Agriculture Reference
In-Depth Information
hatch about 2 weeks later. Larvae pass through
three instars and are fully fed in about 3 weeks.
They then drop to the ground to pupate a
few centimetres below the surface. New adults
emerge about 12 days later, usually in June and
July. These adults give rise to a further genera-
tion of larvae that produce adults in August and
September. In favourable situations, when the
rate of development is enhanced, there may be
three generations in a year.
crops (Brassicaceae), including watercress, but
nowadays attacks are generally uncommon.
Phaedon tumidulus
(Germar)
Celery leaf beetle
This beetle is associated with various umbel-
liferous plants and sometimes attacks cultivated
celery and parsley. The adults notch the edges
of expanded leaves and sometimes also feed on
the heart leaves. Damage, however, is of limited
importance. Adults (2.5-3.0mm long) are usu-
ally greenish-black but are sometimes bluish or
bronzy; they are distinguished from other species
of
Phaedon
by the very shiny, smooth thoracic
disc.
DESCRIPTION
Adult
2.5-3.5 mm long, bright metallic-blue, oval
and somewhat bulbous;
thoracic disc
distinctly
punctured;
elytra
each with eight fine longitu-
dinal lines of punctures
(Fig. 219). Egg
1mm
long, oval, yellow.
Larva
up to 6 mm long;
body
brownish-yellow to dark grey;
pinacula
black
and prominent;
head
black;
thoracic legs
black,
marked with yellow
(Plate 4e).
Phyllotreta cruciferae
(Goeze)
A turnip flea beetle
This flea beetle is a generally common pest
of Brassicaceae, including cabbage, cauliflower,
kale, radish, turnip and watercress, and orna-
mentals such as nasturtium, stock and wallflower.
Adults make small punctures in the cotyledons
and leaves. These pit-like blemishes often coa-
lesce, and damaged areas frequently develop into
holes as the plants grow. Attacks are usually most
serious in April and May, especially on seedlings
or recent transplants whose growth is retarded by
cold conditions or lack of moisture. Larvae bur-
row into the roots of host plants. They destroy the
outer tissue and often cause extensive damage to
the base of radish plants.
Phaedon armoraciae
(L.)
Mustard beetle
Adults are similar in appearance to those of
Phaedon cochleariae
(above) but are slightly
larger (3-4 mm long) and less brightly coloured.
They sometimes cause minor damage to brassica
BIOLOGY
Adults are active from early spring onwards,
when they feed on the leaves and cotyledons of
cabbage, radish and turnip, and certain other
members of the Brassicaceae. Eggs are depos-
ited in the soil, close to host plants, usually in
batches of 20-30; they hatch about 2 weeks later.
The larvae attack the roots and feed externally
for about 2 weeks. Individuals then pupate and
new adults emerge another 2 weeks later, usually
in late June, July or August. There is just one
generation each year.
Fig. 219 Watercress beetle,
Phaedon cochleariae
(x!8).
