Agriculture Reference
In-Depth Information
ous, lemon-yellow larvae (cf.
Contarinia
geniculati,
below) feed on the seeds, sheltered
within the glumes. Adult midges are active from
late May onwards, eggs being deposited within
the developing florets. The larvae feed during
the summer for up to 4 weeks. Fully grown indi-
viduals then enter the soil to overwinter, each
in a silken cocoon. Pupation takes place in the
spring, shortly before the appearance of the
adults. Although seed production is reduced, at-
tacks are rarely of economic importance.
which become swollen basally and fail to open.
Heavy infestations cause significant seed loss,
damage often being of considerable importance
in continental Europe but of little significance in
the British Isles. The yellowish-grey adults occur
from May onwards, and development from egg
to adult takes approximately 5-6 weeks; there
are two or three generations annually.
Contarinia merceri
Barnes
A foxtail midge
Contarinia geniculati
(Reuter)
This generally common midge is associated with
meadow foxtail. Infestations sometimes cause
economic damage to seed crops, especially
those growing in sheltered sites. Adults occur in
late May and early June, eggs being deposited
within the florets. The golden-yellow larvae,
up to 2.5 mm long, which have a small sternal
spatula, feed gregariously within the florets
(cf.
Contarinia geniculati,
above, and
Dasineura
alopecuri,
p. 171); they destroy the seeds so that
empty glumes are present at harvest. Individuals
are fully grown within a month. They then enter
the soil to spin cocoons. A few of the larvae may
pupate in the summer to produce a partial sec-
ond generation in the autumn; most, however,
overwinter and pupate in the spring.
This generally common grass midge attacks the
florets of both cocksfoot and meadow foxtail.
The larvae feed singly within the florets (cf.
Contarinia merceri,
below) and there are up to
two generations each year. In common with
those of other species, they contribute to yield
losses in seed crops. The fully grown larvae are
pinkish-yellow and, unlike those of related spe-
cies, lack a sternal spatula. In common with those
of
Dasineura alopecuri
(p. 171), the larvae often
remain within infested seeds after harvest.
Contarinia humuli
(Theobald)
Hop strig midge
Infestations of this widely distributed but un-
common pest are sometimes reported in hop gar-
dens; the whitish larvae (known as 'hop strig
maggots') feed gregariously within the cones,
usually from mid-August to mid-September. In-
fested strigs become riddled with tunnels and
blackened, heavily infested cones turning brown.
Attacks are most often reported on cultivars
Fuggle and Tutsham. Adult midges occur in late
July and August, and there is just one generation
annually.
Contarinia nasturtii
(Kieffer)
Swede midge
Infestations of this widely distributed midge
occur on various members of the Brassicaceae,
including cabbage, cauliflower and fodder
brassicas; however, they are most important on
swede, including fodder crops. The small, deli-
cate, yellowish adults appear in May and June,
and eggs are then deposited in the young tissue
of host plants. The eggs hatch in about a week
and the pale, yellowish-white larvae (up to
2.5 mm long) then feed gregariously. They cause
a swelling of flowers, crinkling of leaves ('crum-
ple leaf symptom) and, often and most signifi-
cantly, death of the main growing point; the
latter damage leads to the proliferation of sec-
ondary shoots ('many neck' symptom). Larval
Contarinia medicaginis
Kieffer
Lucerne flower midge
Infestations of this widely distributed midge
occur on lucerne. The whitish larvae (up to 2mm
long) feed gregariously within the flower buds,