Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 170

380

381

380 Galls of ash midrib pouch-gall midge ( Dasineura fraxini )
on Fraxinus .

381 Ash midrib pouch-gall midge ( Dasineura fraxini ) damage
to leaves of Fraxinus .

383

382

382 Young galls of honey locust gall midge (Dasineura
gleditchiae) on leaves of Gleditsia .

383 Galls of honey locust gall midge ( Dasineura gleditchiae )
on leaves of Gleditsia .

Dasineura fraxini (Bremi) ( 380-381 )
syn. D. fraxini (Kieffer)
Ash midrib pouch-gall midge
This widely distributed and often common species
causes the underside of the leaves of ash ( Fraxinus
excelsior ) to swell into conspicuous galls (25-30 mm
long) along either side of the midrib. Development of
galls commences in May or June. They usually contain
from four to eight orange-coloured larvae, each located
in its own cell. Maturity is reached in September. The
upper surface of the gall then splits open longitudinally,
the fully fed (2-3 mm long) larvae dropping to the
ground and overwintering in the soil. Pupation occurs in
the spring, adult midges emerging shortly afterwards.
Infestations occur on both young and mature trees;
although affected leaves might eventually turn brown
and die prematurely, damage does not affect shoot
growth.

Dasineura gleditchiae (Osten-Sacken) ( 382-383 )
Honey locust gall midge
Of North American origin but now well established on
honey locust ( Gleditsia triacanthos ) in various parts of
Europe, including (from the 1980s onwards) southern
England. Adults emerge from late May onwards. Larvae
feed gregariously on the leaves, causing them to
develop into yellowish-green to purplish-red, pod-like
galls that eventually turn brown. Infested shoots are also
distorted, the galls often causing severe disfigurement.
Pupation occurs within the galls, adults appearing
shortly afterwards. There are several overlapping
generations throughout the summer, development from
egg to adult being completed in 3-4 weeks. Fully grown
larvae are whitish and 3.0-3.5 mm long; those reared in
the autumn overwinter in subterranean cocoons,
pupating in the spring. The pest can also persist in the
soil for more than a year before producing adults.