Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 388

Biorhiza pallida (Olivier) ( 1051 )
syn. B. aptera (Fabricius)
Oak-apple gall wasp
Galls caused by this widespread cynipid are often
common on scrub-oaks ( Quercus ). The galls develop in
spring, following egg laying in the base of axillary and
terminal buds by newly emerged wingless females.
Affected buds swell rapidly into smooth, slightly
irregular, whitish to brownish-yellow, soft, spongy galls
about 25-40 mm in diameter. These galls, which
contain several larvae, each within its own internal
chamber, become extensively tinged with pinkish red as
maturity is reached. Fully winged adults of both sexes
appear in June or July. Vacated galls eventually darken
and their remains often persist on trees long after the
emergence of the original occupants. After mating,
females of the summer generation enter the soil and
give rise to a unisexual brood which develops inside
root galls. Larvae of this generation complete their
development in about 16 months. The wingless females
then appear and ascend the trunks to initiate the next
crop of oak-apple galls.

Cynips longiventris Hartig ( 1053 )
syn. C. substituta Kinsey
Oak leaf striped-gall cynipid
Asexual galls formed by this locally common species
also occur on the underside of the leaves of oak
( Quercus ). They are irregular in shape, 7-8 mm across
and slightly flattened, with a hard, roughened wall; each
encloses a small larval cavity. The galls are whitish
yellow, marked with red, and often appear striped. They
develop during the summer months, reaching maturity
in October. The sexual generation develops in the spring
in the adventitious buds on old oak trees.

Cynips quercusfolii Linnaeus ( 1054-1055 )
syn. C. taschenbergi (Schlechtendal)
Oak leaf cherry-gall cynipid
A common and widely distributed cynipid, inducing the
formation of cherry-like galls on the underside of the
leaves of oak ( Quercus ), mainly English oak ( Q. robur )
and sessile oak ( Q. petraea ). The smooth, rounded galls,
each 15-20 mm in diameter, are at first green or
yellowish green but eventually become yellowish
brown, flushed with red. The galls arise from the major
veins but, in spite of their size, they do not cause
distortion, even when several occur on the same leaf.
On young trees, the galls are sometimes present in
considerable numbers. Each gall contains a single larva,
which develops within a small central cavity surrounded
by spongy tissue. The galls reach maturity by October,
but remain attached to the leaves after leaf fall. The
adult wasps, although fully formed, delay their escape
until mid-winter. These wasps initiate a bisexual
generation in dormant buds, adult males and females
eventually appearing in June. Fertilized eggs are then
deposited in leaf veins, initiating the next unisexual
cherry-gall generation.

Cynips divisa Hartig ( 1052 )
syn. C. verrucosa (Schlechtendal)
Oak bud red-gall cynipid
A locally distributed cynipid, forming smooth, whitish-
yellow to bright red, woody, thick-walled galls on the
underside of the leaves of oak ( Quercus ). Each gall
arises from a major vein, and encloses a small cavity
within which a small, whitish larva develops. The galls
represent the asexual generation and occur from July
onwards; adults appear in October. Although sometimes
numerous on young trees, the galls do not distort the
foliage and are often overlooked. A sexual generation
occurs in the spring, larvae developing in small
insignificant galls associated with the young leaves or
terminal buds.