Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 177

Parallelodiplosis cattleyae (Molliard)
Cattleya gall midge
This tropical midge sometimes occurs in European
greenhouses, initiating elongate or pea-like galls on the
aerial roots of orchids, including various species of
Cattleya and Laelia. The pest is usually of little
significance but the growth of heavily infested plants is
retarded. There are several generations annually, with
numerous orange-coloured larvae developing within
individual cells in each gall. Fully grown larvae pupate
in their cells. Pupae eventually protrude from the
surface of the gall following emergence of the adults.

LIFE HISTORY
Adults are active in the spring, depositing eggs in the
young leaves by inserting the ovipositor from below.
Eggs hatch in about three weeks; the larvae then mine
within the leaf tissue to form distinctive yellowish or
brownish blister-like mines on the underside of the
leaves. Where several larvae are present in the same
leaf, the blisters often coalesce and may eventually
occupy the complete leaf blade. Larvae overwinter
within the mines, completing their development in the
spring. They then pupate, midges appearing 2-3 weeks
later.

Resseliella oculiperda (Rübsaamen)
larva

DAMAGE
Larval mines are visible from above as discoloured
swellings, disfiguring the foliage and spoiling the
appearance of both specimen ornamentals and hedges.
Heavy infestations weaken host plants, infested leaves
dropping prematurely. Persistent attacks gradually
reduce the overall density of the foliage.

red bud borer
A local and usually sporadic pest of budded stock and
grafts, attacking rose ( Rosa ) and rosaceous fruit trees
such as apple. Widely distributed in Europe.

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DESCRIPTION
Adult: 1.4-2.0 mm long; dark reddish brown. Larva:
up to 3.5 mm long; salmon-pink to red, with a bilobed
spatula.

Oblodiplosis robiniae (Haldeman) ( 406 )
False acacia leaf midge
This invasive North American species first appeared in
Europe in 2003, in northern Italy. It has since spread
rapidly and is now firmly established on false acacia
( Robinia pseudoacacia ) in many parts of mainland
Europe. The pest has also been found in Japan and
Korea. Larvae (up to 4 mm long) are at first whitish and
translucent, but later turn yellow. They feed in tightly
rolled leaf edges, on average each gall containing about
two individuals. Infestations affect the appearance of
ornamental plants, and also cause premature leaf fall.
There are two or more generations annually.

LIFE HISTORY
Adults occur in three generations, in late May to late
June, July to early August and late August to early
September, depositing eggs in graft slits or cuts in the
bark of newly budded stock. Eggs hatch about a week
later. Larvae then feed in small groups on sap in the
cambium between the scion and stock. They are fully
fed in 2-3 weeks, each dropping to the ground to pupate
in a small cocoon a few centimetres below the surface.
Larvae of the autumn generation overwinter in their
cocoons and pupate in the spring.

DAMAGE
Infestations prevent grafts or buds from taking, so that
the scions or buds wither and die. Most damage is
caused by larvae which feed from August onwards,
when losses on unprotected nursery stock may be
considerable.

406

406 Galls of false acacia leaf midge ( Oblodiplosis robiniae ).