Agriculture Reference
In-Depth Information
Opomyza florum
(F.)
Yellow cereal fly
This pest is associated with cereals and grasses,
and is often common. The larvae feed singly
within the centre shoots. Infested shoots
turn yellow and die; this typical 'dead-heart'
symptom appears in the early spring at about the
same time as damage caused by the larvae of
wheat bulb fly,
Delia coarctata
(p. 197). If an
infested shoot is removed from the leaf sheath,
a characteristic spiral mark may be seen running
down towards the base
(Plate 7e).
Early-sown
winter wheat (i.e. crops drilled before mid-
October) are most at risk but the larvae do
not move from tiller to tiller; at least in the
British Isles, this pest rarely causes significant
damage.
Fig. 254
Puparium of grass & cereal fly,
Geomyza
tripunctata
(x1O).
posterior spiracles
3-pored and borne on short
tubercles.
Puparium
4 mm long, dark reddish-
brown, elongate and obliquely truncated
anteriorly
(Plate 7d);
anterior spiracles
very
prominent
(Fig. 254).
BIOLOGY
Adults are active from mid-June onwards.
Oviposition, however, does not take place until
the autumn, when eggs are laid on the soil close
to host plants. The eggs do not begin to hatch
until late January or early February. Host plants
are then invaded, a single larva feeding within
the centre shoot and destroying the growing
point. Larvae are fully grown in 5-6 weeks, usu-
ally by the end of May, and pupation occurs
within the damaged shoots. Adults emerge about
3 weeks later. There is just one generation each
year.
Meromyza saltatrix
(L.)
Grass fly
Infestations of this minor pest occur on various
grasses, especially fodder grasses. The larvae
cause the central shoots of young plants to turn
yellow and die. Infestations also occur on wheat,
typically in crops following a grass ley. On older
plants, the larvae cause damage to the develop-
ing inflorescences. As a result, the flower heads
may not emerge properly from the enclosing leaf
sheath; the larvae have also been implicated in
the development of 'white' ears. Larvae are pale
green to pale bluish-green and up to 10 mm long,
with a minute pair of posterior spiracles. They
are, therefore, readily distinguished from other
ley pests such as gout fly,
Chloropspumilionis
(p.
194), yellow cereal fly,
Opomyza florum
(below)
and frit fly,
Oscinella frit
(p. 195). Larvae that
develop from eggs laid in summer feed within the
shoots of host plants and eventually pupate in
the spring. Although in the British Isles there is
probably just one generation annually, in conti-
nental Europe this species (unlike other mem-
bers of the genus) is bivoltine.
DESCRIPTION
Adult
2-4 mm long, yellow;
wings
clear, spotted
with black.
Egg
0.6 mm long, shiny white,
spindle-shaped, with several longitudinal ridges
and furrows.
Larva
up to 8 mm long, elongate
and creamish-white
(Plate
7f); no posterior pa-
pillae (cf. wheat bulb fly,
Delia coarctata,
p. 197);
mandibles
each with two large and three small
pointed projections;
anterior spiracles
promi-
nent, rosette-like but relatively small, usually
10-lobed (cf. frit fly,
Oscinella frit,
p. 195);
poste-
rior spiracles
3-pored and separated by a more or
less distinct U-shaped depression
(Fig. 255).
Puparium
4 mm long, yellowish-brown, abruptly
tapered anteriorly.
