Agriculture Reference
In-Depth Information
including mustard, rape, swede and turnip, infes-
tations on such crops are of little importance.
DESCRIPTION
Adult
40-44 mm wingspan;
forewings of male
mainly white, more or less suffused with black
both apically and basally, and venation dark-
ened;
forewings of female
more extensively
blackened, including two subcentral black spots;
hindwings
with underside mainly pale yellow,
the venation dusted with black scales.
Egg
1.3 mm long, pale green, spindle-shaped and
ribbed longitudinally.
Larva
up to 30 mm long;
body
mainly velvet-green with yellow markings
along either side (unlike the following species
there is no yellow dorsal line).
BIOLOGY
Adults of the spring generation occur in April
and May. Eggs are then laid in batches, mainly
on the underside of leaves. They hatch 1-2 weeks
later, depending on temperature. The larvae
feed gregariously and are fully grown in 4-6
weeks. They then pupate, usually suspending
themselves by a strand of silk to a nearby wall,
fence or other suitable support. Adults emerge
10-15 days later. Larvae of the summer genera-
tion occur from July onwards. In summer, large
numbers of adults may arrive from abroad
and these immigrants often boost resident
populations. The winter is passed in the pupal
stage.
Pieris rapae
(L.)
Small white butterfly
Larvae of this generally common pest often
cause damage to broccoli, Brussels sprout, cab-
bage, cauliflower, horseradish and other vegeta-
ble brassica crops. They devour the leaves and
also contaminate plants with frass. During the
daytime, the cryptically coloured larvae often lie
stretched out along the veins of the leaves and,
although often on the upper surface, are easily
overlooked.
DESCRIPTION
Adult
55-65 mm wingspan;
forewings of male
mainly white with the tip bordered in black
(tip pale yellow below);
forewings of female
more extensively blackened above, including
two subcentral black spots;
hindwings
mainly
white above, yellow below. Egg 1.5 mm long,
yellow, spindle-shaped and ribbed longitudi-
nally.
Larva
up to 40 mm long;
body
mainly
yellow to pale bluish-green, irregularly pat-
terned with black;
head
black anteriorly, blue
posteriorly
(Plate 14b). Pupa
20-24mm long,
dull greenish-grey to whitish, spotted with black.
BIOLOGY
Adults of the spring generation occur mainly in
March and April, and are very active in sunny
weather. They deposit their eggs singly on both
sides of the leaves of host plants. Larvae of the
first generation eventually pupate to produce a
second generation of adults in mid-summer.
Their larvae, which feed in late summer and
early autumn, are usually more numerous than
those of the earlier generation, especially if a
summer immigration of adults has occurred.
Pieris napi
(L.)
Green-veined white butterfly
Although larvae of this widely distributed spe-
cies often feed on cultivated brassica plants, they
are rarely numerous and occur mainly on wild
plants such as
Sisymbrium officinale.
This species
is, therefore, of little economic importance.
DESCRIPTION
Adult
40-45 mm wingspan;
forewings of male
mainly white with tip and base more or less
black, and a subcentral black spot (the latter
often absent in spring specimens);
forewings of
female
similar to those of male but with two
subcentral spots and a blackish dash on the hind
margin;
hindwings
mainly white above, with a
BIOLOGY
Adults occur in May and June, and in late July
and August. Eggs are laid singly on the leaves of
host plants and the larvae feed in summer and
autumn.
