Biology, images, analysis, design...
|"It has long been an axiom of mine that the little things are infinitely the most important" |
Genus Pineus [Adelgini]
Pineus aphids are distinguished by having only four distinct pairs of abdominal spiracles. Wingless adults on secondary hosts are pear-shaped or globular and have a fused and pigmented head and prothoracic shield. They generally secrete white wax-wool.
There are about 23 Pineus species through Europe, Asia and North America. The primary host of species with a sexual stage in their life cycle species is spruce (Picea), and the secondary host is pine (Pinus). The galls on spruce are usually on the shoot tips and are less compact than those of Adelges. Several Pineus species have lost sexual reproduction and host alternation, and instead live all year on spruce or pine.
Pineus orientalis (Spruce-pine woolly adelgid) Asia, Europe
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.
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.
Pineus pini (Pine woolly aphid, Scots pine adelgid) Europe, Africa, Asia
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 aptera has a body length of 1.0-1.2 mm and a width of 0.8-1.0 mm.
Image 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.
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.
Pineus strobi (Pine bark adelgid, Weymouth pine adelgid) North America, Europe, Asia
The aptera of Pineus strobi is dark brown or dark red, and is covered in dense white wax wool. The head-prothoracic shield is heavily sclerotized. The wax gland facets have polygonal lumina, similar in type to Pineus pineoides, but are generally more numerous, occurring in large groups over the shield. The adult body length is 0.75 - 0.9 mm and width is 0.6 - 0.8 mm. The eggs laid by the apterae measure between 0.26 and 0.28 mm long. The first picture below shows a dense colony of Pineus strobi on a branch of Pinus strobus - the live adelgids are obscured by the white wax 'wool', but some of the large orange-yellow eggs of Pineus strobi are visible.
The alate sexupara (see second picture above) is deep red. It is larger, but otherwise resembles the sexupara of Pineus pini. Alatae of Pineus strobi have the rhinarium on antennal segment V very large, more than half the segment length, with its basal portion about the same length as its terminal portion. Antennal segment III has a circular rhinarium when seen ventrally (cf. alate Pineus pini which have the rhinarium on antennal segment V less than half the segment length, and the basal portion of rhinarium clearly longer than terminal portion. Antennal segment III has a rhinarium that is broad and angular).
The usual host of Pineus strobi is eastern white pine (Pinus strobi), but where introduced it has also been recorded on Pinus cembra, Pinus pinea, Pinus sibirica and Pinus sylvestris. It is an anholocyclic 'species', so does not host alternate. Overlapping generations of sistentes and progredientes feed through the spring and summer on shaded parts of the trunk and undersides of the branches. The pine bark adelgid is native to North America, but has been introduced to Europe, and has also been recorded from western Siberia.