Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 150

333

334

333 Larval mine of oak leaf-mining weevil ( Orchestes
quercus ) on Quercus .

334 Larva of oak leaf-mining weevil ( Orchestes quercus ).

channel, running from the midrib to the leaf margin; it
then expands into a small brown blotch. There are three
larval instars, fully fed larvae pupating within the
feeding gallery, each in a white, spherical cocoon. The
overwintered adults survive until the end of May or
early June, and the new generation of adults appears in
mid-June. These weevils continue feeding on the foliage
for several weeks before entering their overwintering
sites, often causing considerable leaf damage during
June and July. Most weevils enter hibernation in late
July or August, but some delay their departure until
mid-September. There is just one generation annually.

eventually moves into the leaf blade; mining then
transfers from the lower to the upper side of the leaf, the
gallery eventually terminating in an irregular brownish
blotch, clearly visible from above. The larvae are
greenish white and translucent, with a brown head.
When fully fed, usually in June or July, they pupate in
rounded transparent cocoons formed within the mine.
Young weevils emerge 1-2 weeks later. They feed on
the leaves and then hibernate, reappearing in the spring.
Adults are 2.5-3.5 mm long, and mainly reddish brown
to brownish black, with a yellow pubescence.

Orchestes rusci (Herbst) ( 335-336 )
syn. Rhynchaenus rusci (Herbst)
Birch leaf-mining weevil
Associated mainly with birch ( Betula ) and oak
( Quercus ), with adults present from March onwards.
Unlike those of the previous four species, the larval
gallery follows the leaf margin and then turns inwards
to terminate in a more or less circular blotch. When
fully grown, the larva cuts out a circular section from
above and below the mine, and then forms its cocoon on
the ground between these two epidermal discs. Leaves
formerly containing larvae are recognized by the
presence of a circular hole at the end of the deserted and
abruptly terminated mine. The adult weevils are
2.0-2.5 mm long and rather oval-bodied, with a black
pronotum and elytra, the latter with two bands of white
or yellow scale-like hairs; the antennae are red and the
legs black with brownish tarsi.

DAMAGE
Adults pepper the foliage with small holes and, if the
midrib is damaged, leaves may wilt. Larval galleries
cause distortion, and the tips of mined leaves turn
brown. Such damage is often extensive on woodland
trees and is also of considerable significance on
ornamental trees and hedges.

Orchestes quercus (Linnaeus) ( 333-334 )
syn. Rhynchaenus quercus (Linnaeus)
Oak leaf-mining weevil
This common species occurs on oak ( Quercus ) and is
noted occasionally on young ornamental trees. The
weevils are active from April or May onwards,
browsing on the surface of the leaves. Eggs are laid
singly, usually in the underside of the midrib. Following
egg hatch, the larva mines towards the leaf apex to form
an elongate gallery which passes along the midrib and