Agriculture Reference
In-Depth Information
large blotch mines. Mined leaves appear
scorched and may eventually decay; this affects
the marketable quality of spinach plants. Growth
of plants, however, is rarely affected significantly
unless heavy infestations occur on young plants.
Crops are usually at greatest risk from first-
generation attacks; sugar beet crops are more
likely to suffer significant damage where crops
are drilled to a stand.
BIOLOGY
Adults appear in early spring and deposit their
eggs in small batches on the underside of host
leaves. The eggs hatch in about 5 days. The
larvae then burrow directly into the leaf tissue.
They feed gregariously for about 2 weeks and
form large, brown blotch mines, each of which
commences as a linear gallery. Fully grown lar-
vae enter the soil to pupate, and a second genera-
tion of adults emerges in July. In favourable
areas and seasons, a third generation of adults
appears from late August to early September.
Fig. 268 Puparium of manold fly,
Pegomya
hyoscyami
(xfO).
Phorbia securis
Tiensuu
Late-wheat shoot fly
This minor pest is associated mainly with spring
and winter wheat, but will also breed on grasses.
The larvae feed singly inside young plants, each
causing yellowing, wilting and death of the
centre shoot. Damage is rarely of significance
and usually most evident on backward crops. In
the British Isles, attacks are most often found
in eastern England.
DESCRIPTION
Adult
5-6 mm long;
thorax
mainly greyish-
brown;
abdomen
reddish-brown;
legs
yellow with
black tarsi.
Egg
0.8 mm long, broadly elongate,
white;
chorion
reticulate.
Larva
up to 8 mm
long, greenish-white to yellowish-white
(Plate
10b);
anterior spiracles
8-lobed, fan-like;
poste-
rior spiracles
relatively small, surrounded by nu-
merous prominent papillae (cf. spinach stem fly,
Delia echinata,
p. 198).
Puparium
6-7mm long,
dark reddish-brown, barrel-shaped;
posterior
spiracles
prominent
(Fig. 268).
BIOLOGY
Adults are active in March and April. Eggs are
then deposited singly beneath the outer edges of
the leaf sheaths of young wheat plants. The eggs
hatch a few days later. Each larva then burrows
downwards into a leaf sheath, to form a spiral
channel, before entering the central shoot. The
larvae continue to feed within the shoots for 2-4
weeks. They then enter the soil to pupate,
usually in late May or early June. Larvae
are present, therefore, later in the season than
those of the wheat bulb fly
(Delia coarctata,
p.
197). Individuals usually remain within the
puparium until the following spring, although
in favourable districts a second or at least a
partial second generation may occur on wild
grasses.
Pegomya rubivora
(Coquillett)
Loganberry cane fly
Infestations of this locally distributed pest occur
on blackberry, loganberry, raspberry and
Tayberry. Adult flies are active in the spring,
eggs then being deposited on newly emerging
canes. The larvae feed gregariously. They
burrow downwards to the base of the new canes,
which are often girdled; this causes the canes to
wilt and die. Pupation occurs in the soil, and
there is just one generation annually.
