Tag Archives: Picea abies

A Christmas Aphid

A few weeks ago I was contacted by a researcher from the One Show.  They were interested in the possibility of doing a festive piece about what people bring into the house with them on Christmas trees with the idea that George McGavin would shake a Christmas tree over a piece of white paper and tell the audience all about the insects that fell out;  a typical media “how gross nature” is piece.

The researcher was somewhat disappointed when I told her that being winter  that there would be relatively little hiding in the tree, especially if it was a commercially reared cut tree bought from a garden centre or other retail outlet.  Cut Christmas trees in the UK tend to be harvested from October onwards so the chances are that your tree has lain about for at least a month before you bring it into your house and by that time, any sensible winter active herbivore has long departed for fresher trees.  Although conifer trees have a large number of insect species associated with them, most of them spend the winter either off the tree or as inactive eggs hidden under the bark or as eggs actually laid inside the needles e.g. the pine sawfly Neodiprion sertifer.  You would probably find a few opportunistic spiders and possibly some mites and bark lice, but not much else unless you had a potted tree or one that had only recently been felled.  The other thing that would influence what you would find is of course what species of tree you had bought.  Gone are the days when the Christmas tree and Norway spruce (Picea abies) were one and the same.  I guess my caveating and pessimistic reply proved too much for the researcher as I never heard back from her.

The one insect I had waxed lyrical about was of course an aphid, the green spruce aphid, Elatobium abietinum to be precise.   There are a number of aphid species that make a living on spruce trees, some of them quite large and spectacular such as the greater black spruce aphid, Cinara piceae, but like most aphids, they overwinter as eggs (Leather, 1992).

Cinara_piceae_aptera_on_Picea_abies_at_Selwyn_Wood

The greater black spruce aphid, Cinara piceae (Photograph courtesy of http://influentialpoints.com/Gallery/Aphids_on_spruce_Picea_in_Britain.htm)

The green spruce aphid, E. abietinum or Elatobium as it is commonly known, (there is only one species in the genus), overwinters in the UK and most other parts of the world, as an adult or immature stage (nymph) (Nicol et al., 1998).

The adult is small, green and inconspicuous, and quite difficult to see unless you are actually looking for them.

Elatobium and nymphs

The green spruce aphid, Elatobium abietinum and nymphs.

The green spruce aphid is a native of Europe and normally attacks Norway spruce.  They avoid current year needles as these tend to be distasteful to them (the chemistry of young spruce needles is pretty nasty and makes them unsuitable hosts for the aphids) and feed on the previous year and older needles.  Spruce needles, even older ones, are not particularly nutritious, so the aphid injects a toxic material in its saliva that makes the needles more nutritious by encouraging nitrogen mobilisation (Kloft & Erhardt, 1959).  Their populations build up during the spring and towards the end of May and beginning of June, they take flight and the trees seem relatively free of aphids (Bevan, 1966).  As they are so small, they are most obvious after they have gone, either by the damage they cause, premature senescence of the needles as shown in the photograph above, premature needle drop or by the presence of a large number of ladybird larvae.  When I worked for the Forestry Commission as an entomologist, I quite often received phone calls from distressed foresters who had sprayed the blue beetles damaging their spruce trees!

Although they are difficult to find during the summer months they are still there; this summer collapse of singe-host aphids is quite common (Karley et al., 2004).  In the autumn,  Elatobium populations begin to build up and as they do not overwinter as eggs, they are able to continue reproducing through the winter months (Powell & Parry, 1976). Sitka spruce, Picea sitchensis, the most commonly grown conifer in the UK, is a native of North America and as such has very low resistance to Elatobium and displays an almost hypersensitive response to the toxic saliva produced by the aphid.

If it is a particularly mild winter then the spruce trees are likely to show severe signs of damage by June and July.  After several mild winters spruce trees may end up with only current year needles present, which has a severe effect on their growth and appearance.

Elatobium damage needles

Branches of Sitka spruce with only current year needles present after a severe Elatobium abietinum infestation

Elatobium damage trees

Sitka spruce trees showing discoloured needles after attack by Elatobium abietinum.

It may be small, inconspicuous and not worth a TV appearance, but  Elatobium abietinum is now a pest with a world-wide distribution and an international reputation.

References

Bevan, D. (1966). The green spruce aphis Elatobium (Neomyzaphis) abietinum Walker. Scottish Forestry 20, 193-201.

Karley, A. J., Parker, W. E., Pitchford, J. W. &Douglas, A. E. (2004). The mid-season crash in aphid populations: why and how does it occur? Ecological  Entomology 29, 383-388.

Kloft, W. & Ehrhardt, P. (1959). Unterschungen uber Saugtatigkeit und Schadwirkung der Sitkafichtenlaus, Liosomuphis abietina (Walk.), (Neomyzaphis abietina Walk.).  Phytopathologie Zeitzschrqt 35, 401 – 410.

Leather, S. R. (1992). Aspects of aphid overwintering (Homoptera: Aphidinea: Aphididae). Entomologia Generalis 17, 101-113.

Nicol, D., Armstrong, K. F., Wratten, S. D., Walsh, P. J., Straw, N., Cameron, C. M., Lahmann, C. & Frampton, C. M. (1998). Genetic diversity of an introduced pest, the green spruce aphid Elatobium abietinum (Hemiptera: Aphididae) in New Zealand and the United Kingdom. Bulletin of Entomological Research 88, 537-543.

Powell, W. & Parry, W. H. (1976). Effects of temperature on overwintering populations of the green spruce aphid, Elatobium abietinum.  Annals of Applied Biology 82, 209-219.

Sullivan, C.R. (1965) Laboratory and field investigations on the ability of eggs of the European Pine Sawfly, Neodiprion sertifer (Geoffroy) to withstand low winter temperatures.  Canadian Entomologist, 97, 978-993

 

Postscript

During the 1980s when ‘Acid Rain’ was very much in the news, Elatobium damage was often mistaken as a symptom of acid rain in the UK.

 

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Not all aphids live on leaves

I haven’t written about aphids for a while, so I thought I would indulge myself and tell you about a few of my favourite aphids.  Most people’s perceptions of aphids (assuming that they know what  aphids are of course) is that they live on leaves.  They will I think, also possibly know that they are usually found on the undersides of leaves, although I may be assuming too much here.  In fact, many species of aphid do not live on leaves; a number of species feed on shoots, twigs and branches and some actually feed on the main trunks of trees.  Yet other species live on the roots of trees and herbaceous plants, such as the apple-grass aphid, Rhopalosiphum insertum which can be a pest of apples and cereals, feeding on the leaves and buds of apples and the roots of grasses and cereals.   Another root-feeding aphid that is a double pest, is Pachypappa tremulae, the spruce root aphid, which host alternates between the aerial parts of aspen trees and the roots of Norway spruce; easily visible when infesting the roots of young potted plants due to the presence of white waxy tufts on its rear end.

Some aphids not only live underground feeding on roots, but are entirely dependent on being farmed by ants e.g.  Tetraneura ulmi, which host-alternates between elm and grass roots, and  Forda formicaria, which host-alternates between Pistachio trees and grass roots.

Forda_formicaria_hirsuta_root_aphid_03-03-13_3

http://www.aphotofauna.com/images/bugs_homoptera/bug_forda_formicaria_hirsuta_root_aphid_03-03-13_3.jpg

Both these aphids are looked after or ‘farmed’ by the yellow meadow ant Lasius flavus in exchange for donations of honeydew.

Lasius%20flavus%202

These two aphid species, along with a number of others, have an enlarged anal plate surrounded by special hairs that form the so-called trophobiotic organ.  This acts as a storage device that allows the aphid to accumulate honeydew ready for the ants to remove.  Those aphids that have a more casual (facultative) relationship with ants, do not have this organ which is the basis of this remarkable mutualism.

Another aphid that is farmed by ants, but in a somewhat different way, is the rather larger rose root aphid, Maculolachnus submacaula, which as its name suggests, feeds on rose roots.  In this case, the ants allow the aphids above ground but only in an ant tunnel, similar to those produced by termites when they are infesting a building.  I have only ever been lucky enough to see this aphid once, some 35 years ago in Norwich when I was doing my PhD and noticed things that looked like termite trails running up the main stem of one of my rose bushes.  On breaking them open, well I am a curious entomologist, I found to my surprise not only ants but large brown aphids.

Maculolachnus submacula nest

http://jardiweb-floralbum.forumsactifs.com/t1797-colonie-de-pucerons

for a better view of the aphid see http://www.afripics.co.za/home/products/product.php?ProductID=1301564582

But of course the really spectacular ones are those that feed on branches of trees such as the giant willow aphid Tuberolachnus salignus (famous for its sharks fin) and those from the genus Stomaphis which feed through the bark of trees such as oak and

Tuberolachnus

sycamore and are possessed of truly enormous mouthparts such as those of Stomaphis aceris which feeds on sycamore

Stomaphis query aceris

This one, despite its enormous mouthparts, is quite difficult to find as it hides underneath the bark, but luckily it is ant attended so if you see ants scurrying around on the bark of sycamore and disappearing underneath loose flaking bits, it is a good bet that if you gently lever off the loose bark you will find yourself in the presence of this weird-looking creature.

The more I learn about aphids the more I find to marvel at.  Aphids really are remarkable and we know so little about so many of them and their weird and wonderful life styles.

Useful References

Blackman, R.L. & Eastop, V.F. (19 94) Aphids on the World’s TreesAn  Identification and Information Guide.  CABI Publishing. http://www.aphidsonworldsplants.info/index.htm

Evenhuis, H.H. (1968)  The natural control of the apple grass aphid,  Rhopalosiphum insertum, with remarks on the control of apple aphids in general in The Netherlands. Netherlands Journal of Plant Pathology, 74, 106-117  http://link.springer.com/article/10.1007/BF02309501#page-1

Farrell, J.A. & Stufkens, M.W. (1989) Flight activity and cereal host relationships of Rhopalosiphum spp. (Homoptera: Aphididae) in Canterbury New Zealand Journal of Journal of Crop and Horticultural Science, 17, 1-7  http://www.tandfonline.com/doi/abs/10.1080/01140671.1989.10428003

Ivens, A.B.F., Kronauer, D.J.C., Pen, I., Weissing, F.J. & Boomsma, J.J. (2012)  Ants farm subterranean aphids mostly in single clone groups – an example of prudent husbandry for carbohydrates and proteins?  BMC Evolutionary Biology, 12:106 http://link.springer.com/article/10.1186%2F1471-2148-12-106

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