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Spruce shoot aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Apterae of Cinara pilicornis come in two colour forms. The commonest form is a plain orange brown (shown below first), but some are a greyish green. The whole aphid is clothed with numerous fine hairs and is more or less covered with a dense mealy secretion. The legs are yellowish but the distal half of the hind femur is darker. The hind tibiae are pale, or at least paler basally and medially than at apex. Most of hairs on the outer side of the middle section of the hind tibia exceed 0.12 mm in length (this character distinguishes Cinara pilicornis from Cinara piceicola and Cinara hottesi ). The second hind tarsal segment is sickle shaped and longer than the maximum diameter of the siphuncular cones (this character distinguishes Cinara pilicornis from Cinara costata and Cinara pruinosa ). The siphunculi are small and pale brownish. Their body length is 2.1-4.7 mm.
First image copyright Sandy Rae, all rights reserved.
The spruce shoot aphid may be found on many different spruce species including Norwegian spruce (Picea abies) and Sitka spruce (Picea sitchensis). It may also colonise western hemlock (Tsuga heterophylla). Cinara pilicornis is found throughout Europe through to China and Japan and it has been introduced to Australia, New Zealand, North and South America.
Biology & Ecology:
Cinara pilicornis lays its eggs in autumn on current year needles. The eggs begin hatching early the next March before bud burst. Initially small colonies develop on undersides of the previous year's twigs, but these move on to new growth after bud-burst as shown below. The nymphs are very cryptic and can be difficult to spot amongst the young needles.
By the second and third instar the mealy covering becomes more apparent (see picture below). The species is usually not ant attended.
The young aphids develop into apterous fundatrices (see first picture below) which are larger and somewhat darker than their eventual offspring.
There are then a series of parthenogenetic generations with both wingless and winged viviparae with two colour forms - orange brown or greyish green. An apterous adult of the orange-brown form is pictured below, together with an immature of the green form.
Image copyright Sandy Rae, all rights reserved
The proportion of winged viviparae is higher than in any other Cinara species. Numerous alatae are produced in May-July. Oviparae and males are produced in early August-November.
In Britain Carter & Maslen (1982) report that in some years it is extremely abundant among young spruce plantations. They also comment that it was far less common in the 1950s and 1960s than it was in the 1980's. Our own impression is that it is now less common than at the time Carter & Maslen were writing, possibly because of a decline in the planting of spruce.
Parry (1979) looked at factors affecting the low temperature survival of the eggs on Sitka spruce. Glycerol and mannitol were present in the eggs but neither appeared to be related to their supercooling ability which was related to the temperature in the period preceding collection.
Various predators have been recorded attacking the spruce shoot aphid. Kula (1982) found the larvae of fifteen different species of Syrphidae in colonies of Cinara pilicornis). The most abundant species was Episyrphus balteatus, the adult of which is pictured below.
The spruce shoot aphid has been found to be common in polluted areas. Holopainen (1991) looked at the effect of high levels of pollution on the spruce shoot aphid. Under experimental conditions aphid populations were found to be higher on seedlings exposed to pollutants (gaseous sulphur dioxide, sodium fluoride, calcium nitrate and ammonium sulphate) than on those not exposed. Fluoride had a stronger positive effect on aphid numbers than sulphur dioxide or nitrogen.
Stadler (1997) studied the egg distribution and survival of Cinara pilicornis on damaged and undamaged Norway spruce (Picea abies). Host trees showing either heavy symptoms of needle-yellowing or looking green and healthy were compared. Host plant quality did not seem to influence the proportion of eggs surviving to spring. Also, the biomass of developing first instar larvae of the fundatrices was independent of the degree of needle-yellowing. Damaged or stressed trees did not seem to be better hosts for Cinara pilicornis.
Damage and control
Cinara pilicornis provides an important source of honeydew for bee populations. Hence bee keepers view this aphid very favourably, although it can damage young trees. Moulds growing on honey dew may stain shoots black. There is some evidence that the aphid can cause the current year's needles to turn yellow and fall from the lower side of the shoots that have supported colonies.