Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 169

379

379 Violet leaf midge ( Dasineura affinis ) galls.

Dasineura abietiperda (Henschel)
This widely distributed midge attacks the young growth
of spruce ( Picea ), including Norway spruce ( P. abies ).
Adults appear in April and May, the females depositing
eggs near the growing points of the new shoots. The
reddish larvae (up to 3 mm long) feed singly, each
within a cavity formed in the bark or new wood; they
will also burrow into the buds at the shoot tips. The
larvae usually complete their development in the
autumn. They then overwinter, pupating in the spring
shortly before the emergence of the adults. Several galls
usually occur close together, affected shoots remaining
shorter than normal, bearing fewer needles and
becoming slightly bent. Heavy infestations cause
considerable damage to young trees; losses are of
particular importance on spruces grown as Christmas
trees.

six weeks; they then pupate in silken cocoons, still
within the gall, adult midges emerging about 10-12 days
later. There are usually four overlapping generations
annually on outdoor plants, larvae of the final brood
overwintering and completing their development in the
spring. In greenhouses, there are commonly additional
generations and, if conditions are suitable, breeding can
continue throughout the year.

Dasineura alpestris (Kieffer)
syn. D. arabis (Barnes)
Arabis midge
A potentially important pest of certain kinds of Arabis ,
including rock cress ( A. alpina ), damaging infestations
sometimes occurring in gardens and nurseries. Adults
appear from May onwards, the females depositing
reddish eggs between the leaf tissue in the developing
buds. These eggs hatch within a few days, and pinkish
or reddish larvae then feed in compact but open galls
which develop as the leaf bases become enlarged and
swollen. There are commonly 20-30 larvae in each gall,
sometimes considerably more. Fully grown larvae
pupate in white cocoons spun either within the gall or in
the soil. Midges of the next generation emerge shortly
afterwards. There are three or four generations each
year, larvae of the final generation overwintering in
their cocoons and pupating in the spring. Heavily
infested plants produce few flowers, their central
crowns are destroyed and any new growth is limited to
weak, lateral shoots.

Dasineura affinis (Kieffer) ( 379 )
Violet leaf midge
A widely distributed, important and often persistent pest
of wild and cultivated violet ( Viola ). Infested plants
become stunted and malformed, with flower production
seriously affected if not entirely prevented; in severe
cases, plants might eventually die. Adult midges occur
from May onwards, depositing eggs in the rolled
margins of young leaves and, occasionally, in the
developing flowers. Infested tissue fails to unroll and
often becomes swollen into conspicuous galls, within
which several whitish to whitish-orange larvae (each up
to 2 mm long) develop. Larvae are fully fed in about