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Waxy grey pine needle aphidOn this page: Identification & Distribution Biology & Ecology Life cycle Interspecific competition/association Defensive behaviour Natural enemies Other aphids on the same host Damage & Control
Identification & Distribution:
Schizolachnus pineti apterae (see first picture below), are dark greyish-green or occasionally brownish, and are usually covered in wax meal giving a light bluish-grey appearance (cf. Schizolachnus obscurus which is usually brown and wax-covered). Note that the individual pictured has only recently moulted to become an adult, so only has a partial wax cover. 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:
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
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.
The bum-waggle initiates synchronised bum-waggling by many of the aphids as can be seen in the video below.
video copyright Alan Watson Featherstone, all rights reserved.
This synchronised behaviour may give the appearance of a much larger organism that would scare of potential predators.
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.
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.
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.