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Identification & Distribution:

Tuberolachnus salignus are very large aphids with a body length of 5.0-5.8 mm. Apterae are mid-brown to dark brown with several rows of black sclerotic patches. The body is covered with numerous fine hairs, which give a greyish-golden sheen to the abdomen. There is a large dark brown tubercle in the centre of the back, just in front of the siphunculi which are on large dark cones. The antennae are less than half the body length. Alates have the forewing membrane unpigmented but the pterostigma and costal margin are dark brown.

The giant willow aphid lives on the stems and branches of numerous willows & sallows (Salix spp.) and is also very occasionally recorded from poplar (Populus). Its distribution is almost cosmopolitan wherever willows are grown.

 

The first image shows several apterae in the midst of a large colony on a young branch of white willow (Salix alba). Note the back of each aphid bears a large dark brown tubercle, the function of which is unknown (Heie, 2009 ). The second image shows an alate Tuberolachnus salignus - it also has the characteristic dorsal tubercle. Unlike Lachnus aphids  (to which it is closely related), the forewing membrane is unpigmented.  

Biology & Ecology:

Tuberolachnus salignus is anholocyclic and no males have ever been found, so all reproduction is parthenogenetic. The females produce live young which are all genetically identical (clones). The species is strongly aggregative and can build up to very large colonies in late summer. Density is the main factor affecting whether a nymph develops into an aptera or alate, although temperature may also have an effect.

Hargreaves & Llewellyn (1978)  showed that the degree of crowding also affects the number of young produced. The number of young nymphs produced reaches a maximum at moderate degrees of crowding, but declined in both uncrowded and densely crowded situations. Collins (2001)  notes the colonies can cover much of the 1-3 year old stem surface of a tree. Much like Lachnus  species, they wave their hind legs in the air if disturbed by a predator. This behaviour may be synchronised over large areas of the colony. Large Tuberolachnus salignus colonies attract numerous honeydew-feeding insects.

 

Colonies of nymphs with the founding alate(s) are usually ant attended. The two images above show jet black ants (Lasius fuliginosus) attending such colonies on white willow, the first record as far as we know of this ant species attending Tuberolachnus.

 

Southern wood ants (Formica rufa) also attend (and vigorously defend) colonies of nymphs with the founding alate. These pictures show ant-attended Tuberolachnus salignus colonies on sallow (Salix cinerea) rather than Willow. The alate has an unusually long postreproductive life (Collins & Leather, 2001 ) and remains with her nymphs long after they have been born. Dixon & Wratten (1971)  have suggested that aggregative aphids benefit their clonal siblings by improving the nutritional qualities of the host through the 'sink effect' which may explain the long post-reproductive life of Tuberolachnus.

The image below shows several southern wood ants tending a large colony of giant willow aphid on Sallow in October.

Despite the presence of large quantities of honeydew, colonies are not always ant attended. Collins (2011)  reports that the aphids may actively repel ants. Many years ago, Buckton (1876)  recorded the behaviour of aphids if there were no aphids to remove honeydew droplets. He reports that "if [the droplet] is not quickly withdrawn by an attendant ant ... it is projected by a peculiar jerk to a considerable distance". This ejected honeydew then attracts a different group of honeydew feeders.

 

These two images show social wasps gleaning (collecting) the aphid honeydew from leaves beneath a Tuberolachnus salignus colony. Unlike ants they do not collect the honeydew directly from the aphids. However, there is some evidence that they deter predators (Letourneau & Choe, 1978 ), which would make this a mutually beneficial relationship, much as that between ants and aphids. Certainly the swarm of wasps around some colonies would dissuade many mammals from approaching.

No parasitoid of the species has been recorded in Europe. In Japan, Tuberolachnus salignus is parasitized by the braconid Aphidius salignae and by a specific hyperparasitoid Pauesia salignae, which might indicate that this is where it is endemic. Predators of this species are rarely recorded, not suprisingly because they appear to have aposematic colouration, perhaps to indicate they are distasteful. Hence our interest in the photograph below. Our thanks to Dr Wagner for submitting this.

Guest image, Copyright Dr Wagner, all rights reserved

This is not the first report of Harlequin ladybirds predating giant willow aphids (see also Keith Edkins ) so it seems likely that this predator at least finds this species palatable.

Then there is the 'Giant Willow Aphid Mystery'. Tuberolachnus aphids have only been found on willow trees from July through to early March. Numbers tend to peak in October, but by February few are left on the trees and none has been seen from April to July. They are said to be very active in January and February when they often walk around off the host. (Natural History Museum, 2011 ). Perhaps they go into diapause in spring, living in bark crevices before re-emerging in July to feed on willow.  

Damage and control

Collins et al. (2001a)  demonstrated that Tuberolachnus salignus markedly reduced the above and below ground growth of willow trees both during and after infestation. Infestations also reduced the survival of infested trees. This is serious problem where willow is being grown for fuel, and also for ornamental willow varieties.

The most viable control strategy is to select willow varieties for pest resistance. Collins et al. (2001b)  showed that reproduction rates of T. salignus differ between willow varieties and species. Aradottir (2009)  has since demonstrated host preferences by olfactometry studies. These results were supported by subsequent field studies.

Acknowledgements

We would like to specially thank Dr Wagner for the photo of Tuberolachnus salignus (Giant Willow Aphid) on Salix being predated by Harmonia axyridis  (Harlequin Ladybird) in Gelnhausen, near Frankfurt on Main, Germany.

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

  •  Aradottir, G. et al. (2009) Host selection of the giant willow aphid, (Tuberolachnus salignus). Redia, 92, 223-225.  Full text 

  •  Buckton, G.B. (1876) British Aphides. Vol. III. The Ray Society, London.  Full text 

  •  Collins, C.M. (2001). Willow Aphids on SRC Willow. Effects of aphids on host plants: A project summary. In: Short Rotation Coppice - Breeding, Pest and Disease Control. DTI, Blagdon, Somerset.  Full text 

  •  Collins, C.M. (2011). Research Interests: Aspects of the ecology of willow aphids.  Full text 

  •  Collins, C.M. & Leather, S.L. (2001). Effect of temperature on fecundity and development of the Giant Willow Aphid, Tuberolachnus salignus (Sternorrhyncha: Aphididae). European Journal of Entomology 98 (2), 177-182.  Full text 

  •  Collins, C.M. et al. (2001a). The impact of the aphids Tuberolachnus salignus and Pterocomma salignus on willow trees. Annals of Applied Biology 138 (2), 133-140. Abstract 

  •  Collins, C.M. et al. (2001b) Host selection and performance of the giant willow aphid, Tuberolachnus salignus Gmelin - implications for pest management. Agricultural and Forest Entomology, 3, 183-189. Abstract 

  •  Dixon, A.F.G. & Wratten, S.D. (1971). Laboratory studies on aggregation, size and fecundity in the black bean aphid, Aphis fabae Scop. Bulletin of Entomological Research, 61, 97-111. Abstract 

  •  Hargreaves, C.E.M. & Llewellyn, M. (1978). The ecological energetics of the Willow Aphid Tuberolachnus salignus: The influence of aphid aggregations. Journal of Animal Ecology 47 (2), 605-613.  Abstract 

  •  Heie, O.E. (2009). Aphid mysteries not yet solved/Hemiptera:Aphidomorpha. Monograph: Aphids and other hemipterous insects 15, 31-48.  Full text 

  •  Letourneau, D.K. & Choe, J.C. (1978). Homopteran attendance by wasps and ants: The stochastic nature of interactions. Psyche 94, 81-91.  Abstract  Full text 

  •  Natural History Museum (2011) Large Willow Aphid.  Full text 

 

Identification requests

Michele Smith 30 Mar 2015; Willow aphids

I found your site trying to identify and control a large aphid colony on my willow tree.
They have been coming around for about 4-5 years now and I am getting worried they are going to kill my willow.
I live in Australia, in the northern part of NSW at around 700m where it gets cool in winter.
They seem to start at the beginning of summer and I think die out heading into winter.
I also find them congregating on a wooden bench underneath the willow.
I desperately want to control these pests as they leave a sticky mess under the tree which coats everything.
The tree is at my back door and is my pride and joy and I am starting to panic that they will kill it.

I cannot identify which aphid it is so I have included some photos for your interest including some predators.
There are other insects living amongst them which I have also included in case they are of interest.
They are a brown color with three horn like structures on their bum.
They come in all sizes and can get quite large.
There are no ants.
They seem to eject their 'piss' which falls like rain and coats everything underneath.
This sticky mess coats the leaves underneath and seems to be creating a mossy mould or fungus on the branches.
There are winged ones and non winged ones.
I'm not sure which species willow it is but it seems to me to be a regular weeping willow.

I crush what I can reach almost daily in an attempt to control them, but they are always back in numbers by the next day so my attempts seem futile.
Can you please offer any help as to how I can control them?
I am organic and have even considered spraying them with pesticide!

It is just a regular willow to my knowledge. Below is a Willow aphid. They come in various sizes, as do their colonies.

     

Images copyright Michele Smith, all rights reserved.

This is one having a baby. There are winged ones as well.

 

Images copyright Michele Smith, all rights reserved.

This is a lady beetle larva eating an aphid. Notice the mess on the leaves, this one is actually not bad. Mossy growth on branches can get much thicker than this. These beetles are also around.

     

Images copyright Michele Smith, all rights reserved.

Bob, Influentialpoints:

  • Your horned monsters are giant willow aphids Tuberolachnus salignus. They live on the stems and branches of many willow species. These aphids occur almost anywhere that willows are grown. But, although they are not the most common willow aphids they are among the more commonly noticed - at least by humans. When seen individually they look very striking, but en masse they are less visible to predators - most especially birds.

    Giant willow aphids tend to prefer trees with old and broken branches, and other crevices, where they can hide from predators earlier in the year.That said, whilst these aphids may reduce tree growth, they seldom kill it.

    The interesting thing is that your aphid species appears to have only recently arrived in Australia, but we suspect that the aphid is probably now well established there.

    Tuberolachnus salignus was first recorded in New Zealand in 2014, and was found to already be widepread in the country. It was then surmised that the species had spread from Australia, albeit it had not at that time been reported from Australia. It has been reported from Tasmania.

    About the only sure way to get rid of these beasties is to remove the tree - which I assume you don't want to do. Insecticide treatment is relatively ineffective and expensive - and they will probably return. Classical 'biological control' of aphids (release of natural enemies) is usually only worthwhile in greenhouses. In a 'natural situation', aphid numbers are usually kept in check by predators and parasites, such as the ones you photographed - which is partly why infestations tend to burn themselves out.

    One way you, yourself, might reduce the problem is to encourage insectivorous birds - such as by placing feeders where the aphids aggregate. Note, since birds can take awhile to find new sources of food, you may have to put them out ahead of time. Or, if you are in a dry area, water may be nearly as attractive.

    If all else fails, you could simply accept you are host to a remarkable piece of natural biology - and invite your local naturalists round to partake of your spectacle. Our next-door neighbors had many amazing dinner parties showing off their nightly visiting wild badger - up-close and personal! You already have some fascinating predators feeding on the colony. The yellow beetle is the Netty Ladybird Beetle (Harmonia testudinaria).

Thank you for your very informative response.
I will be sure to check out all the links you have referred me to.

Thank you for identifying my lady beetle too :)

Although I am a bit upset that I may not ever be able to remove these pests I am surely going to give it a go.
Yesterday we sprayed the tree with a mix of Eco-oil and Neem oil.
It seems to have quietened the place down a bit at least for the moment? although I still had my usual crushing session.
I plan to repeat this application if successful to try keep numbers down and will also concentrate on the knobbly lower bark (thanks to your email).
I will let you know if I have success.

Bob, Influentialpoints:

Thanks for the link.
It's good to get a different take on the subject and have a bit of compassion for the poor old aphid. After all, they may kill a few trees here and there, we on the other hand are wiping out forests by the truckload daily, who are we to criticise?

I was just remembering that what made us notice the aphids (about 4-5 years ago), apart from the sticky mess that coated everything, was that the bees were in the tree humming away. At first we thought the tree was re-flowering or something? (its hard to tell with the weird climate these days) but I think they are after the honeydew?

Also, about 10 years ago we got chooks, before that we had large populations of lady beetles and their lava, they covered the yard especially under the willow. Maybe the aphid was here all along and the lady beetle was keeping them in check?

Being organic we always try not to use poisons or chemicals of any sort either in the house or out. We are using eco-oil out of desperation, but it is not supposed to hurt lady beetle, bees, earthworms or lacewings so should be alright.
Neem oil is also a good one that targets aphids and is okay for organics, not to sure about the bees though. We do not want to hurt anybody unintentionally, I would just like to control the numbers a bit I suppose.

Thanks again for all your help.

This is my beautiful willow.

Image copyright Michele Smith, all rights reserved.

Bob, Influentialpoints:

  • Don't know if this is of interest but, purely by chance, we have just finished writing something about the upsides and downsides of some of the invasive aphids in Europe.