Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 77

155

Stagona pini (Burmeister)
syn. S. crataegi Tullgren
Pine root aphid
Small colonies of this generally common and widely
distributed pest occur throughout the year on the roots
of pine ( Pinus ) trees. Infested parts of the root system
become covered in masses of bluish-white waxen
'wool', amongst which may be found the small
(1.5-2.0 mm long) greyish-white aphids; individuals
possess numerous wax glands but no siphunculi.
Attacks are most important on container-grown plants,
nursery stock and transplants. Severe infestations cause
yellowing of the needles, and wilting and death of
plants. Hawthorn ( Crataegus ) is the primary host, but
infestations on this plant are not harmful.

155 Young gall of elm leaf gall aphid ( Tetraneura ulmi )
on Ulmus .

Tetraneura ulmi (Linnaeus) ( 155-157 )
Elm leaf gall aphid
Widespread in north-western Europe, forming large,
conspicuous bean-like galls on the expanded leaves of
various kinds of elm ( Ulmus ). The galls develop from
the upper surface of the leaf blade, each attached by a
narrow stalk. The galls, which may exceed 15 mm in
height, are initially green but later turn cream and
finally brown. Pale yellowish or yellowish-white aphids
develop within the galls, amongst whitish masses of
flocculent wax. Eventually, in the summer, winged
forms are produced, and these finally escape through a
conspicuous basal aperture. These aphids migrate to
various grasses, where ant-attended colonies develop on
the roots. A return migration to the primary host takes
place in the autumn. The galls on elm leaves are very
conspicuous and often numerous; however, they do not
cause significant damage.

156

156 Mature galls of elm leaf gall aphid ( Tetraneura ulmi ) on
Ulmus .

157

157 Old galls of elm leaf gall aphid ( Tetraneura ulmi ) on Ulmus .