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American hairy rose aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult apterae of Chaetosiphon thomasi (see first picture below) are pale yellowish green. Their antennal tubercles are rather well developed, whilst the median frontal tubercle is small, but conspicuous through the presence of two capitate hairs. The antennae are about as long as the body, and the terminal process is 3.8-4.9 times as long as the base of antennal segment VI. The apical rostral segment (RIV+V) is 0.06-0.08 times the body length (cf. Chaetosiphon fragaefolii on Potentilla, whose RIV+V is 0.08-0.11 times its body length). Abdominal tergites I-VII bear long and usually thick body hairs, with expanded or capitate apices, often much longer than the basal diameter of antennal segment III, and arising from prominent tuberculate bases. The dorsum is entirely pale with no pigmentation (cf. Chaetosiphon jacobi on Potentilla in western USA, which has a brown sclerotic dorsum). The first tarsal segments have 5 hairs. The siphunculi taper towards the distal half, curve inwards and slightly downwards, and have a very distinct flange; they are more than 2.5 times as long as the thick, blunt cauda (cf. Chaetosiphon tetrarhodum on rose, whose siphunculi are less than 2.5 times its caudal length). The body length of Chaetosiphon thomasi adult apterae is 1.0-2.6 mm.
Note: In the 1980s two Chaetosiphon species, Chaetosiphon fragaefolii and Chaetosiphon thomasi, were thought to occur sympatrically on strawberry, rose and Potentilla, only distinguishable from each other by the number of submarginal setae. Following a detailed study on variations in karyotype (=chromosome number), chaetotaxy (=bristle arrangement) and morphology (=body proportions), Blackman et al. (1987) assigned the name Chaetosiphon thomasi to a rose-feeding species holocyclic on Rosa rugosa in British Columbia (but with some records on Potentilla) - with Chaetosiphon fragaefolii occurring on strawberry and Potentilla. However, some American workers still seem inclined to synonomize Chaetosiphon fragaefolii (as Chaetosiphon fragariae?) with Chaetosiphon thomasi (see Jensen in AphidTrek). For example, AphID use an image of Chaetosiphon fragaefolii for Chaetosiphon thomasi (habitus).
All images above by permission, copyright Claude Pilon, all rights reserved.
The alate Chaetosiphon thomasi (image below) has a dark sclerotic head and thorax. The abdomen is membranous, with a dark inverted trapezoidal sclerotic patch from tergite III-V, and transverse bars on tergites VI-VII. The antennae of alatae are usually just longer than the body, blackish and bearing 20-37 rather large, slightly protruding secondary rhinaria on segment III, 2-4 rhinaria on segment IV and 0-1 rhinaria on segment V.
Chaetosiphon thomasi is found on both wild and cultivated rose (Rosa) species and on some cinquefoil (Potentilla) species. Whether it feeds on silverweed (Potentilla anserina) is unclear - Blackman (Aphids on Worlds Plants) when describing the species, notes it does not feed on this host, but includes it in the listing for that plant. Chaetosiphon thomasi is found throughout North America, and has also been reported from Chile and Argentina.
Other aphids on the same host
Chaetosiphon thomasi has been recorded on 6 species of rose Rosa (Rosa acicularis, Rosa carolina, Rosa fendleri, Rosa foetida, Rosa gymnocarpa, Rosa rugosa).
Chaetosiphon thomasi has been recorded on 3 species of cinquefoil (Potentilla) (Potentilla gracilis, Potentilla norvegica, Potentilla pacifica).
Damage and control
Damage from Chaetosiphon thomasi to rose is similar to that caused by the related Chaetosiphon tetrarhodum.