Agriculture Reference
In-Depth Information
though attacks occur on cultivated teasel plants,
grown commercially to produce seed heads suit-
able for teasing fine cloth (such as that used as
billiard-table baize), they are not of significance
and generally pass unnoticed.
on a relatively long stalk;
posterior spiracles
7-
pored, each borne on a short stalk.
Puparium
reddish-brown, with distinct horn-like anterior
and posterior respiratory processes.
Family CHLOROPIDAE
Cetema elongata
(Meigen)
Phytomyza spondylii
Robineau-Desvoidy
This common species is associated with various
umbelliferous plants, including cultivated pars-
nip. The larvae are yellowish and form linear leaf
mines. They pupate on the ground after escaping
through a slit made in the lower surface of the
leaf. Adults (wing length: 2.1-2.4mm) are black-
ish, with the sides of the thorax pale; the legs are
black with just the knees of the forelegs yellow.
This species is associated with wild and culti-
vated grasses, including
Elytrigia repens
and
Poa
annua.
The central shoots of attacked plants turn
yellow but damage caused is of little or no eco-
nomic importance.
BIOLOGY
Adults appear over an extended period in May
and June. Eggs are then deposited singly on the
leaves of host plants. Larvae feed singly within
the central shoots from June or July onwards.
Development is slow, and individuals do not
pupate until the following spring, shortly before
the appearance of the adults.
Pseudonapomyza atra
(Meigen)
larva =
A cereal leaf miner
This widely distributed but local leaf miner is a
minor pest of barley; it is also associated with
oats, wheat and various grasses. The tips of in-
fested leaves become discoloured by the rela-
tively narrow, pale yellow leaf mines. Damage
sometimes attracts attention, but infestations are
rarely, if ever, of economic significance.
DESCRIPTION
Adult
3.0-3.5 mm long, mainly black to brownish-
black and distinctly shiny;
face and scutellum
yel-
low;
legs
mainly pale, with the anterior tarsi and
extreme tips of the hind tarsi black.
Larva
up to
6 mm long;
body
elongated, white with a greenish
tinge;
antennae
prominent;
anterior spiracles
with
five or six lobes;
posterior spiracles
borne on
broad, distinctly separated tubercles.
BIOLOGY
Adults appear in May, and those of a partial
second generation emerge in the summer. From
one to five eggs are deposited about 10 cm from
the tip of a leaf, each separately within the tissue
between two of the leaf veins. On hatching, each
larva forms a narrow but gradually widening gal-
lery, directed towards the leaf tip; the mine even-
tually turns abruptly towards the leaf base to
form an elongated, linear blotch within which
larval development is completed. Fully fed first-
generation larvae emerge in June and pupate in
the soil.
Chlorops pumilionis
(Bjerkander)
Gout fly
Although locally common, this pest is not of
major significance. Barley, rye, wheat and culti-
vated grasses such as meadow foxtail and timo-
thy are attacked but infestations do not occur on
oats; wild grasses, including
Elytrigia repens,
are
also hosts. Larvae of the overwintering genera-
tion cause a characteristic swelling of the basal
parts of infested shoots and tillers (the so-called
'gouty' symptom). Although sometimes locally
extensive on barley and wheat crops sown before
mid-October, effects on overall yield are insig-
nificant. Larvae of the summer generation cause
DESCRIPTION
Adult
minute (c. 2 mm long) and mainly black;
wings
1.3-1.7mm long.
Larva
up to 4mm long,
whitish-yellow and plump, with segmentally ar-
ranged rows of minute papillae;
anterior spiracles
prominent, each with about 11 lobes and borne
