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Green spruce gall adelgid; Spruce-larch gall adelgidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host Damage & Control
Identification & Distribution
Of the three closely related adelgid species (Adelges viridis, Adelges viridana & Adelges abietis) Adelges viridis is the only holocyclic species. It host alternates between spruce (Picea) and larch (Larix). On spruce in May the fundatrix (see first picture below, with her asexually-produced eggs) induces an ellipsoidal, 'pineapple gall' (second picture below) - usually about 15-20 mm in length, albeit its length less than 1.5 times the width.. The spruce needles on the gall are often bent and are a slightly paler green than on a normal shoot. The slits to gall chambers are often orange-red or deep pink before opening. There is usually only a single gall at the shoot tip, with no growth beyond it (cf. Adelges abietis which often has several galls together at the base of adjacent shoots, and plant growth continues beyond the gall). The offspring of the fundatrix inside the gall are reddish-yellow to brown, powdered with white wax. The gall chambers open in June-July (cf. Adelges abietis whose galls open in August-September) to release the yellow-brown winged gallicolae (not pictured). The Adelges viridis gallicola has 5-segmented antennae and five pairs of abdominal spiracles and is not distinguishable morphologically from the gallicola of Adelges abietis.
Third image above copyright Milan Zubrik, Forest Research Institute, Slovakia, Bugwood.org under a Creative Commons Attribution-Noncommercial 3.0 License.
Adelges viridis gallicolae migrate to larch where they lay eggs. These hatch, then overwinter as young larvae. The following year the young nymphs first become evident on the new growing larch needles in mid-April as they develop to apterous sistentes. These do not produce much wax-wool and their pale greenish colour makes them difficult to locate. In early May the points on each needle where they have fed turn yellow and becomes slightly swollen, producing a characteristic kinking of the needle (see third picture above). The offspring of the sistens develop in May-June (earlier than other species) either to apterous forms which remain on larch or to winged sexuparae (also in the third picture above) which fly back to spruce. These winged sexuparae can be distinguished from the winged gallicola of Adelges abietis (see Carter, 1971) by several characteristics:
The offspring of sexuparae hatch into the summer sexual forms which mate, and the female lays eggs. These eggs hatch to give the fundatrices which induce the next generation of pineapple galls.
The green spruce gall adelgid may be found galling several spruce species including Norway spruce (Picea abies), sitka spruce (Picea sitchensis), white spruce (Picea glauca) and Caucasian spruce (Picea orientalis). It host alternates to larch (Larix species). Adelges viridis is found throughout Europe, and is also found in China.
Other aphids on the same host
Adelges viridis has been recorded from 14 or 15 Picea species.
Blackman & Eastop list about 170 species of aphids as feeding on spruces (Picea) worldwide, and provide formal identification keys.
Adelges viridis has been recorded from 4 Larix species (Larix decidua, Larix × eurolepis, Larix kaempferi, Larix sibirica).
Damage and control
The green spruce gall adelgid may cause serious damage to spruce grown for Christmas trees. The green pineapple galls spoil the tree's appearance. Although nursery trees of less than four years of age are rarely badly damaged, early infestation in the young plant may result in serious damage as it gets older. Adelges viridis can also cause defoliation of young larch.