Agriculture Reference
In-Depth Information
harvest; this is a particular problem on crops sent
for freezing where only a small proportion of
affected buttons may be sufficient for consign-
ments to be rejected.
Cauliflower:
light attacks
are sufficient to reduce curd size and, hence,
yield of autumn cauliflowers but winter crops are
rarely affected.
Chinese leaf, swede and turnip:
larvae cause minor damage to roots but may also
feed within the growing points to produce
multiheaded plants.
Radish:
fibrous roots are
destroyed, weakening host plants, and the bul-
bous tap root may become riddled with tunnels
(Plate 10a),
rendering the crop unmarketable;
superficial root damage may be sufficient to
make crops unsuitable for human consumption.
Wallflower and other ornamentals:
attacked
plants wilt in warm, dry weather and make poor
growth; small plants may collapse and die.
and ribbed longitudinally.
Larva
up to 10 mm
long, creamish-white;
head
deeply retracted into
prothorax;
posterior papillae
prominent, the
middle pair beyond the spiracles distinctly bifid
(Fig. 266d)
(cf.
Delia platura,
p. 199, etc.).
Puparium
6-7 mm long, elongate-oval, reddish-
brown.
Delia floralis
(Fallen)
Turnip root fly
This northerly distributed species occurs in many
parts of continental Europe and in northern
England and Scotland. The larvae attack various
vegetable brassicas and oilseed rape but are most
often associated with swede and turnip crops.
They feed deeply within the hearts of host plants
from September onwards, and there is usually
just one extended generation annually. Adults
(6-8 mm long) are essentially similar in appear-
ance to those of
Delia radicum
(above); the lar-
vae are distinguished from those of
D. radicum
by slight differences in the papillae surrounding
the posterior spiracles, none being bifid.
BIOLOGY
Individuals overwinter as pupae within puparia.
Adults emerge in the spring, from mid-April
onwards, but the precise timing of their appear-
ance depends upon temperature. Eggs are de-
posited in the soil close to the stems of host
plants; the period of egg laying often coincides
with the commencement of flowering of the com-
mon field-side weed
Anthriscus sylvestris.
Eggs
hatch 3-7 days later, and the larvae immediately
attack the roots of nearby host plants. They feed
for 3-4 weeks and then, when fully grown, move
away through the soil for a few centimetres be-
fore pupating. Adults of the second generation
appear in late June and July, and those of the
third from mid-August onwards. However, the
two generations tend to overlap so that subse-
quent egg laying can occur at virtually any time
from July to September. Although most eggs are
laid in the soil, a few may be placed on the lower
leaves of host plants. Larvae emerging from the
latter may attack the stems and growing points or
feed in the major leaf veins. Eggs are also depos-
ited between the outer leaflets of developing
Brussels sprout buttons, usually on those close to
the base of the stems of early-maturing cultivars.
Delia florilega
(Zetterstedt)
A bean seed fly
This pest attacks French bean, runner bean, bulb
and salad onions, and causes the same kind of
damage as
Delia platura
(q.v.). The larvae are
relatively slender-bodied, with a thin, semi-
transparent body wall, through which the pinkish
gut contents are clearly visible; the mouthparts
(cephalopharyngeal skeleton) are prominent
and the head only partly retracted into the
prothorax (cf. onion fly,
D. antiqua,
p. 197); the
posterior papillae are also particularly promi-
nent (cf.
D. platura,
p. 199).
Pegomya hyoscyami
(Panzer)
Mangold fly
This is a widespread and common but usually
minor pest of mangold and sugar beet; infes-
tations also occur on red beet and spinach. The
larvae (known as 'beet leaf miners') feed within
DESCRIPTION
Adult
6-7 mm long, mainly grey to
blackish.
Egg
1mm long, elongate-oval, white
