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Identification & Distribution:

The apterae are dark greyish-green covered in wax meal giving a light bluish-grey appearance. The last rostral segment (R5) is very short and stumpy with a short tip. R5 is less than 46 um long from base to tip, and less than 0.45 times R4. The hind tibiae are pale or dark and very densely hairy. The body length is 1.2-2.5 mm.

They are found on numerous species of Pines (Pinus spp.), especially on young Pinus sylvestris, forming dense colonies in rows along the previous year's needles. Oviparae and alate males occur in October-December, but in years with mild winters colonies may persist through to the next year. Schizolachnus pineti is common and widespread in Europe and parts of Asia and introduced to North America.

 

The first image above shows two adult apterous Schizolachnus pineti (one just recently moulted so with little wax coating) and nymphs. The second image shows an alate grey waxy pine needle aphid about to take off. It is not always easy in photos to distinguish between Schizolachnus pineti and Schizolachnus obscurus.  The colour is diagnostic (grey-green for pineti, brown for obscurus), but sometimes hard to assess given the waxy coating. Host is only a partial clue because although Schizolachnus obscurus is not known to occur on Scots Pine, Schizolachnus pineti may occur on Corsican Pine.

The image below shows what is apparently a mixed species colony in East Sussex with both Schizolachnus pineti and Schizolachnus obscurus living together on a garden Pinus.

Previously on this website we debated whether the brown aphids were simply S. pineti that have moulted more recently, or were a different colour form. We have now concluded that they are indeed Schizolachnus obscurus and that this is a genuine mixed species colony. Whether the host was Scots Pine is another matter - it certainly appeared to be, but unfortunately we cannot be certain.

 

Biology & Ecology:

Apterae of Schizolachnus pineti can be found on pines all year round providing the winter is not too severe. The picture below shows a thriving colony on Scots pine (Pinus sylvestris) in UK in February when few other species of aphids are around.

Waxy pine needle aphids show what is called contact clustered aggregation in which the bodies of individuals are in mutual contact in rows along the pine needles. The aphids use touch to communicate the presence of a predator, there being no evidence for an alarm pheromone (Kidd, 1982 ). An interesting feature of this behaviour first described by Völkl & Stadler (1996)  can be seen below. The aphids feeding at each end of the colony face towards the centre of the colony, and cover the full width of the needle with their legs.

This is apparently defensive behaviour against specialized predators such as the parasitoid Pauesia, the coccinellid Scymnus nigrinus (Vohland, 1996 ) and the syrphid Didea intermedia (Evenhuis, 1978 ). Also note the different appearance of the 'end' aphids - they appear to have much less wax. The reason for this is unclear - perhaps they can be more agile as a result, or maybe they are 'sacrificial cows'. There is also an accompanying (green) Eulachnus agilis  (at extreme right) which had been feeding on the other side of the needle.

The response of the 'guard' aphids to contact with a predator or other disturbance is is best described as a 'bum waggle'. Both the fore and hind pairs of legs are spread out, and the backside of the aphid is vigorously jerked into the air as can be seen in the pictures below.

 

Similar defensive behaviour has been described in several other aphid species (Dill et al. (1990) ; Hartbauer (2010) ). The only predator we have so far observed taking Schizolachnus pineti is shown below - an unidentified species of predatory mite.

Note the yellow liquid coming from the siphunculi. This would normally indicate release of an alarm pheromone. There is a small amount of secretion from the left hand siphunculus of the closest aphid, but there was no evidence of any response from the other aphids on the needle, supporting the suggestion that Schizolachnus pineti does not produce an alarm pheromone.

We have seen other potential predators on infested trees including the Pine ladybird (Exochomus quadripustulatus) shown below, but whether it takes waxy pine needle aphid is unclear.

Exochomus quadripustulatus (Pine Ladybird) on Pinus sylvestris (Scots Pine) infested with Schizolachnus pineti (Grey waxy pine needle aphid) at Ashdown Forest, East Sussex, UK on 14/8/10 at 13.33 h.  

Parasitoids frequently attack Schizolachnus pineti, and the second picture above shows mummies of this species most likely parasitized by a Pauesia species.

 

Other aphids on same host:

Blackman & Eastop list about 170 species of aphids  as feeding on pines worldwide, and provides formal identification keys for aphids on Pinus. Of the 30 species on Scots pine (Pinus sylvestris) Baker (2015)  lists 15 as occurring in Britain: Cinara brauni,  Cinara nuda, Cinara pilosa, Cinara pinea,  Cinara pini,  Cinara pinihabitans, Essigella californica,  Eulachnus agilis,  Eulachnus brevipilosus,  Eulachnus rileyi,  Pineus orientalis, Pineus pini,  Pineus strobi, Prociphilus pini, and Schizolachnus pineti.

 

Damage and control

Heavy infestations often occur and may damage plantation trees. However, control is seldom economically justified. Holopainen & Kainulainen (2004)  have assessed the impact of future global warming on the performance of the aphid Schizolachnus pineti and on the nutritional quality of Pinus sylvestris. Fecundity had a curvilinear response, with an optimum at 24 or 26 C, which is 4 to 6 C above the current mean daytime temperatures in Finland. Hence warming is likely to increase problems with this species.

Identifications & Acknowledgements

Whilst we try to ensure that identifications are correct, we do not warranty their accuracy. 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

  •  Dill, L.M. et al. (1990). The economics of escape behaviour in the pea aphid, Acyrthosiphon pisum. Oecologia 83, 473-478. Full text 

  •  Evenhuis, N.L. (1978). Didea intermedia (Diptera, Syrphidae) as a predator of Schizolachnus pineti (Hemiptera, Aphididae) and prey specialisation in other aphidophagous syrphid larvae. [in Dutch] Entomologische Berichten, Amsterdam 38, 129-131.

  •  Hartbauer, M. (2010). Collective defense of Aphis nerii and Uroleucon hypochoeridis (Homoptera, Aphididae) against natural enemies. PLoS ONE 5(4), e10417. Full text 

  •  Holopainen, J.K. & Kainulainen, P. (2004) Reproductive capacity of the grey pine aphid and allocation response of Scots pine seedlings across temperature gradients: a test of hypotheses predicting outcomes of global warming. Canadian Journal of Forest Research 34 (1), 94-102.  Abstract 

  •  Kidd, N.A.C. (1982). Predator avoidance as a result of aggregation in the Grey Pine Aphid, Schizolachnus pineti. Journal of Animal Ecology 51 (2), 397-412. Abstract 

  •  Vohland, K. (1996). The influence of plant structure on searching behaviour in the ladybird Scymnus nigrinus (Coleoptera: Coccinellidae. European Journal of Entomology 93, 151-160. Full text 

  •  Völkl, W. & Stadler, B. (1996). Colony orientation and successful defence behaviour in the conifer aphid, Schizolachnus pineti. Entomologia Experimentalis et Applicata 78 (2), 197-200. Abstract