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Adelgidae : Adelgini : Adelges nordmannianae
 

 

Adelges nordmannianae

Silver-fir woolly adelgid

On this page: Identification & Distribution Biology & Ecology Other species on the same host Damage & Control

Identification & Distribution

Adelges nordmannianae induces terminal (=branch-end) galls on its primary host, Caucasian (= Oriental) spruce (Picea orientalis, see first picture below). The galls are 2-15 mm long, globular, pinkish, strawberry-like when young, but later becoming greenish with red or purple coloration at the bases and/or tips of the scales. The gallicola of Adelges nordmannianae which develops in the gall (see second picture below) has the body and wings at first greenish, darkening in a few days. The wings are strongly curved. The antennae have 5 segments (see third picture below), and large rhinaria on segments IV and V which extend half the length of the segment, or even more in the case of segment IV. Segment V is much narrower than the other segments and distinctly cigar-shaped. The rhinarium on III is almost half the length of the segment and extends more than half way round it. Adult body length is 1.1-1.54 mm, body width is 0.55-0.66 mm.

The secondary host of Adelges nordmannianae is fir (Abies). Nymphs overwinter on fir and, on maturing, deposit clusters of brownish-orange eggs. These hatch at bud-burst and the reddish brown 'crawler' disperse over the young needles (see first picture below). The first instar larva of the sistens morph (the overwintering neosistens stage) is the stage often used for identifying Adelges nordmannianae. The wax pore plates on the inner margins of meso- and metathoracic spinal sclerites contain numerous small rounded pits, arranged in 2-4 areas, the most central area containing 7-12 pits. The total number of pits in the central areas of the spinal wax pore plates of the meso- and metathorax together with abdominal tergites I-III (i.e. 10 central areas) is 57-104 (cf. Adelges piceae, which has 18-63 pits in the 10 central areas). There are then several parthenogenetic generations of multiplication, with both apterae and alatae produced. The second picture below shows mainly immature Adelges nordmannianae alatae (which are unwaxed) and a few apterae (waxed).

Where the primary host is present (primarily the Caucasus mountains of Russia & Turkey), Adelges nordmannianae has a two year life cycle, host alternating between its primary host, Caucasian spruce (Picea orientalis), and its secondary host, Nordmann fir (Abies nordmanniana). On its primary host it produces small rounded terminal galls. The winged forms that emerge from the galls migrate to fir where it has a series of parthenogenetic generations. This adelgid has been introduced to much of Europe, North America and New Zealand where it is anholocyclic on a variety of secondary hosts, including Nordmann fir and silver fir (Abies alba).

 

Biology & Ecology

The gall of Adelges nordmannianae is very distinctive. In most countries it is only likely to be found on Caucasian spruce (Picea orientalis), although it has occurred occasionally on other spruce species.

Carter (1971) working in the 1960s reports finding young fundatrices of Adelges nordmannianae on Picea orientalis at Bedgebury, towards the end of March. Their presence was detected by searching the undersides of the buds for white wax-wool secretions. Towards the end of April and early May discrete blobs (about 1.5 mm diameter) of wax-wool were to be seen, partially concealing the adult fundatrix and eggs. The galls developed from the buds fed on by the fundatrices, first appearing towards the end of May. The nymphs emerging from the eggs laid by the fundatrix develop in the galls reaching fourth instar by June. The final instar nymphs (see first picture below ) then vacate the gall with the final moult taking place on the gall surface.

Vacated galls can be recognized by the covering of white exuviae over the gall (see second picture above).

Carter (1971) noted that the gallicolae (see picture above) emerged between mid-June and early August similar to the timing we observed in 2019.

 

Other species on the same host

Primary hosts

Adelges nordmannianae has been recorded from 4 Picea species (Picea abies, Picea glauca, Picea omorika, Picea orientalis).

Blackman & Eastop list about 170 species of aphids as feeding on spruces (Picea) worldwide, and provide formal identification keys.

Of the 14 aphid species Blackman & Eastop list as feeding on Caucasian spruce (Picea orientalis) worldwide (Show World list), Baker (2015) lists 12 as occurring in Britain: (Show British list).

Secondary hosts

Adelges nordmannianae has been recorded from 11 Abies species.

Blackman & Eastop list 47 species of aphid as feeding on true firs (Abies species) worldwide, and provide formal identification keys.

  • Blackman & Eastop list 10 species of aphid as feeding on Nordmann fir (Abies nordmanniana) worldwide, and provide formal identification keys. (Show World list). Of those aphid species, Baker (2015) lists 7 as occurring in Britain: (Show British list).

  • Blackman & Eastop list 15 species of aphid as feeding on silver fir (Abies alba) worldwide, and provide formal identification keys. (Show World list). Of those aphid species, Baker (2015) lists 8 as occurring in Britain: (Show British list).

     

    Damage and control

    Nordmann fir is the main species used for Christmas tree production in many Northern European countries. Adelgid attack has caused important losses of trees in plantations. Mass attacks are rare and only occur outside the natural distribution area of the particular fir species. Within the Caucasus mountains populations are kept low by natural enemies.

    Acknowledgements

    We especially thank the UK Forestry Commission Bedgebury Pinetum for their kind assistance, and permission to sample.

    Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

    Useful weblinks

    References

    • Carter, C.I. (1971). Conifer Woolly Aphids (Adelgidae) in Britain. Forestry Commission Bulletin No. 42. Forestry Commission, London Full text