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Silverweed aphidOn this page: Identification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution
Adult apterae of Chaetosiphon potentillae (see first picture below) are yellowish or whitish. The head has well developed, angular, antennal tubercles and a large median frontal tubercle. The third antennal segment has 8-12 thick capitate hairs (cf. Chaetosiphon fragaefolii which can be found on silverweed and has 2-7 thick capitate hairs on that segment). The fourth and fifth antennal segment are usually without secondary rhinaria (cf. Chaetosiphon fragaefolii which has 2-10 secondary rhinaria on the fourth segment and 0-1 on the fifth). The dorsal hairs of apterae are thick and capitate and arise from tubercular bases. Siphunculi are pale, cylindrical, quite thin and with a well developed flange; they are 2.2-3.3 times longer than the cauda which is elongate triangular. The body length of the adult Chaetosiphon potentillae aptera is 1.4-2.1 mm.
The alate (see second picture above) is light green with a central dark patch and several dark transverse bands on the abdominal dorsum. The wing veins are dark brown. The micrographs below show dorsal views of an adult Chaetosiphon potentillae aptera, and an alate.
Chaetosiphon potentillae does not host alternate, but remains all year on silverweed (Potentilla anserina) and barren strawberry (Potentilla sterilis). Yellowish oviparae and brown apterous males develop in autumn, with overwintering eggs laid on the host leaves. Chaetosiphon potentillae is found throughout Europe and in North America.
Biology & Ecology
There is a history of confusion in the synonomy and identification of species in the genus Chaetosiphon, formerly Pentatrichopus (Capitophorus). Thomas & Jacob (1940) studied both Chaetosiphon potentillae and Chaetosiphon tetrarhodum in his study on the strawberry aphid Chaetosiphon fragaefolii because there was concern that these other species might also be able to live on strawberry. Chaetosiphon potentillae is now known to be confined to Potentilla species and Chaetosiphon tetrarhodum to Rosa species. However, Chaetosiphon fragaefolii is sometimes found on the host of Chaetosiphon potentillae, namely silverweed (Potentilla anserina).
Chaetosiphon potentillae do not form large colonies. They instead live singly or in very small groups.
The adult silverweed aphid (see picture above) moves about the plant depositing her nymphs in ones or twos on the leaves.
After a newborn nymph has been deposited on a leaf (see picture above), it moves to the leaf axil (the crotch between the leaf and stem).
Once there, it flattens itself and hides amongst the long hairs of the host plant (see picture above). This behaviour is described as cryptophilic (= concealment-loving).
In June many of the fourth instar nymphs develop wing buds (see picture below).
They moult to winged alates (see picture below) which disperse to other silverweed plants.
Sexuales develop in autumn. The slender- bodied brown males (first picture below) are apterous. The oviparae are yellowish (see second picture below) and the hind tibiae have a few large scent glands on the distal half.
After mating, the oviparae lay eggs on the host plant leaves.
The pictures above show (first) a newly laid egg of Chaetosiphon potentillae, and (second) a hardened (sclerotised) egg. The species overwinters in the egg stage, with the fundatrices hatching from the egg the following spring.
Other aphids on same host:
Blackman & Eastop (1984) list 23 species of aphids that feed on Potentilla anserina and Potentilla sterilis, worldwide.
Of those aphid species, Baker (2015) lists 18 as occurring in Britain: Acyrthosiphon boreale, Acyrthosiphon malvae, Anthracosiphon hertae Aphis craccivora, Aphis nasturtii, Aphis roepkei, Aphis tormentillae, Aulacorthum solani, Chaetosiphon fragaefolii, Chaetosiphon potentillae, Longicaudus trirhodus, Macrosiphum euphorbiae, Maculolachnus submacula, Myzaphis rosarum, Myzus ascalonicus, Myzus persicae, Pemphigus ?populi and Rhopalosiphoninus latysiphon.