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Pineus orientalis

Spruce - pine woolly adelgid

On this page: Identification & Distribution Biology & Ecology Other aphids on the same host Damage & Control

Identification & Distribution

Pineus orientalis fundatrices, and their offspring (future gallicolae), induce terminal galls on the primary host, Caucasian spruce (= Oriental spruce, Picea orientalis, see first picture below). At the base the needles are reddened, broadened and swollen, with the green, protruding needle tips evenly distributed around the gall. The winged gallicolae (see second and fourth pictures below) have a similar distribution of dorsal wax glands and large distinct facets to Pineus pini, but the facets of the marginal wax glands are smaller and more numerous than those of Pineus pini. They are also smaller in diameter than the largest facets on the head. In the forewings, the costal and sub-costal veins form a parallelogram bordering the stigma (see fourth image below). The anal and medial veins are slightly curved towards, and away from the thorax respectively. Antennal segments III and IV are of equal size, and have large primary rhinaria which are about half the length of the segments (see fifth image below). Antennal segment V is longer than III and IV, but the length of the rhinarium on V is less than half the length of the segment. The winged adult gallicolae that emerge from the gall have a body length of 1.5-2.3 mm. (cf. Pineus pini, which is single-host, and the only winged forms are sexuparae with a body length of 1.0-1.2 mm).

When on the secondary host, Pinus sylvestris, the apterae are known as sistens (see third picture above) and cannot be distinguished from Pineus pini - as they are morphologically identical. The adult sexuales (not pictured) produced on Picea orientalis are orange and quite small. Pigmentation of the female cuticle is very weak, with indistinct gland facets on the dorsal surface. The males are slender, with long legs and very long antennal segments III and IV. They lack the dorsal wax gland facets present on the female.

The first micrograph above shows a Pineus orientalis gallicola dorsal in alcohol. The fore-wing veins important to identifying this species are shown in colour; for clarity neither the hind-wing veins nor radial veins bordering the stigma are highlighted, and the subcostal terminology is simplified. (Note: Adelgids lack the Rs vein.) The second micrograph above shows a ventral view of the antenna. The clarified slide mount below is of an adult Pineus orientalis: winged gallicola.

Micrograph of clarified mount by permission of Roger Blackman, copyright AWP all rights reserved.

Pineus orientalis, unlike Pineus pini, goes through the full holocycle and host alternates from Caucasian spruce (Picea orientalis) to Scots pine (Pinus sylvestris). Pineus orientalis fundatrices emerge from eggs on spruce in August, but do not reach the adult stage till April the following year. Feeding of the fundatrix and her offspring on Picea orientalis in May induces a distinctive reddish gall. Winged gallicolae emerge from this gall in June-July and migrate to Pinus sylvestris where they lay eggs. These hatch to give several generations of apterous sistens, and other forms, between August and the following spring - when sexuparae are produced which migrate back to spruce. These sexuparae produce small wingless males and females which mate, and the females lay eggs. Pineus orientalis is found from western Europe across Asia to Japan.

 

Biology & Ecology

Life cycle

The galls produced on Caucasian spruce are very conspicuous, and often occur on the same trees as the globular galls of Adelges nordmannianae. The gall is terminal, 2-3 cm in length, elongate ovoid (=egg-shaped), usually fairly straight and with the needles more or less decumbent and distributed to all sides. Around the base and halfway up the needles is pinkish-red, while the distal half of each needle remains green. The basal halves of the needles are swollen and thickened.

The picture above shows a more-or-less typical ovoid shaped gall. Those below show (first) a rather elongated gall and (second) three terminal ovoid-shaped galls on the same shoot.

At Bedgebury Pinetum we have observed Pineus orientalis gallicolae emerging from galls on Pinus orientalis in late June (see picture below). Carter (1963) reported that winged gallicolae of Pineus orientalis emerged from galls found in Alice Holt Forest in Hampshire in June-July.

The fourth instars (see picture below) do not ecdyse to the adult winged stage until they have emerged from the gall; as a result the gall is left covered with the shed skins after their emergence.

The winged adult gallicolae remain on the gall until their wings have hardened (see picture below), and then migrate to their secondary host.

Carter (1963) compared the suitability of various likely secondary hosts by confining 20 or more recently emerged active gallicolae to new shoots of Scots pine (Pinus sylvestris), lodgepole pine (Pinus contorta, black pine (Pinus nigra) and eastern white pine (Pinus strobus). By the end of August it became apparent that only Scots pine had become colonised and that on the other pines the insects had died. The settled sistens nymphs seemed to prefer the axis of the needle-bases to other parts of the shoot.

We have not so far observed the remaining parts of the life cycle. To summarise, there are several generations of apterous sistens and other forms between August and the following spring when sexuparae are produced which migrate back to spruce. The sexuparae produce small wingless males and females which mate, and the females lay eggs on Caucasian spruce. These hatch to give fundatrices which overwinter, and then induce the characteristic galls on Caucasian spruce.

 

Other aphids on the same host

Primary hosts

Pineus orientalis has been recorded from 5 or 6 Picea species (Picea jezoensis, Picea orientalis, Picea polita, Picea pungens and Picea torano and possibly Picea abies).

Secondary hosts

Pineus orientalis has been recorded from 54 Pinus species (including Pinus brutea, Pinus densiflora, Pinus mugo, Pinus sylvestris and Pinus thunbergi). N.B. Information on the Pinus hosts used by Pineus orientalis is likely to be unreliable given the impossibility of differentiating the species from Pineus pini by morphological characteristics.

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

Pineus orientalis is indistinguishable morphologically from Pineus pini at the sistens stage, and presumably causes similar levels of damage. For Pineus pini, infestation causes premature needle shedding and reduction in the length of infected needles, reducing productivity and leading to up to 50% loss of growth increment (Day et al., 2003) and up to 20% tree mortality (Odera, 1974). Stress can make pine trees more vulnerable to attack (Madoffe and Austara, 1993; Day et al., 2003). Damage to trees is most severe under warm, dry conditions.

Minimising stress to trees by applying good forest health practices will reduce the severity of damage. Avoiding planting Caucasian spruce near susceptible Pinus species is also beneficial. Classical biological control has been used in some countries - for example introduction of Leucopsis in Hawaii, Exochomus in Kenya and Australia and various coccinellids in Zimbabwe - and we have ourselves observed coccinellids predating Pineus adelgids in Britain.

Acknowledgements

We especially thank the UK Forestry Commission Bedgebury Pinetum for their kind assistance, and permission to sample.

Our particular thanks to Roger Blackman for images of his clarified slide mounts.

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

  • Carter, C.I. (1971). Conifer Woolly Aphids (Adelgidae) in Britain. Forestry Commission Bulletin No. 42. Forestry Commission, London Full text

  • Day, R.K. et al (2003). Biological control of homopteran pests of conifers in Africa. Pineus boerneri. pp. 104-106 In: Neuenschwander, P., Borgemeister, C. & Langewald, J. (eds). Biological control in IPM systems in Africa. CABI, Walling ford, UK. Full text

  • Madoffe, S.A. & Austara, O. (1990). Impact of pine woolly aphid, Pineus pini (Macquart) (Hom., Adelgidae), on growth of Pinus patula seedlings in Tanzania. Journal of Applied Entomology 110(4), 421-424. Full text

  • Mailu, A.M. et al. (1978). Evaluation of pine woolly aphid damage to Pinus patula and its effect on yield in Kenya. East African Agricultural and Forestry Journal 43(3), 259-265. Full text

  • Odera, J.A. (1974). The incidence and host trees of Pine woolly aphid, Pineus pini (L.) in East Africa. Commonwealth Forestry Review 53(2), 128-136. Full text