Biology Reference
In-Depth Information
983
LIFE HISTORY
Adults occur in the spring, depositing eggs in the leaves
of alder. The larvae then feed within distinctive
brownish blotch mines in the leaves. There are
commonly two or three mines on each infested leaf;
these commence their development separately close to
the leaf edge (cf.
Fenusa dohrnii
, pp. 371-2), but may
eventually coalesce to form one large chamber. When
feeding, the larvae remove all the tissue between the
upper and lower leaf surfaces, and eject frass through a
small slit made in the wall of the gallery; occupied
mines occur in June and July, and the larvae are clearly
visible if a mined leaf is held up to the light. Pupation
occurs within the mine in a brown, flat, disc-like
cocoon. A second generation of adults appears in the
summer, with a second and usually larger brood of
larvae feeding in the autumn.
983
Mines of
Heterarthrus aceris
in leaf of
Acer
.
984
DAMAGE
Infested leaves are extensively disfigured, spoiling the
appearance of specimen trees. Heavy attacks in the
autumn lead to premature leaf fall.
Heterarthrus aceris
(Kaltenbach) (
983
)
Locally common on field maple (
Acer campestre
) and
sycamore (
A. pseudoplatanus
). Adults (3.5-4.5 mm
long) are mainly black, with white legs; they occur in
May and June, eggs being laid singly in the tips of the
leaf lobes. The whitish larvae mine the leaves during the
summer, each forming a large, brown blotch. When
fully fed, each larva cuts out a circular section from the
upper cuticle of its feeding gallery, to which it attaches
a flat, disc-like cocoon. These habitations drop to the
ground before leaf fall, the occupants overwintering
and eventually pupating shortly before the emergence of
the adults. By flexing their bodies, individuals are
capable of propelling their cocoons; hence the
colloquial name 'jerking disc sawfly'. Although usually
of little significance as a pest, severe outbreaks of this
mainly parthenogenetic sawfly have occurred, with
extensive damage reported on ornamental maples
growing as amenity trees.
984
Larva of
Heterarthrus microcephalus
.
985
Heterarthrus microcephalus
(Klug) (
984-985
)
A generally common species, associated with various
kinds of willow (
Salix
) including, occasionally, nursery
and ornamental trees. The whitish larvae feed mainly
from July or August to September or October, forming
brown blotch mines on the leaves. Adults (3-5 mm
long) are black and shiny, with pale yellow legs; they
occur from May to July.
985
Mine of
Heterarthrus microcephalus
in leaf of
Salix
.
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