from these by the
lack of thoracic legs.
The biology of the vine weevil is unusual. Nearly all vine weevils are female and they can lay viable eggs
without being fertilised by a male. This ability to produce viable, unfertilised eggs is known as a parthenogenesis. Male vine
weevils have been found occasionally but are very rare. Each female weevil can lay several hundred eggs over a period of three
to four months during spring and summer and, although many of these eggs fail to hatch, a single female has the potential to
start a serious infestation. Eggs are laid in the soil or potting compost near suitable host plants. The larvae, which hatch
after about two weeks, feed on the underground parts of plants (i.e., roots, bulbs, corms or tubers) for several months
before pupating in the soil. Adults sometimes emerge in autumn, particularly on indoor plants, but generally not until the
following spring outdoors. There is one generation each year but, because of the staggered emergence of adults, there is
often some overlap of generations in late winter and early spring when eggs, larvae, pupae and adults may all be present at
the same time. Adult weevils are unable to fly but crawl into glasshouses through doors and ventilators or may be introduced
on newly acquired plants. They hide at soil level during the day, in leaf litter, cracks and crevices of loose brickwork or
woodwork and similar situations, and crawl up onto plants after dark.
Vine Weevil adult
(7-10 mm long)
Vine Weevil grub
(up to 10 mm long)
Vine weevil damage can be reduced by regular inspection of plants, good hygiene, and by the use of
chemical and/or biological control methods if available. In small gardens and greenhouses, frequent torchlight weevil
hunts after dark on warm spring and summer nights can help reduce adult populations and so limit egg-laying. During
re-potting of container-grown plants destroy any larvae, pupae or adults seen. Remove all accumulations of plant debris
that could provide shelter for the adult beetles. It is difficult to keep up to date with the range of chemical and
biological pesticides available to the general public for controlling household and garden pests. Seek advice from a
good pesticide stockist or garden centre for currently approved insecticide products.
REMEMBER TO USE INSECTICIDES SAFELY AND FOLLOW ALL THE INSTRUCTIONS ON THE PRODUCT LABEL
- See the Pesticide Safety Page for General Precautions on Insecticide Use -|
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