Agriculture Reference
In-Depth Information
November to mid-February - earlier than dam-
age caused by wheat bulb fly,
Delia coarctata
(p. 197) and yellow cereal fly,
Opomyza florum
(p. 183). On maize and sweet corn, young plants
usually survive attacks but emerging leaves or
shoots are twisted and ragged, and cobs will be of
poor quality.
Second-generation (summer) lar-
vae:
these occur mainly on the ears of oats and
cause the developing grains to become shrivelled
('fritted grain'); attacks launched before ear
emergence may result in 'blind' shoots; very
severe crop losses are reported.
BIOLOGY
Adults appear in the spring, usually from late
April onwards. Eggs are then laid at the base of
host plants, especially spring oats. They hatch 3^4
days later. Larvae feed within the shoots and take
about 2 weeks to develop. They then pupate
in
situ
and adults of the second generation appear
about 2 weeks later (usually in June and July).
Their eggs are usually deposited on the heads of
flowering oat plants, in the shelter of the glumes.
Eggs may also be deposited on the ears of wheat
plants. Second-generation larvae eventually pu-
pate within the grain and third-generation adults
appear in the autumn (usually from August to
October). Eggs of the autumn generation are laid
on young grasses (especially rye-grass) and on
volunteer cereals. The resulting larvae feed
throughout the autumn and into the winter, and
eventually pupate in the spring. Larvae transfer
readily from plant to plant, so that attacks may
appear on later-drilled crops, but they will not do
so at soil temperatures below 8°C.
Fig. 265
Frit fly,
Oscinella frit
(x25).
Oscinella vastator
(Curtis)
This species, along with various other close rela-
tives, is associated with grasses such as fescues,
rye-grasses and timothy. The larvae may, on oc-
casions, transfer from grasses to cereals (apart
from spring oats) and cause death of the central
shoots but economically important attacks are
rare. Adults of
Oscinella vastator
often require
separation from those of
O. frit
in water-trap
collections used to monitor frit fly numbers;
O.
vastator
is distinguishable by, for example, its
noticeably short, stubby, more brownish and
more strongly veined wings, the longer antennal
filament and usually more obviously banded
(black and yellow) legs.
DESCRIPTION
Adult
1.5 mm long, stout-bodied, shiny black
(Fig. 265);
legs
mainly, if not entirely, black
(cf.
Oscinella vastator,
below).
Egg
0.7 mm
long, broadly elongate, white, ridged longitu-
dinally.
Larva
up to 4 mm long, narrow-bodied,
creamish-white and translucent; no posterior
papillae
(Plate 9c)
(cf. wheat bulb fly,
Delia
coarctata,
p. 197);
anterior spiracles
fan-like and
inconspicuous, each with four to seven lobes (cf.
yellow cereal fly,
Opomyza florum,
p. 183);
pos-
terior spiracles
borne on small tubercles.
Family SCATHOPHAGIDAE
Nanna armillata
(Zetterstedt);
N. flavipes
(Fallen)
Timothy flies
Infestations of these generally common flies
occur on timothy grass. The larvae graze on the
