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Flabellomicrosiphum [Macrosiphini]Flabellomicrosiphum are rather small aphids with a frosted appearance. The vertex is slightly convex. The antennal tubercles are only slightly developed, not noticeably exceeding the vertex. Secondary rhinaria on the antennae of alatae are round. Ocular tubercles are indistinct. The rostrum has the typical stiletto-shaped apical rostral segment (R IV+V) of aphids feeding on Anthemideae. The hairs on the body & appendages are broadly flabellate (=fan-shaped), giving the frosted appearance. Marginal tubercles are not evident. The siphunculi are merely raised pores. The cauda is elongate, conical or cylindrical, and the anal plate is rounded. The wing venation on the alate is as in genus Aphis. There are 2 species of Flabellomicrosiphum, both monoecious holocyclic on sagebrush (Seriphidium). They are related to Epameibaphis, Pseudoepameibaphis and the Palaearctic genus Coloradoa. Jensen notes that the two species placed in Flabellomicrosiphum should probably be considered as Pleotrichophorus with very short siphunculi, albeit it will take effort from the DNA experts to settle the question. Both species are North American. Flabellomicrosiphum knowltoni (Dark-legged_frosted_aphid) Western USAAdult apterae of Flabellomicrosiphum knowltoni (see first picture below) are dull slate grey to pinkish or greenish, overlaid with numerous pale fan-shaped hairs giving it a frosted appearance. The antennae are more than half the length of the body. The terminal process is more than twice the length of the base of antennal segment VI (cf. Flabellomicrosiphum tridentatae, which has the terminal process less than twice the base of antennal segment VI). The rostrum reaches the third pair of coxae. The dorsum bears numerous spatulate hairs. The coxae, trochanters and femora are black and the hind tibiae are pale to dusky (cf. Flabellomicrosiphum tridentatae, which has pale femora). The siphunculi are reduced to raised pores. The cauda is dark, and bears two to three pairs of lateral hairs plus three to four dorsal or dorso-lateral hairs. The body length of adult Flabellomicrosiphum knowltoni apterae is 0.9-1.5 mm.
First image above copyright Andrew Jensen, second image copyright Stan Shebs, The alate vivipara of Flabellomicrosiphum knowltoni is slightly darker than the aptera. The antennae are dusky, with segment III bearing 4 secondary rhinaria. The rostrum reaches beyond the second pair of coxae. The femora are dark, and the hind tibiae dusky. The siphunculi are merely raised pores. Flabellomicrosiphum knowltoni is monoecious holocyclic on big sagebrush (Artemisia tridentata = Seriphidium tridentatum) (see second picture above). Oviparae have been found in Utah in October. Flabellomicrosiphum knowltoni are apparently very active when disturbed (see Jensen in aphidtrek). Like its foodplant, its distribution is restricted to western USA. Flabellomicrosiphum tridentatae (Pale-legged_frosted_aphid) Western USAAdult apterae of Flabellomicrosiphum tridentatae (see picture below) are pale green, overlaid with numerous pale fan-shaped hairs giving it a frosted appearance. The antennae are more than half the length of the body. The terminal process is less than twice the length of the base of antennal segment VI (cf. Flabellomicrosiphum knowltoni, which has the terminal process more than twice the base of antennal segment VI). The rostrum reaches beyond the second pair of coxae, with the apical rostral segment (RIV+V) tapering, laterally compressed, and the tip beyond the hairs needlelike in ventral aspect. The dorsum bears numerous spatulate hairs. The legs including the femora (but not the tarsi) are pale (cf. Flabellomicrosiphum knowltoni, which has dark femora). The siphunculi are reduced to raised pores. The cauda is pale or dusky, and bears three pairs of lateral hairs. The body length of adult Flabellomicrosiphum tridentatae apterae is 0.9-1.5 mm.
Image above copyright Andrew Jensen under a creative commons licence. The alate vivipara of Flabellomicrosiphum tridentatae (not pictured) is similarly colored to the aptera. The antennae are black-tipped shading to pale at the base, with segment III bearing 4-5 large flat secondary rhinaria. The legs are pale with the tips of the tibiae and tarsi black. The siphunculi are truncate or slightly mammiform, without a flange, and hardly more than a raised pore. The cauda is tapering to parallel-sided, elongate, and rather acute, with 3-4 hairs on each side and 2-3 dorsal ones near the tip. Flabellomicrosiphum tridentatae is monoecious holocyclic on leaves and flower stems of big sagebrush (Seriphidium tridentata). Individuals are often found in rows, one behind the other on the leaves. Palmer (1952) describes this species as being rare. Jensen in Aphidtrek reports it to be locally common, but interestingly absent from large swaths of its host plant range; sagebrushes are known to be diverse in terms of plant chemistry, and it is possible that such variation in the plant controls the insect's distribution. The species is restricted to western USA.
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