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Pine woolly aphid, Scots pine adelgidOn this page: Identification & Distribution Biology & Ecology Life cycle Other aphids on the same host
Identification & Distribution:
In life the apterous female of Pineus pini, known as the 'sistens' (see first picture below), is covered in white wax wool. Under the wax the sistens (see second picture below) is dark brown to dark redand almost spherical. The head and prothorax are heavily chitinized. The antennae are 3-segmented. There are small, separated wax gland facets on the head-prothoracic shield (cf. Pineus strobi and Pineus pineoides which have wax gland facets with polygonal lumina). The meso- and meta-thoracic plates are chitinized and fuse to form transverse segmental bars. The abdomen has four distinct pairs of spiracles and an ovipositor. The adult Pineus pini aptera has a body length of 1.0-1.2 mm and a width of 0.8-1.0 mm.
Image of alate above copyright Paul Piron, all rights reserved.
The winged female (third picture above) is mainly reddish grey with 5-segmented antennae. The forewings are hyaline and the veins are tinged with red. The body length of the Pineus pini winged form is 1.0 -1.2 mm.
Note: We cannot be certain that the alate is Pineus pini and not Pineus orientalis, since both species occur on Pinus mugo and they are indistinguishable on morphological characteristics. Pineus pini remains on pine all year, whilst Pineus orientalis host alternates between spruce and pine.
The pine woolly aphid has lost host alternation and sexual reproduction and remains all year on pine (Pinus sylvestris, Pinus nigra and Pinus mugo). Some authorities suggest this species derived from Pineus orientalis by shedding its primary host and reducing the number of forms. Pineus pini has an overwintering generation on the twigs, and two or more overlapping generations attacking the current year's shoots. Pineus pini eggs are laid in abundant wax-wool. The second of the summer generations in May-June includes winged forms which disperse to other pine trees. Young seedling pines are commonly infected by first-instar crawlers dispersed by wind.
Biology & Ecology
In Western Europe the Pineus pini life cycle is anholocyclic. Colonies can always be found on the smaller stems and shoots of pine throughout the year with three or more generations per year.
Pineus pini overwinters as immature forms from eggs hatching in early October. In November immature forms can be seen and these remain in their second or third instar until the following spring when they became mature sistentes. These start to lay their eggs in March. The egg clutches reach maximum size in the second half of April. Large clusters of eggs are laid which results in considerable differences between the hatching dates of the first and last eggs. The picture below shows the large clutches of Pineus pini eggs with sistens on pine in May. Note this colony has been treated with alcohol to remove the wax covering.
The spring generation of progrediens resulting from these eggs crawls on to the new growth and develops into two distinct morphs by the end of May. These are the apterous progredientes and winged sexuparae.
Image above copyright Paul Piron, all rights reserved.
The apterae continue to feed and reproduce on the pine, but the sexuparae fly away. The flight period extends from late May till the end of June. Presumably most of the sexuparae settle on pine, but some may settle on fir (Picea) after a period of active flight. This latter behaviour is considered a vestige of the holocycle.
Other aphids on same host:
Pineus pini has been recorded from 22 Pinus species, and 'Pineus pini spp. gp.' has been recorded from a further 7.
Blackman & Eastop list about 170 species of aphids as feeding on pines worldwide, and provides formal identification keys for aphids on Pinus.