Agriculture Reference
In-Depth Information
grafts may wilt and die; damage caused by late
summer and autumn larvae tends to be most
significant. The minute, c. 2 mm long, dark red-
dish-brown adults occur from May onwards, and
there are typically three generations each year.
Eggs are inserted in the slits in the bark of newly
budded or grafted stock. They hatch in about a
week. The larvae then feed in small groups for
up to 3 weeks. Fully grown larvae, which are
salmon-pink to reddish-orange and up to c. 3 mm
long, drop to the ground to pupate in small co-
coons spun in the soil. Adults emerge 2-3 weeks
later. Larvae of the final generation complete
their development in the autumn, overwinter in
their cocoons and pupate in the spring.
sites are particularly liable to be attacked. The
larvae feed deeply within the florets and 'attack'
the developing grain (seed) producing tissue-
dissolving enzymes. The larvae usually occur
singly or in small numbers (cf. yellow wheat blos-
som midge,
Contarinia tritici,
p. 169). Affected
grains are misshapen and discoloured; also, they
do not enlarge fully and the loosened seed coat
often splits. If three or more larvae are associ-
ated with a single grain, the inner tissue will be
destroyed completely. Although heavy infesta-
tions cause yield reductions, the pest is of great-
est significance for its overall effect on grain
quality, especially as damaged grains may be in-
vaded by secondary fungal pathogens.
BIOLOGY
Adult midges appear in June. After mating at
emergence sites, the females migrate to new host
crops to lay eggs. They rest by day, at the base
of the crop, and are active mainly at dusk,
especially in warm, calm conditions. The eggs
are deposited in the florets, singly or in small
batches; typically, the females select ears which
are fully emerged from the enclosing flag-leaf
sheath (Growth Stages 55 onwards) (cf. yellow
wheat blossom midge,
Contarinia tritici,
p. 169).
The eggs hatch within a few days at normal sum-
mer temperatures. Surviving larvae, often just
one from each egg batch as mortality of eggs is
often high, then feed for up to a month. Final-
instar larvae retain the skin of the penultimate
stage and such larvae, which appear superficially
pupa-like, often remain within the ear up to har-
vest time, especially under dry conditions. Fully
grown larvae (which, unlike those of
C. tritici,
do
not jump) enter the soil, where they form co-
coons and eventually overwinter. There is just
one generation annually. Diapausing larvae are
known to survive in the soil for many years be-
fore pupating and producing adults.
Resseliella
sp.
Bean stem midge
This undescribed species of
Reselliella
is a minor
pest of field bean and was first reported, in the
early 1980s, in eastern England. First-generation
adults appear in late May and June. Eggs are
then laid in stem lesions, especially on winter-
sown beans. The larvae, which gradually change
in appearance from translucent whitish to deep
orange-red, feed gregariously in rows immedi-
ately below the epidermis; they occur mainly
from mid-June to mid-July, and their feeding
sites typically appear as black patches running up
the stem. Fully grown larvae drop to the ground,
pupate in the soil and a second generation of
midges emerges from mid-July to mid-August.
The fungus
Fusarium
is associated with the larval
feeding sites and, where significant fungal
growth develops, infested plants may become
lodged. First-brood larvae are associated mainly
with winter beans, as spring-sown bean plants
have relatively few stem lesions when egg-laying
females of the first generation are active.
Sitodiplosis mosellana
(Gehin)
Orange wheat blossom midge
DESCRIPTION
Adult
1.5-2.5 mm long, reddish-orange to brick-
red and relatively stout-bodied.
Egg
minute,
reddish to orange-yellow, sausage-shaped.
Larva
up to 2.5 mm long, reddish to orange-yel-
low, tapering both anteriorly and posteriorly;
This widespread and sporadically important pest
occurs on barley, rye and wheat; second and sub-
sequent winter wheat crops growing in sheltered
