Sitobion avenae F Grain aphid

The grain aphid is an important pest of winter wheat; infestations also occur on other cereals, including barley, oats, rye and sweet corn, and various grasses. Infested young plants may lack vigour. However, more important damage is caused later in host-plant development when aphids feed on the developing grain. Yield losses are especially severe if heavy attacks develop before the milky-ripe stage; the quality of infested grain is also affected. Once the developing grains harden, infestations are of little or no significance. This aphid is the main vector of barley yellow dwarf virus (BYDV) in eastern and northern Britain (cf. bird-cherry aphid, Rhopalosiphum padi, p. 119); it is also of significance as a virus vector in continental Europe.

Early-sown winter cereals are especially at risk from immigrating aphids that arrive in September and October from grasses and cereal stubble. Aphids on maize and sweet corn are capable of transmitting maize mosaic virus; however, colonies on these crops usually develop relatively late in the season and are rarely populous (cf. bird-cherry aphid, R. padi, p. 119).

BIOLOGY

Eggs, which overwinter on cereals or grasses, hatch in March. Colonies of wingless aphids then develop, especially on the uppermost leaves (Plate 2e) and on the emerging or emerged ears of winter wheat; usually, they do not become populous until late June. Winged forms occur during the summer and these spread infestations to other cereals and grasses, where further colonies of wingless aphids are initiated. Aphid development during the summer is rapid in hot, dry weather, and the potential for colony growth is especially great on wheat. In the autumn, winged sexual forms are produced and these eventually give rise to a generation of egg-laying oviparae. In mild regions, however, this pest lacks a sexual phase and survives the winter as either winged or wingless viviparous females.

DESCRIPTION

Aptera 1.5-3.Omm long, shiny yellowish-green to dark reddish-brown; antennae uniformly dusky; siphunculi long, black; cauda pale, about three-quarters as long as the siphunculi (Fig. 193c).

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