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Identification & Distribution

Adult apterae of Cinara strobi are long-bodied aphids with a body colour of shiny metallic to dull grey black. They have a brown head, a spinal stripe of white wax on the thoracic tergites and on the posterior abdominal tergites, and (usually) 2-3 white wax spots on each side of the dorsum. The femora are yellow-brown basally, but darker towards the apices. The hind tibiae are wholly dark and markedly bowed (see pictures below) (cf. Cinara atlantica and Cinara pinea which both have a pale section on the basal half of the hind tibiae). The longest hairs on the dorsal side of the hind tibia are usually less than 1.5 times the width of the hind tibia at midpoint (cf. Cinara pergandei which has those hairs usually more than 1.5 times the width of the hind tibia). The siphuncular cones are black. The body length of adult apterae is 3.0-3.4 mm. Immature Cinara strobi are pinkish-brown with two longitudinal faint greyish-green dorsal stripes.

Both images above by permission, copyright Claude Pilon, all rights reserved.

Alate Cinara strobi (see second picture above) are also grey black with white wax markings.

Cinara strobi is mainly found on the branches and upper trunk of eastern white pine (Pinus strobus), although there are also records from Canadian red pine (Pinus resinosa). The aphids occur in comparatively large loose colonies and are usually attended by numerous ants. In autumn sexuales are produced and overwintering eggs are laid on the needles. The distribution of Cinara strobi follows that of its host, eastern white pine, from Newfoundland to Ontario in Canada and south to North Carolina in the USA.

 

Biology & Ecology

The overwintering eggs of Cinara strobi hatch in spring. Immatures of the species have pinkish brown cryptic coloration which matches with the bark colour of eastern white pine (see picture below).

Image above by permission, copyright Claude Pilon, all rights reserved.

When they reach the adult stage they instead have aposematic coloration (see picture below) - a conspicuous black and white pattern used by many organisms to signal to potential predators that the anticipated prey is distasteful or dangerous.

Image above by permission, copyright Claude Pilon, all rights reserved.

This does not of course necessarily mean that Cinara strobi is distasteful to predators - it may instead be a Batesian mimic (which is itself harmless but resembles a toxic insect). Cinara strobi does not rely solely on its aposematic coloration to protect it from predators, but has two other defense behaviours.

Bradley (1951) noted that when disturbed these aphids quickly raise their bodies at an oblique angle to the surface of the tree, so that only the front legs and the mouthparts maintain contact with the bark. This was thought to be aimed at placing the vulnerable abdomen beyond the reach of predators that move about close to the surface of the bark. The body is moved rapidly from side to side while in this position, which may further serve to discourage attack by a predator.

Cinara strobi are also attended by numerous ants. Ant species recorded as attending this species include Crematogaster lineolata, Formica aserva (formerly known as Formica subnuda) and Lasius alienus (Bradley, 1961 ). Some ant species, especially Crematogaster and Formica species, are known to defend the aphids they tend by attacking any intruding predator.

Both images copyright E. Bradford Walker under a Creative Commons Attribution 3.0 License.

In autumn sexuale forms are produced. The winged males mate with the oviparous females which in this species do not have a pericaudal wax ring. The mated oviparae then lay the eggs in rows along the needles of small twigs at the branch ends. The eggs are attached to one another at their ends and to the surface of the needle. Just after laying the eggs are orange in colour, but they soon darken to shiny black (see picture below).

Image copyright Beatriz Moisset under a Creative Commons Attribution-Share Alike 4.0 International license.

 

Other aphids on the same host

Cinara strobi has been recorded on two species of pine, eastern white pine (Pinus strobus) and Canadian red pine (Pinus resinosa).

Blackman & Eastop list 18 aphid species of aphid as feeding on Pinus strobus worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 5 as occurring in Britain (Show British list).

 

Damage and control

Feeding by large colonies of Cinara strobi can cause branch dieback and discoloured needles. Small trees may be killed by the aphid. Heavy infestations produce large quantities of honeydew which results in sooty mould fungi and reduced photosynthesis.

Chemical control is rarely necessary. For heavy infestations horticultural oil can be used to kill the eggs.

Acknowledgements

We are especially grateful to Claude Pilon for pictures of Cinara fornacula (for more of his excellent pictures see, and).

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).

Useful weblinks

References

  • Bradley, G.A. (1951). A Field Key to the Species of Cinara (Homoptera: Aphididae) of Canada East of the Rockies. Canadian Entomologist 83(12), 333-335. Abstract

  • Bradley, G.A. (1961). A study of the systematics and biology of aphids of the genus Cinara in Canada. PhD thesis, McGill University, Montreal, Canada. Full text