Agriculture Reference
In-Depth Information
the autumn, when winged forms are again pro-
duced. These aphids return to
Populus
where
egg-laying females (oviparae) eventually deposit
winter eggs. Populations on lettuce often persist
well into the winter, and a few aphids may sur-
vive in the soil to re-infest lettuces planted out in
the following year.
DESCRIPTION
Apterous female
1.6-2.5 mm long, elongate-oval,
yellowish-white, with a tuft of white wax
posteriorly and small, dark abdominal wax plates
clearly visible;
antennae
very short;
siphunculi
absent.
Fig. 195
Antennae of apterous aphids, family
Pemphigidae: (a) woolly aphid,
Eriosoma lanigerum;
(b) carrot root aphid,
Pemphigus phenax.
Pemphigus phenax
Borner & Blunck
Carrot root aphid
This species is a common but minor pest of car-
rot; it also forms disfiguring galls on
Populus
nigra
Ttalica'. Heavily infested carrots are weak-
ened and the quality (and, hence, value) of wax-
contaminated roots is reduced.
NOTE
Other species of
Eriosoma
are also associated
with fruit crops, e.g.
E. ulmi
(L.) (currant root aphid)
which, in summer, breeds on the roots of
Ribes,
and
E.
lanuginosum
(Hartig) (elm balloon-gall aphid) which,
also in summer, occurs on the roots and basal parts of
the trunks of pear trees. Both species overwinter on
Ulmus,
the primary host.
BIOLOGY
Overwintered eggs on
Populus
hatch in the
spring, and aphids move to the unfurling leaves
where they induce the formation of mid-rib galls.
Each gall becomes an elongate, somewhat wrin-
kled, reddish swelling (often tinged with yellow
laterally), packed with numerous wax-secreting
aphids. In summer, winged forms are produced
and these migrate to carrot plants where they
initiate dense colonies on the roots. The root-
feeding aphids produce copious amounts of white
waxen 'wool', which may carpet the ground when
heavily infested plants are lifted. There is a return
migration to
Populus
in the autumn, where win-
ter eggs are laid on the bark, but parthenogenetic
colonies may persist throughout the winter on
spring-lifted carrot crops; individuals can also
survive the winter in the soil.
Pemphigus bursarius
(L.)
Lettuce root aphid
This aphid is a widespread and often important
pest of lettuce; the leaves turn yellow and the
plants become stunted. Attacks can be very seri-
ous and, in dry weather, infested plants may be
killed; crops sown from April to June are most
likely to be attacked.
BIOLOGY
This species overwinters in the egg stage on
Populus nigra
Ttalica'. In the spring, wingless
females initiate characteristic pouch-like galls by
feeding on the petioles of young leaves. Small
colonies of aphids develop within these struc-
tures until, in the early summer, winged forms
are reared; they eventually escape through a
beak-like opening and migrate to wild and culti-
vated lettuce and to other Asteraceae, including
Sonchus.
Colonies of wingless aphids then de-
velop on the roots of these summer hosts until
DESCRIPTION
Aptera
(on carrot) 1.6-2.5 mm long, globular,
yellowish-white to pale yellow, coated with white
wax
(Plate 2f);
antennae
very short
(Fig. 195b);
siphunculi
absent.
