Biology Reference
In-Depth Information
Nematus pavidus
Lepeletier (
997
)
Lesser willow sawfly
An abundant and often destructive pest of willow
(
Salix
); infestations also occur on alder (
Alnus
) and
poplar (
Populus
). Widely distributed in Europe.
Nematus salicis
(Linnaeus) (
998
)
Willow sawfly
A local pest of willow (
Salix
), especially crack
willow (
S. fragilis
) and white willow (
S. alba
). Widely
distributed in central and northern Europe.
DESCRIPTION
Adult:
6-7 mm long; head and thorax black; abdomen
mainly yellow (male usually with black crossbands);
antennae black; legs mainly yellowish; wings hyaline
with blackish veins, the pterostigma on each fore wing
brownish black.
Larva:
up to 20 mm long; head shiny
black; body green, with the first thoracic and last three
abdominal segments mainly orange; three black stripes
along the back, a single series of shiny black verrucae
along the sides and another series above the legs.
DESCRIPTION
Adult female:
8-10 mm long; head and thorax black;
abdomen and legs mainly yellow; wings hyaline with
black veins.
Larva:
up to 30 mm long; head shiny
black; body bluish green, with the thoracic and last three
abdominal segments brownish orange; numerous black
verrucae arranged in rows along the body, and
(predominantly on the green segments) five rows of
black marks along the back.
LIFE HISTORY
Adults occur most commonly from May to June and
from August to September, depositing eggs on the
underside of willow leaves. Young larvae feed
gregariously but as development progresses they
eventually disperse, older individuals usually occurring
singly or in pairs. When fully grown, the larvae enter the
soil to pupate in brownish-black, double-walled
cocoons.
LIFE HISTORY
Adult sawflies occur in two main generations, from
April to June and from August to September. Eggs are
deposited in dense groups on the underside of willow
leaves. Each female lays either fertilized or unfertilized
eggs. The former eventually give rise to females and the
latter develop parthenogenetically to produce males.
After eggs have hatched, the larvae feed along the edge
of the leaves, with the hind part of the body arched
upwards. The larvae occur at any time from May to
October, and are voracious feeders. Large numbers
typically occur together on the same leaf or branch.
Fully grown larvae eventually pupate in the soil in
tough, brownish cocoons.
DAMAGE
Larvae devour the tissue of fully expanded leaves but
cause far less damage than those of
Nematus pavidus
.
DAMAGE
Larvae rapidly reduce leaves to a mere network of
veins, heavy infestations affecting the appearance and
vigour of plants. Attacks are often very damaging in
osier beds.
997
998
997
Larva of lesser willow sawfly (
Nematus pavidus
).
998
Larva of willow sawfly (
Nematus salicis
).
Search WWH ::
Custom Search