This species is associated mainly with grasses, but will also occur on cereals, overwintering
either in the egg stage or, more frequently, as adults. There are no non-poaceous hosts and, hence, no alternation of generations in the life-cycle. The aphids are similar in appearance to Metopolophium dirhodum (p. 115) but slightly smaller (up to 2.2mm long), yellower in colour and without the dark longitudinal dorsal stripe; a reddish form also occurs.
The shallot aphid is an often common pest of herbaceous plants, including beet, lettuce, onion (Plate 2d), potato, shallot, strawberry and various ornamentals. Infestations lead to considerable stunting, distortion and malformation of the foliage or flower trusses of host plants; subsequent growth from previously infested bulbs or corms in store may also be affected when these are planted out, the new shoots often being weak and noticeably distorted. Damage to strawberry crops (a winter host) tends to be patchy and sporadic, typically occurring in the early spring but usually only if the late winter has been mild. Shallot aphid is also a virus vector.
This species breeds parthenogenetically throughout the year, often surviving the winter on stored bulbs, corms and root vegetables, and on various glasshouse plants. Under mild conditions, colonies can also survive the winter out-of-doors (e.g. on strawberry). Winged migrants appear in the spring, and these spread infestations to various herbaceous plants; colonies on winter hosts often then die out.
Aptera 1.1-2.2 mm long, pale shiny brown, greenish-brown or yellowish-brown, distinctly convex; siphunculi pale, moderately long (but shorter than the third antennal segment) and the apical half distinctly swollen; cauda triangular, hardly visible from above (at least in live specimens) (Fig. 190d); head with lateral tubercles slightly convergent.
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