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Identification & Distribution:

Schizolachnus pineti apterae (see first picture below) are dark greyish-green or occasionally brownish, and are covered in wax meal giving a light bluish-grey appearance (cf. Schizolachnus obscurus which is usually brown and wax-covered). The fourth rostral segment (RIV) is 2.3-3.7 times the length of the fifth rostral segment (RV) (cf. Schizolachnus obscurus in which RIV is 1.6-2.1 times the length of RV). RV is short and stumpy and is 33-43 μm long (cf . Schizolachnus obscurus in which RV has an extended tip and is 43-60 μm long). The hind tibiae are pale or dark and very densely hairy. The body length is 1.2-2.5 mm.

Schizolachnus pineti alate (see second picture above) is similarly covered in dense grey wax meal.

Schizolachnus pineti can be found on numerous species of Pines (Pinus species), but especially on young Scots pine (Pinus sylvestris) where it forms 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.

 

Biology & Ecology:

Life cycle

Fundatrices of Schizolachnus pineti have been found in Britain in May, and oviparae and alate males in October-December, but we have yet to find them. Most years we have been able to find viviparae of Schizolachnus pineti on Scots pine throughout the winter months. The picture below shows a thriving colony with all immature stages present on Scots pine (Pinus sylvestris) in southern England in February when few other species of aphids are around.

Interspecific competition / association

Eulachnus agilis associate in the field with a species of aphid that forms colonies, the wax-coated Schizolachnus pineti. When occurring alone, Eulachnus agilis favours old senescing needles, whilst Schizolachnus pineti avoids them. Despite this, Kidd et al. (1985) showed that both species show a significant tendency to share shoots and needles in the field.

We give more information on this association in Eulachnus agilis

Defensive behaviour
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)).

Natural enemies
We have found Anystis mites predating grey waxy pine needle aphids Schizolachnus pineti (see picture below). Grobler 1962 found that Anystis agilis was an important predator of Schizolachnus pini-radiatae in Canada, causing a 30-50% mortality among overwintering eggs. For more information on mites parasitizing and predating aphids see Mites parasitizing & predating aphids.

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.

 

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 make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made 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

  • Kidd, N.A.C. et al. (1985). An association between two species of pine aphid, Schizolachnus pineti and Eulachnus agilis. Ecological Entomology 10(4), 427-432. 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