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Western vetch aphid, Alfalfa aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult apterae of Macrosiphum creelii (see first picture below) have the body pale green (or pink or yellow), with a darker median line. The cauda and tibiae are pale to slightly dusky, and the siphunculi are dusky on the distal half. The antennae are dusky on segments I, II and the base of III, with the remainder blackish throughout. The hairs on antennal segment III are more than 0.5 times the basal diameter of that segment. The base of antennal segment VI is 1.4-2.0 times the apical rostral segment (RIV+V) (cf. Macrosiphum euphorbiae, which has the base of segment VI only 0.8-1.3 times RIV+V). The rostrum barely reaches the second pair of coxae. The siphunculi have a subapical zone of polygonal reticulation with at least 4-5 rows of closed cells. The cauda is tapering, without a noticeable neck, and bears 4-5 hairs on each side and a single dorsal preapical one. The body length of the adult Macrosiphum creelii aptera is 2.3-4.0 mm.
Note: This species (like many others) is morphologically very similar to a highly polyphagous aphid, Macrosiphum euphorbiae, which is is the only other Macrosiphum likely to occur on vetches. Adults of the two species can be discriminated using the character specified above. The second picture below shows an immature IV instar aptera, most likely Macrosiphum euphorbiae, but initially misidentified as Macrosiphum creelii on Bugguide. It was found in north-eastern, rather than western America, and has wax dusting very typical of Macrosiphum euphorbiae immatures.
First image above copyright Andrew Jensen, second image copyright Charlie Eisemann; both under a creative commons licence.
The alate vivipara of Macrosiphum creelii (not pictured) is similar to the apterous vivipara except that the head and thorax are pale brownish. There are 15-21 secondary rhinaria on antennal segment III.
Macrosiphum creelii is monoecious on a wide range of Fabaceae, especially vetches (Vicia spp.) and vetchlings (Lathyrus spp.). It was first described by Davis (1914), who reported this species was already a more-or-less troublesome pest on alfalfa (Medicago) in Utah and Nevada. He envisaged it could become as great a pest in the west as Macrosiphum destructor (=Acyrthosiphon pisum), and some years later Halfhill (1982) reported it had become increasingly abundant since the 1960s. Nowadays, however, the newly-invasive blue alfalfa aphid (Acyrthosiphon kondoi) seems to be considered a much more important pest. Palmer (1952) recorded Macrosiphum creelii as being rare in Colorado. More recently Jensen notes that just at the edge of high-tide water line on the public beaches of Oregon there often grows a large Vicia, and on that there is almost always the largest and most dramatic specimens of Macrosiphum creelii. In his local southern Oregon Ponderosa pine forests, it is uncommon, but widespread, on native Vicia and Lathyrus growing in the shade of conifers. Macrosiphum creelii is holocyclic, and is found in western North America.
Other aphids on the same host
Macrosiphum creelii has been recorded on 1 Medicago species (Medicago sativa).
Macrosiphum creelii has been recorded on 3 Vicia species (Vicia americana, Vicia faba, Vicia gigantea).
Macrosiphum creelii has been recorded on 1 Pisum species (Pisum sativum).
Macrosiphum creelii has been recorded 4 Lathyrus species (Pisum sativum).
Macrosiphum creelii has also been recorded on one Phaseolus species (Phaseolus vulgaris).