Agriculture Reference
In-Depth Information
(b)
Fig. 246
Spatulas of various midge larvae: (a) pea midge,
Contarinia pisi;
(b) yellow wheat blossom midge, C.
tritici;
(c) saddle gall midge,
Haplodiplosis marginata;
(d) orange wheat blossom midge,
Sitodiplosis mosellana.
in the soil and most of these pupate in May or
June; some larvae, however, remain in their co-
coons for several years before eventually pupat-
ing and producing adults.
see p. 92
et seq.,
and these are sometimes mis-
taken for midge larvae.) Fully grown larvae
eventually 'jump' to the ground and enter the
soil; they usually emerge from the ear ahead of
those of
Sitodiplosis mosellana
(larvae of both
species sometimes occur together). Under very
dry conditions, the larvae can become trapped
within the glumes but they often emerge in num-
bers following a shower of rain. A few larvae
may pupate whilst still within the glumes; others
which have succeeded in reaching the ground
may also pupate (without forming cocoons).
Such individuals give rise to a partial second
generation of adults that deposit eggs on
Elytrigia repens.
The majority of larvae, how-
ever, spin cocoons in the soil and either pupate in
the following May or early June (typically, first
emerging from their cocoons and moving closer
to the soil surface) or remain in diapause for up
to three seasons before eventually pupating.
Winter mortality of larvae is often considerable.
DESCRIPTION
Adult
greyish-brown with long legs and antennae;
wings
2mm long.
Egg
0.25mm long, translu-
cent, elongate-oval with a pointed tip.
Larva
up
to 3 mm long, dirty white;
sternal spatula
broad-
ened anteriorly and strongly cleft
(Fig. 246a).
Contarinia tritici
(Kirby)
Yellow wheat blossom midge
Infestations of this widely distributed midge oc-
cur on wheat and, less frequently, barley and rye
but are rarely of economic significance. The lar-
vae attack the floral parts (stigma and styles)
(cf. orange wheat blossom midge,
Sitodiplosis
mosellana,
p. 176), and usually prevent pollina-
tion and, thus, grain development. Heavily in-
fested ears have a flattened appearance.
DESCRIPTION
Adult
2-3 mm long, lemon-yellow to dusky-
yellow, with relatively large, black eyes and dusky
wings.
Egg
minute, golden-yellow and translu-
cent; sausage-shaped with a long stalk.
Larva
up
to 3 mm long, yellow, tapered anteriorly and blunt
posteriorly, the penultimate body segment with a
pair of chitinized tubercles;
sternal spatula
with a
rounded, bifid tip
(Fig. 246b).
BIOLOGY
Adult midges, although short-lived, sometimes
appear in vast numbers over cereal crops in
about mid-June. Eggs, typically in batches of up
to 30, are laid in the developing but unhardened
florets, as soon as the developing ear is exposed
(i.e. when the leaf sheath has split: Growth Stage
51); the females do not deposit eggs in hardened
florets. Eggs hatch 7-10 days later. The larvae
then feed gregariously, sometimes several hun-
dred in each infested ear, and complete their
development in approximately 3 weeks. (The
yellowish nymphs of cereal thrips,
Limothrips
spp., also occur in the ears of developing cereals,
Contarinia dactylidis
(Loew)
Cocksfoot midge
Infestations of this univoltine species occur on
cocksfoot. The small (up to 2mm long), gregari-
