Agriculture Reference
In-Depth Information
Haplodiplosis marginata (von Roser)
Saddle-gall midge
become an important pest of cultivated mush-
rooms. The larvae contaminate the sporophores;
they also introduce a bacterium that produces
brown longitudinal stripes on the stipes and tiny
black globules of liquid on the gills. Crop losses,
especially of the later flushes, are often heavy.
The saddle-gall midge is a sporadic and locally
important pest of barley, oats and wheat, but
causes most damage on heavy-land sites where
cereals are grown intensively; infestations also
occur on various grasses, including Elytrigia
repens. The larvae form distinctive galls on the
stems of infested plants. If numerous, the galls
(which often occur in rows along the stem) have
a direct effect on cropping, reducing grain size
and plant yields by 10% or more. The galls also
weaken stems, so that affected plants may lodge
or break off in a strong wind. Damage tends to
be concentrated around the edges of fields. In
the British Isles, this pest has proved of most
significance in central and eastern England.
BIOLOGY
Breeding populations in mushroom beds consist
of paedogenetic larvae, which feed on fungal
mycelium and also invade the sporophores. The
larvae become fully grown in about 5 days. The
larval gut then opens to expel a faecal tube about
10 mm long (cf. mushroom midge, Mycophila
barnesi, p. 175), after which the larvae (known as
'mother' larvae) moult into sedentary 'hemi-
pupae' within which several embryos develop;
new individuals emerge about 2 days later, each
as a "daughter' larva, about 1mm long. Under
ideal conditions. 14 'daughter' larvae are pro-
duced from each 'mother' larva in just under a
week, and larval populations build up extremely
rapidly; many thousands can occur in a mere
handful of casing material. Under dry conditions,
the larvae will clump together to form sticky
seething masses, often measuring many milli-
metres across. These larvae are frequently trans-
ported to previously clean mushroom beds on
workers' clothes, equipment and tools, and are a
major source of new infestations; larvae may also
be introduced into mushroom houses in contami-
nated peat. If breeding conditions become
unfavourable, fewer than normal individuals are
produced within the 'mother' larvae, and the
embryos develop into thick-walled resting
stages, capable of surviving for well over a year.
Larval infestations in mushroom beds may con-
tinue to develop for many generations but,
eventually, usually about 2 months after spawn-
ing, 'imago' larvae appear. These pupate after a
single moult and, about 5 days later, adult midges
emerge. The adults often occur in vast numbers
but are harmless. Also, most are female and few
become fertilized, so the risk of their initiating
further infestations is slight.
BIOLOGY
Adults appear in late May and early June. Eggs
are then deposited in chain-like groups, usually
on the upper surface of the leaves of wheat and
other hosts. In total, each female may deposit up
to 200 eggs, in batches of about 25. The eggs
hatch 1-2 weeks later. The larvae then move into
the shelter of the leaf sheath and begin to feed on
the stem, each forming a characteristic saddle-
like depression or gall. Fully grown larvae even-
tually drop to the ground, usually in late July, to
overwinter in the soil, each in a silken cocoon.
Most surviving larvae pupate in the spring, after
first vacating their cocoons and moving closer to
the surface; a smaller number of larvae, however,
remain in diapause for a further year or more.
There is just one generation annually.
DESCRIPTION
Adult 4.0-5.5 mm long, blood-red. Egg 0.3 mm
long, sausage-shaped, red and translucent.
Larva up to 5 mm long, orange-red to red; sternal
spatula broad, with a blunt tip (Fig. 246c).
Heteropeza pygmaea Winnertz
Mushroom cecid
DESCRIPTION
Adult female orange, weak-bodied, with
sclerotized spermothecae visible towards the
This midge is generally common and widespread
in decaying vegetation and rotting wood, and has
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