Biology Reference
In-Depth Information
978
979
978
Larva of
Fenusa pusilla
.
979
Composite mine of
Fenusa pusilla
in leaf of
Betula
pendula
'Dalecarlica.
shoots. The larvae feed in kidney-shaped blotches,
infested leaves commonly containing several mines
which either remain separated throughout their
development or eventually unite into a common gallery
which may occupy the whole leaf. Fully grown larvae
pupate in the soil without forming cocoons. Occupied
mines occur from June to October, there being two or
more generations per year.
LIFE HISTORY
The larvae occur from July to October. They mine
within the leaves of alder, the galleries frequently
commencing close to the midrib (cf.
Heterarthrus
vagans
, p. 373); there are often several mines in the
same leaf. There are usually two generations annually,
adults appearing in May or June and in August; in
favourable conditions there may be a third generation.
Reproduction is parthenogenetic.
DAMAGE
Infested leaves are disfigured by the larval mines.
Heavily infested foliage turns completely brown and
drops prematurely, reducing the vigour of affected
shoots.
DAMAGE
The feeding galleries disfigure the foliage and, if
numerous, cause significant defoliation.
Fenusa pusilla
(Lepeletier) (
978-979
)
syn.
F. pumila
(Klug)
A locally common and sometimes important pest of
birch (
Betula
), especially downy birch (
B. pubescens
).
Holarctic, but probably introduced to North America.
Present throughout Europe.
Fenusa ulmi
Sundewall (
980
)
Elm leaf-mining sawfly
A generally common pest of elm (
Ulmus
). Holarctic but
probably introduced into North America. Widely
distributed in Europe.
DESCRIPTION
Adult:
2.5-3.5 mm long; mainly shiny black, the legs
with brownish tibiae and tarsi; antennae short.
Larva:
up to 8 mm long; flattened and tapered from front to
rear; head brownish; body white and translucent, with a
greenish tinge, finally becoming yellowish white; body
before final moult with a black dumbbell-shaped ventral
mark on the first thoracic segment and blackish or
brownish dots on the following two, three or four
segments; prolegs are lacking on the anal segment.
DESCRIPTION
Adult:
3-4 mm long; black and shiny, with short
antennae and slightly smoky wings.
Larva:
up to 10 mm
long; white to yellowish white, with a light brown head;
legs banded with brown; a ventral plate on the first and
a black dot on several of the following segments.
LIFE HISTORY
This insect is mainly parthenogenetic, adult females
occurring from late April to June and in August. The
larvae feed in blister mines formed in the leaves of elm
from June to July, and in September. The mines are
brown and tend to extend between the major veins
without crossing the midrib; there are usually several in
each infested leaf.
LIFE HISTORY
Adults occur mainly in May and June, and in July and
August. Eggs are laid in leaves of birch, usually towards
the midrib in the tissue between two major lateral veins,
the females tending to select young leaves on the new
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