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Green horsemint aphidOn this page: Identification & Distribution Other aphids on the same host
Identification & Distribution
Adult apterae of Aphis agastachyos (see picture below of adult aptera with immatures) are oval shiny dark green, with no dorsal abdominal sclerotization. Their antennae are evenly pale or with darker apices, 0.5-0.6 times the body length. The antennal terminal process is 1.5-1.8 times the length of the base of antennal segment VI. The hairs on antennal segment III vary from blunt to very acute with the longest about 1.5 to 2.0 times as long as the basal diameter of the segment. The apical rostral segment (RIV+V) is about 1.25 times the length of the second hind tarsal segment (HTII) and has 4-8 accessory hairs. There are large marginal tubercles on abdominal tergites I and VII, bluntly conical, about as tall as their basal width. The legs are pale or (in alatiform specimens ?) with dark apices to the femora and tibiae. The siphunculi are pale, or dusky towards the tips, rather thick, evenly tapering to near the apex, with a wide flange and 1.4-2.0 (1.1-1.6 in Blackman) times the caudal length (cf. Eucarazzia elegans, which has the siphunculi strongly swollen and 5.4-8.2 times as long as the cauda). The cauda is darker than the siphunculi, thick, more or less bluntly triangular with 7-12 strongly curved hairs.
Image above copyright Andrew Jensen under a cc by-nc-sa licence.
The alate Aphis agastachyos has darker head, thorax, siphunculi, cauda and antennae than the aptera. The abdomen is coloured as the aptera, but there are bars on tergites VI & VII, spinal sclerites on tergites V and VI, and large dark marginal and postsiphuncular sclerites. The cauda is narrower than in the aptera, with up to 14 hairs.
Aphis agastachyos feeds on horsemint (Agastache spp.) and possibly wildmints (Monardella spp.), curling the leaves. The species is monoecious holocyclic with apterous males and oviparae being produced on horsemint. However, Hille Ris Lambers (1974) reported that they were not produced at the usual time (autumn), but in summer (July). Since the oviparous females contained no eggs, he suggested that either more productive oviparae might develop later in the year, or that the eggs had already been laid. If the latter is the case, it indicates an 'abbreviated' life cycle, possibly because the aphid can only feed on Agastache early in the year when leaves are soft and/or when there is sufficient soluble nitrogen available. Aphis agastachyos is found in western USA (Idaho, Utah, Oregon, Washington).
Other aphids on the same host
Aphis agastachyos has only been recorded from one giant hyssop / hummingbird mint species (Agastache urticifolia), but Jensen reports finding a very similar (or the same?) aphid species on another mint species, Monardella odoratissima.
Blackman & Eastop list 2 species of aphid as feeding on horsemint (Agastache urticifolia) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 15 as occurring in Britain (Show British list).