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Pineus pini

Pine woolly aphid, Scots pine adelgid

On this page: Identification & Distribution  Other aphids on the same host 

Identification & Distribution:

The apterous female of Pineus pini, known as the 'sistens' (see first picture below), is dark brown to dark red, almost spherical. In life it is covered in white wax wool (see second picture below). 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 aptera has a body length of 1.0-1.2 mm and a width of 0.8-1.0 mm.

The winged female (not pictured) 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.

The pine woolly aphid has lost host alternation and sexual reproduction and remains all year on pine (Pinus sylvestris, Pinus nigra and Pinus mugo). There is 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

Life cycle

In Western Europe the 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 eggs with sistens on pine in May. Note the 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.

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:

Blackman & Eastop list about 170 species of aphids  as feeding on pines worldwide, and provides formal identification keys for aphids on Pinus.

Acknowledgements

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).

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