Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 168

376

in the spring, usually in May, there being just one
generation annually. Leaves with galled stalks fail to
develop properly, often becoming distorted and
noticeably hairy; the underside of the midrib might also
be swollen. Heavy attacks of this pest can prevent trees
flowering. However, the galls are usually most common
on sucker growth around the base of older trees, and this
reduces the importance of infestations.

Dasineura crataegi (Winnertz) ( 376-378 )
Hawthorn button-top midge
A generally common pest of hawthorn ( Crataegus ),
infestations often occurring in abundance on hedges and
in nurseries. Eurasiatic. Widely distributed in Europe. 376 Larvae of hawthorn button-top midge ( Dasineura

crataegi ).

DESCRIPTION
Adult: 2.0-2.5 mm long; brownish with darker
crossbands on the abdomen. Larva: up to 3 mm long;
reddish but whitish when young.

377

LIFE HISTORY
Adult midges appear in April or May, females
depositing eggs in the tips of young shoots of hawthorn.
Attacked shoots fail to elongate and, instead, develop
into compact, rosette-like galls; these galls eventually
turn black, remaining on the host plants long after the
causal larvae have departed. The galls are often noted
on nursery stock, and are most numerous on regularly
trimmed hedges which provide an abundance of suitable
egg-laying sites. Several larvae develop within each
gall, individuals becoming fully fed in 2-3 weeks. They
then drop to the ground and pupate inside silken
cocoons, adults emerging shortly afterwards. There are
further generations during the summer, autumn larvae
overwintering in their cocoons and pupating in the
spring.

377 Gall of hawthorn button-top midge ( Dasineura crataegi )
on Crataegus .

378

DAMAGE
The galls disfigure host plants; also, by interfering with
normal shoot development, they affect the shape and,
hence, quality of nursery stock. Leaves immediately
below the main galls often unfurl but remain disfigured
by numerous red pimples. Attacks on established plants
are rarely troublesome, even when infestations are heavy,
but damage to nursery stock might be unacceptable.

378 Hawthorn button-top midge ( Dasineura crataegi )
damage to leaf of Crataegus .