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Eomacrosiphon aphidsOn this page: Eomacrosiphon nigromaculosum
The monospecific genus Eomacrosiphon was established by Hille Ris Lambers (1958) with only a very brief description of its characteristics. The antennal tubercles of the aptera are very distinct (described by Pike et al., 2003 as 'moderately developed'), and the front is strongly concave. Antennal segment III is constricted at its base to just over half its diameter slightly nearer the apex. The first tarsal joints have 5 hairs. Marginal tubercles are present on the pronotum, sometimes 2 pairs, and more-or-less regularly on each of abdominal segments I to VII. The marginal tubercles are often compound or raspberrylike, and very conspicuous. The siphunculi are unusually thick, cylindrical or slightly tapering, very densely and heavily imbricated, and with very small hexagonal cells in the reticulated area. The forewing of the alate has an apical pigmented spot.
The only known species feeds on wild rose (Rosaceae) in western North America. It is assumed to be monoecious holocyclic, with alate males - but Jensen has found nascent colonies on an unrelated host, mountain tobacco (Arnica), indicating it may be dioecious.
Eomacrosiphon nigromaculosum (Black & red rose aphid) Western USA, Canada
Adult apterae of Eomacrosiphon nigromaculosum (see first picture below) are bright red with black bands or black patches on the dorsal abdomen; the body is truncate posteriorly, and the black siphunculi are held erect. (The fundatrix of this species, see second picture below, differs from apterae in later generations in having shorter antennae and shorter thicker siphunculi.) Antennal segments are pale except for the apices of segments V and VI which are dark. There are no secondary rhinaria on the antennae of the aptera (cf. Macrosiphum rosae, which do have secondary rhinaria on the antennae of the aptera). The rostrum reaches the second pair of coxae. The legs are pale brownish yellow, except for the tips of the femora and tibiae, and all the tarsi which are dark. The first tarsal joints have 5 hairs. There are rather long hairs on the hind tibia. Marginal tubercles are very conspicuous, and present on the pronotum and more or less regularly on each of abdominal tergites I to VII. The siphunculi are unusually thick, very densely and heavily imbricated, with very small hexagonal cells in the reticulated area. The siphunculi are completely black (cf. Ericaphis fimbriata, Ericaphis scammelli and Metopolophium dirhodum, which have partially or wholly pale siphunculi). The cauda is rather slender, and bears 4-5 pairs of lateral hairs. The body length of adult Eomacrosiphon nigromaculosum apterae is 2.0-2.8 mm.
Images above copyright Andrew Jensen, under a creative commons licence.
The alate Eomacrosiphon nigromaculosum (not pictured) has the head and thorax black, and the abdomen red, with a black band across tergites V and VI, and broken white intersegmental lines between all tergites. The antennae have segments I and II blackish, and the remainder dusky. The cauda and legs, except the tips of the segments, are yellow. The tarsi, tips of tibiae and siphunculi are black. The fore wing is dusky at the tip between the radial sector and media.
Eomacrosiphon nigromaculosum is found on various wild and cultivated rose (Rosa) species in western North America. These aphids cluster in masses along the stems, seldom spreading to the buds or leaves. Most accounts assume the species is monoecious, and remain on rose all year, but Jensen reports finding 'nascent' colonies of Eomacrosiphon nigromaculosum on an unrelated host - mountain tobacco (Arnica). Whether this is a true summer host, or merely an accidental host utilized during the dispersive phase, is as yet unclear. Eomacrosiphon nigromaculosum is holocyclic, with alate males. The black-and-red rose aphid is restricted to western USA and Canada.