Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 74

Kaltenbachiella pallida (Haliday) ( 147 )
This widespread species occurs during the summer on
various Lamiaceae, including mint ( Mentha ), marjoram
( Origanum vulgare ), thyme ( Thymus ) and woundwort
( Stachys ), where colonies of very small (0.9-1.3 mm
long), creamy-white aphids develop on the roots
amongst flocculent masses of white wax. Winged forms
appear in the late summer and early autumn, and then
migrate to elm ( Ulmus ) where, eventually, eggs are laid.
The eggs hatch in the following spring. Wingless aphids
then invade the unfurling foliage to initiate large, light
green leaf galls. Each gall is coated in short whitish
hairs, and develops at the base of the midrib as a
conspicuous swelling (15-20 mm across) which
protrudes both above and below the leaf blade. These
galls mature in the early summer. Winged aphids then
escape through a stellate opening and eventually
establish colonies on secondary (summer) herbaceous
hosts. Galls on primary (winter) hosts, although
disfiguring leaves of ornamental specimen trees, do not
affect plant growth.

DESCRIPTION
Apterous female [on spruce]: 1.5-2.0 mm long; white
to creamy white, with a brownish head, antennae and
legs; wax glands are prominent.

LIFE HISTORY
This species overwinters in the egg stage on aspen
( Populus tremula ). Grey poplar ( P. canescens ) also
serves as a primary (winter) host. The eggs hatch in
spring, and wingless aphids (fundatrices) then develop
on the smaller twigs. Their offspring feed on the young
shoots, causing a slight bending of the leaf stalks. In
June, winged forms appear and these migrate to the
roots of spruce trees. Ant-attended colonies then
develop on the roots, amongst flocculent masses of
white wax. In the early autumn, after one or two
wingless generations, winged aphids are produced.
These return to winter hosts where, following a sexual
phase, winter eggs are eventually laid. Colonies of
wingless aphids may persist throughout the year on the
roots of spruces.

Pachypappa tremulae (Linnaeus)
syn. Asiphum tremulae (Linnaeus);
Rhizomaria piceae Hartig
Spruce root aphid
A generally common and sometimes abundant pest of
spruce ( Picea ) trees, including Norway spruce ( P. abies )
grown for the Christmas market. Often present on the
roots of nursery stock, including container-grown
material, but also invading the superficial roots of older
trees. Present throughout central and northern Europe.

DAMAGE
Heavy infestations on the roots of spruces may cause
death of plants. Damage to winter hosts, however, is of
no importance.

Pemphiginus vesicarius (Passerini) ( 148-149 )
This species occurs mainly in the Apennines and parts
of Asia but is also present in the South Tyrol, from
northern Italy into Austria. The aphids inhabit
distinctive galls on black poplar ( Populus nigra ). The

147

148

147 Gall of Kaltenbachiella pallida on Ulmus . 148 Young gall of Pemphiginus vesicarius on Populus .