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Larch adelgid, Larch woolly aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host Damage & Control
Identification & Distribution:
Adelges laricis galls on spruce (see first picture below) are waxy, creamy and relatively small. These galls mature in June-July. The winged female gallicola of Adelges laricis (see second picture below) which matures on spruce is greyish to blackish, with a body length of 1.9-2.0 mm. Antennal segments IV and V of the gallicola do not have deep constrictions at the articulating surfaces, so that segments III to V appear fused. The rhinarium on segment III is narrow and angular. Each rhinarium extends at least half way round the circumference of its segment. The gallicolae migrate to larch where they lay eggs.
First image courtesy AfroBrazilian under a Creative Commons Attribution-Share Alike 3.0 Unported license.
The eggs hatch to give blackish-grey apterous sistens females which on maturity lay large clusters of eggs. These develop to give wingless and winged exules which are covered in white woolly wax (see third picture above). The winged female that matures on larch is dark green, with a greyish-green head and thorax and a body length of 1.0-1.5 mm. The winged females migrate back to spruce and lay eggs which develop to sexual forms. After mating eggs are laid which hatch in autumn.
The larch adelgid host alternates between the primary host Picea (spruce) and the secondary host Larix (larch). The larch adelgid was originally found in central Europe, but Adelges laricis is now widespread throughout that continent and has been introduced to North America.
Biology & Ecology:
Females on spruce hatch from fertilized eggs in autumn, and the young larvae overwinter on spruce twigs. In spring they feed at the bud scale bases inducing a gall (see picture below).
Image courtesy AfroBrazilian under a Creative Commons Attribution-Share Alike 3.0 Unported license.
The galls mature in summer to give greyish to black winged females known as gallicolae (see top of page right). These fly to larches, settle on the needles and deposit eggs.
The eggs hatch to give blackish or purplish grey nymphs that overwinter on one-year-old larch shoots near bud. (see picture below). These nymphs mature in April to blackish grey females (sistens) that reproduce parthenogenetically and deposit unprotected clusters of eggs at base of leaf spurs (see picture below).
Nymphs emerging from these eggs spread out on to the larch needles, maturing into wingless or winged adults a month later.
Wingless (and some winged) females continue to reproduce on larch, producing one or more generations and vast quantities of wax wool and large globules of honeydew. The specimen below right has been dewaxed artificially to show the nymphal winged form. The wing buds are just visible laterally.
Winged forms migrate back to spruce, especially sitka spruce, and lay eggs which develop as sexual males or females. These mate, and the females lay fertilized eggs which hatch in autumn and start the cycle again.
Mitchell & Maksymov (1977) have recorded two predators - a syrphid (Cnemodon) and a cecidomyiid Aphidoletes abietis - feeding on developing gallicolae within the tightly closed galls of both Adelges laricis and Adelges abietis. The syrphid larva enters the gall before it is closed, but the cecidomyiid larva enters the gall after it has closed, and causes the gall to open prematurely when the predator reached the last larval instar.
Other aphids on same host:
Adelges laricis has been recorded from 10 Picea species.
Blackman & Eastop list about 170 species of aphids as feeding on spruces (Picea) worldwide, and provide formal identification keys.
Adelges laricis has been recorded from 7 Larix species.
Damage & Control:
The main damage caused by Adelges laricis is to provide an entry route for fungi to larch trees. Skarmoutsos & Millar (1982) found that the fungus Meria laricis invaded needles of Larix x eurolepis at the feeding sites of Adelges and caused premature needle fall. Several other fungi were also isolated from larch needles attacked by aphids. Labanowski & Soika, 1999 achieved good control of Adelges laricis using sprays of acetamiprid, imidclopridand other older insecticides.