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Genus Adelges

Spruce gall adelgids

Species Overview: Adelges Adelges abietis Adelges cooleyi Adelges laricis Adelges piceae

Genus Adelges [Adelgidae]

Identification: Members of the genus Adelges are distinguished by having five pairs of abdominal spiracles, whereas members of the other genus of Adelgidae, Pineus, have only four distinct pairs. Adelges aphids are often identified from the shape of the galls on the primary host (spruce) which are cone-like, sometimes resembling miniature pineapples. Forms on the secondary host often produce abundant wax.

There are about 30 species of Adelges worldwide. The primary host of species with a sexual stage in their life cycle is spruce (Picea), and the secondary hosts are fir (Abies), larch (Larix) and other conifers (but not pine). The complete life cycle of these species takes two years. Several Adelges species have lost sexual reproduction and host alternation, and instead live all year on spruce or the (original) secondary host.

 

Adelges abietis (Eastern spruce gall adelgid)

Identification: The gall on spruce is known as a 'pineapple gall'. The mature gall (see first picture below) is ellipsoidal with its length less than 1.5 times the width and usually about 15-20 mm in length. The spruce needles on the gall are shorter than normal. The gall is only slightly paler green than a normal shoot. The slits to gall chambers are often orange-red or deep pink before opening. There are often several galls together at the base of adjacent shoots, and plant growth often continues beyond gall. The gall chambers open in August-September.

 

The winged female (gallicola) of Adelges abietis is yellow with 5-segmented antennae and five pairs of abdominal spiracles (see second picture above). The wingless female (pseudo-fundatrix) is yellowish-green to light green again with 5-segmented antennae.

The pineapple gall adelgid is mainly found on Norway spruce (Picea abies), but it can also occur on other Picea species including sitka spruce (Picea sitchensis) and white spruce (Picea glauca). It is distributed throughout Europe, and is also found in Morocco, India and North America.

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Adelges cooleyi (Cooley spruce gall adelgid, Douglas fir adelgid)

Identification: On spruce trees (Picea) Adelges cooleyi is most commonly identified by the gall it produces: which is elongated (it is more than 1.5 times as long as it is wide) and is often curved with long needles protruding from it. Adelges cooleyi galls are highly variable in colour, yellow-green, pink, red or even deep purple (see first picture below).

 

First image courtesy of Whitney Cranshaw, Colorado State University / copyright Bugwood.org  (CC BY 3.0 US ).
 
Second image by permission of Claude Pilon  copyright all rights reserved.

Winged females of Adelges cooleyi are reddish brown to purplish black (see second picture above). They are somewhat larger when originating on spruce (length 1.7-2.5 mm) than on Douglas fir (length 1.2-1.7 mm.).

On Douglas fir the most commonly seen morph is the apterous exule which is covered in white woolly wax (see picture above).

The cooley spruce gall adelgid typically has a two year life cycle alternating between spruce (Picea sitchensis, Picea pungens, Picea engelmanii) and Douglas fir (Pseudotsuga menziesii, Pseudotsuga macrocarpa). Host alternation is sometimes lost and the species remains on one host all year round. For example a form in Canada remains on Picea glauca) and forms in Europe and California remain on Pseudotsuga. Adelges cooleyi is native to western North America, but is now found throughout Europe and North America.

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Adelges laricis (Larch adelgid, Larch woolly aphid)

Identification: Adelges laricis galls on spruce (see first picture below) are waxy, creamy and relatively small. These galls mature in June-July. The winged female 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. 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 (see second picture below).

 

First image courtesy AfroBrazilian under a Creative Commons Attribution-Share Alike 3.0 Unported license.

On larch the most commonly seen morph is the apterous exule which is covered in white woolly wax (see picture below).

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.

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Adelges piceae (Balsam woolly adelgid)

Identification: The first indication that a fir tree is affected with balsam woolly adelgid is small patches of white wax wool on the bark (see first picture below). The white wax wool largely covers the developing and adult Adelges piceae. Under the wool Adelges piceae adults are less than 1mm long, blackish-purple and roughly spherical in shape (see second picture below).

 

Adelges piceae eggs (see first picture below) are orange in colour. The first immature motile stage, known as a crawler (the image below shows the flat orange larva in alcohol), is also orange with legs and black eyes. The subsequent instars are sessile, and resemble the adult.

 

The stage used for identification purposes is the first instar larva of the sistens morph (the neosistens stage). The spinal and pleural sclerites of mesothorax, metathorax and abdominal tergites 1-5 are not fused. The pleural sclerites of Adelges piceae are without wax glands. The spinal sclerites have well-developed wax pore plates along the inner margins. The wax pore plates on the inner margins of meso- and metathoracic spinal sclerites are divided into 3-4 angular, or rounded, areas. Central areas of wax pore plates on meso- and metathoracic spinal sclerites often more-or-less triangular, each with 3-6 pits. The total number of pits on the 10 central areas is usually less than 40 (but this ranges from 18 to 59).

In the U.S.A. Adelges piceae is a serious pest of natural fir forests and to the Christmas fir tree industry. Adelges piceae is invasive outside of its native central Europe, from where it spread via timber imports. Adelges piceae is limited in its northern distribution by cold weather. The eggs and newly hatched nymphs are spread by wind, on animals, clothing, vehicles and other equipment.

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Acknowledgements

We have made provisional 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).

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