Agriculture Reference
In-Depth Information
Fig. 266
Tubercles on the anal segment of
Delia
larvae: (a) onion fly,
D. antiqua;
(b) wheat bulb fly,
D. coarctata;
(c) bean seed fly,
D. platura;
(d) cabbage root fly,
D. radicum.
Fig. 267 Puparium of wheat bulb fly,
Delia coarctata
(xlO).
spring barley or spring wheat (usually crops
sown before early March), but not on oats;
Elytrigia repens
is a wild host. Larvae cause the
yellowing and death of central shoots ('dead-
heart' symptom). Individual larvae typically
move from one shoot to another, and overall
effects on yield may be considerable, especially
on untillered crops. On heavy land, attacks are
usually most severe on crops which follow
fallows or bastard fallows (leys ploughed-up in
July); on lighter-land sites, the risk of attack is
greatest when host crops follow pea, potato and
root crops such as sugar beet. In the British
Isles, infestations occur mainly in the midland
and eastern counties of England (including
Yorkshire).
from tiller to tiller, or from plant to plant, and
thereby increase the extent of crop damage. The
base of each infested shoot bears a ragged hole,
surrounded by discoloured tissue. Larvae are
usually fully grown by mid-May. They then enter
the soil to pupate, and adults emerge a few weeks
later. There is just one generation annually.
DESCRIPTION
Adult female
6-8 mm long, dull yellowish-grey;
legs
partly brown.
Adult male
6-8 mm long,
dark brown;
legs
black
(Plate 9e).
Egg 1.8 x
0.3 mm, elongate-oval, white and ribbed
longitudinally. Larva up to 12 mm long, whitish
to creamish-white, pointed anteriorly and blunt
posteriorly
(Plate 9f);
head
retracted into
prothorax;
anterior spiracles
fan-like, with seven
to eight lobes;
posterior spiracles
prominent;
pos-
terior papillae
prominent
(Fig. 266b)
(cf. yellow
cereal fly,
Opomyza florum,
p. 183; late-wheat
shoot fly,
Phorbia securis,
p. 201).
Puparium
6-
8 mm long, brown and barrel-like;
posterior pa-
pillae and spiracles
prominent
(Fig. 267).
BIOLOGY
Adults occur from June onwards. Eggs are laid
on bare soil in July or August. The females select
either fallow land, recently cultivated fields or
bare soil beneath the leaf canopy of existing
crops such as potato or sugar beet. Sites with
well-structured soils are preferred. The eggs
hatch in the following January or February.
Larvae die within a few days in the absence of
suitable host plants. On sites where cereals have
been drilled, each larva bites its way into the base
of a plant, just below soil level, and enters the
central shoot to begin feeding. Larvae develop
through three instars, and older larvae move
Delia echinata
(Seguy)
Spinach stem fly
This species is a locally important pest of
spinach. Infested foliage becomes distorted, the
