Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 386

Andricus curvator Hartig ( 1045 )
Oak bud collared-gall cynipid
Infestations of this species occur abundantly on oak
( Quercus ). Female wasps of the asexual generation
occur in February or March, initiating galls which
eventually develop on the major veins or stalks of the
young leaves. The galls cause considerable distortion of
the foliage, and often attract attention when present on
small trees. Each gall, which contains a single larva in
a large chamber, is light green to light brown and
measures 5-8 mm across. The larvae feed during April
and May, developing into male or female wasps which
emerge in June. After mating, females of the bisexual
generation deposit eggs between the scales of the leaf
buds, where small, inconspicuous 'collared galls' are
eventually formed. Such galls are commonly initiated in
buds already hosting the 'larch-cone gall' generation of
Andricus fecundator (see below). Development within
the galls commences in the summer and extends
throughout the following year, the complete lifecycle
thus occupying two years.

Andricus quercuscalicis (Burgsdorf)
( 1048-1050 )
Acorn cup gall cynipid
A widespread and common pest in mainland Europe
and, having appeared in southern England in the late
1950s, now well established in England and Wales; the
pest reached Scotland in 1995. Adult females appear in
the early spring, depositing eggs on the flower initials of
Turkish oak ( Quercus cerris ), a bisexual generation then
developing in galls on the catkins. Later, after the
production of males and females, eggs are deposited
in the acorn primordia of English oak ( Q. robur ).
Characteristic 'knopper' galls (usually one per infested
acorn) then develop from the acorn-cup tissue, each
containing a single, whitish larva. During the summer
the galled tissue expands into irregular, green, sticky
outgrowths; by the autumn these become brown and
woody; any acorns surviving within these infested cups
are also malformed. Mature galls fall from the tree in
October, still associated with the peduncle, the
occupants pupating before the onset of winter, each in
a small pupal cell within the shelter of the gall.
Infestations of this wasp are sometimes heavy and
totally prevent acorn production on some trees;
however, there appears to be no real effect on tree
growth.

Andricus fecundator (Hartig) ( 1046-1047 )
syn. A. foecundatrix (Hartig)
Larch-cone gall cynipid
This species is responsible for transforming the buds of
oak ( Quercus ) into artichoke-like larch-cone galls.
Each gall, which begins its development in June, is up
to 20 mm long at maturity, and contains a single larva.
Adult female wasps emerge from the galls in the
following spring but their emergence may be delayed
for up to three years. These wasps lay eggs in male
flower buds on oak, a bisexual generation then
developing in May to June inside hairy, catkin galls. The
resulting adults mate, females then depositing fertilized
eggs in leaf buds and thereby initiating the next round of
larch-cone galls. Attacks are most common on scrub-
oaks but also occur on nursery trees. The dead remains
of old larch-cone galls often persist on host plants for
several years.

Andricus quercustozae (Bosc)
A southern European, gall-forming pest of cork oak
( Quercus suber ), downy oak ( Q. pubescens ), English
oak ( Q. robur ), Hungarian oak ( Q. frainetto ), Pyrenean
oak ( Q. pyrenaica ) and sessile oak ( Q. petraea ), with a
single asexual generation. The females appear in early
spring and lay eggs singly in the buds of host plants.
Larvae then develop separately in unilocular, more or
less spherical, hard-walled, chestnut-brown galls, each
20-40 mm in diameter and with a central ring of hump-
like or thorn-like projections. Development from egg to
adult takes up to two years.