Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 89

183

Adelges laricis (Vallot) ( 183-185 )
syn. A. coccineus (Ratzeburg)
Larch adelges
An often common pest of larch ( Larix ), including
ornamentals, but mainly present on older trees; also
gall-forming on spruce ( Picea ). Originally restricted to
the central Alps but now widespread throughout
Europe; also introduced into North America.

DESCRIPTION
Alate female [ex: larch]: 1.0-1.5 mm long; dark green,
with a greyish-green head and thorax; fore wings
c . 0.5 mm long. Alate female [ex: spruce]: 1.9-2.0 mm
long; greyish to blackish; fore wings c . 0.6-0.7 mm
long. Egg: greyish black, coated in whitish wax.

183 Larch adelges ( Adelges laricis ) on Larix .

184

LIFE HISTORY
Blackish or purplish-grey nymphs overwinter on the
bark of one-year-old larch shoots, often settled close to
a bud. They mature in April, appearing blackish grey,
and then deposit unprotected clusters of eggs at the base
of the leaf spurs. Nymphs developing from these eggs
feed on the new foliage, turning into either winged or
wingless adults about a month later. The former then
disperse to spruce trees, including Sitka spruce ( Picea
sitchensis ), while the latter continue to breed on the
larch needles, producing vast quantities of waxen
'wool' and sticky honeydew. This honeydew commonly
accumulates as large globules amongst the protective
canopy of waxen fibres. Individuals migrating to
spruces give rise to wingless sexual forms and, in the
following spring, gall-forming nymphs develop. Galls
formed by this species on spruce are characteristically
waxy, creamy and relatively small ( c . 10-15 mm long).
They mature in the summer, and the fully winged
gallicolae which emerge, fly back to larches, to settle on
the needles and eventually deposit eggs.

184 Galls of larch adelges ( Adelges laricis ) on Picea .

185

DAMAGE
Larch: infested foliage is disfigured with masses of
white, waxen 'wool'. The needles become discoloured
and distorted, heavily infested trees often appearing
blue; attacks may also lead to premature loss of needles
and to die-back of shoots. Spruce: galls sometimes
prevent further shoot growth.

185 Larch adelges ( Adelges laricis ) on Larix .