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Pseudacaudella aphidsOn this page: Pseudacaudella rubida
Pseudacaudella are very small, moss-living aphids. The antennal and median frontal tubercles are very low (cf. Myzodium which has well developed, rounded, rather flat antennal and median frontal tubercles). The antennae are 6-segmented, and shorter than the body; the apex of the terminal process is pointed and rather smooth, with 0-2 hairs. There are no secondary rhinaria in the aptera. First tarsal segments have 2 indistinct hairs. The dorsum is sclerotic, and the cuticle of the body margins is granulate. The siphunculi are cylindrical, imbricated or scabrous, with a terminal aperture. The cauda has its distal part much narrower than the proximal part.
There is only one species in the genus Pseudacaudella. It is most likely monoecious on mosses, although there is a single report of it host alternating from Sorbus to moss in Ukraine. It is anholocyclic over most of its range, and has a specialised overwintering second instar. It is found in northern Europe and eastern USA, but may have a much wider distribution, since it has also been observed in New Zealand, South America and North Africa.
Pseudacaudella rubida (Chilled-out moss aphid) Northern Europe, Eastern North America, possibly cosmopolitan
Adult apterae of Pseudacaudella rubida are olive-green to brown with dark siphunculi. In the brown forms, there are often rusty spots at the siphuncular bases. The dorsum of the adult is mostly smooth, sclerotic, and rather shiny, but nodulose on the margins. Antennal tubercles are undeveloped(cf. Myzodium modestum & Myzodium mimulicola, which have antennal tubercles developed as rounded, densely nodulose bosses). The head cuticle is almost smooth dorsally, with nodules on the ventral side. The antennae are 0.7-0.9 times the body length, with a terminal process 1.8-3.1 times as long as the base of antennal segment VI. There are no secondary rhinaria. The hairs on antennal segment III are about 0.3-0.5 times the basal diameter of that segment. The rostrum reaches to the hind coxae, and the apical rostral segment is 1.3-1.6 times the second hind tarsal segment. The siphunculi are cylindrical (cf. Decorosiphon corynothrix, which has siphunculi swollen on the distal half), with a subapical constriction under the strongly developed flange (cf. Muscaphis escherichi & Muscaphis cuspidata, which have no subapical constriction of the siphunculi). The siphunculi are 2.3-3.3 times the caudal length. The cauda has a broad rounded basal part, and a narrow tongue-shaped apical part, with 4 hairs. The body length of adult Pseudacaudella rubida apterae is 0.7-1.0 mm.
First two images above copyright Anders Albrecht, third image copyright CBG Photography Group,
Alate viviparae of Pseudacaudella rubida are shiny, and coloured as the apterous viviparae. The antennae are nearly as long as the body, with secondary rhinaria distributed 7-15 on segment III, 3-7 on segment IV and 0-2 on segment V. The siphunculi are 2.5-3.5 times the cauda, and are thinnest in the middle. Immature Pseudacaudella rubida normally have a membranous, unpigmented dorsum, no flange on the siphunculi, and have no wax powder. Overwintering nymphs (see second picture above), so-called 'winter larvae' (Muller, 1973), have a sclerotized, pigmented dorsum, and a thick wax coating to provide protection from adverse winter conditions.
Pseudacaudella rubida is found on mosses in several genera including Acrocladium, Climacium, Dicranum, Hylocomium, Mnium, Pleurozium, Polytrichum, Pseudoscleropodium, and Thuidium. Müller (1973) found Pleurozium schreberi and Scleropodium purum to be the most favoured hosts. It was able to survive in dry as well as humid habitats, and is not ant-attended. It is adapted for anholocycly, with a specialised overwintering second instar which has a dark sclerotic cuticle and a wax coat. However there is possibly host alternation from Sorbus in Ukraine. Pseudacaudella rubida has been found in Europe, Kazakhstan, Morocco, & North & South America, and alatae have been trapped in New Zealand