Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 75

galls develop at the base of the young shoots as
irregular, brownish growth several centimetres across.
Greyish-bodied nymphs develop within the galls
amongst flocculent masses of whitish wax. Winged
adults eventually escape through small openings (which
eventually appear in the wall) and disperse to unknown
summer hosts. Vacated galls persist on host trees as
distinctive, shrunken, black, woody structures. They are
sometimes found on young amenity trees but damage
caused by the aphids is of little or no importance.

eventually escape through a beak-like opening. These
migrants then invade summer hosts, including Lactuca ,
sow-thistle ( Sonchus ) and various other Asteraceae.
Colonies of wingless aphids then build up on the roots
until the autumn, when winged forms return to poplar.
Following a sexual phase, winter eggs are eventually
laid.

DAMAGE
Poplar: autumn populations distort and discolour the
foliage but such damage is not of significance; galling
in spring is also unimportant.

Pemphigus bursarius (Linnaeus) ( 150-151 )
Lettuce root aphid
A generally common gall-forming aphid on Lombardy
poplar ( Populus nigra 'Italica') but most important as a
pest of cultivated chicory and lettuce. Present
throughout Europe; also found in North America and
Australia.

DESCRIPTION
Apterous female: 1.6-2.5 mm long; elongate-oval,
yellowish white, with a tuft of white wax posteriorly;
small, dark abdominal wax plates clearly visible;
siphunculi reduced to mere rings. Alate: 1.7-2.2 mm
long; abdomen brownish orange.

149

LIFE HISTORY
This species overwinters in the egg stage on Lombardy
poplar. In the spring, wingless females initiate
characteristic pouch-like galls by feeding on the leaf
stalks. Small colonies of aphids develop within these
structures until, in the early summer, winged forms

149 Old gall of Pemphiginus vesicarius on Populus .

150

151

150 Colony of lettuce root aphid ( Pemphigus bursarius )
in gall on Populus .

151 Mature gall of lettuce root aphid ( Pemphigus bursarius )
on Populus .