Agriculture Reference
In-Depth Information
although the aphids are capable of transmitting
barley yellow dwarf virus (BYDV). Apterae on
cereals are broad-bodied (f .4-2.0 mm long),
yellowish-green and somewhat dusky, with short,
purplish-brown siphunculi. Those developing on
apple and pear in spring are larger (2.f-2.6mm
long), shiny yellowish-green to bright green,
with a darker dorsal stripe and mainly green
siphunculi; the siphunculi are distinctly flanged
(Fig.l91f).
Early-sown winter cereals are especially at risk
from immigrating aphids that arrive in Septem-
ber and October from grasses and cereal stubble.
Aphids on maize and sweet corn are capable of
transmitting maize mosaic virus; however, colo-
nies 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 colo-
nies of wingless aphids are initiated. Aphid de-
velopment 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.
Rhopalosiphum maidis
(Fitch)
Cereal-leaf aphid
This entirely viviparous, anholocyclic species
occurs only on members of the Poaceae, espe-
cially wild grasses. During the summer, it will
also infest cereal crops, especially barley, maize
and sweet corn. Apterae are c. 1.0-2.5 mm long,
and pale bluish-green and velvet-like, with a
small purplish patch at the base of each
siphunculus; the antennae are short and dusky,
and the legs and siphunculi black and relatively
short. The abdomen of alatae is uniformly yel-
lowish-green or dark green. Infestations are
rarely of significance in the UK, although the
aphids are vectors of viruses.
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).
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 in-
fested 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 signifi-
cance as a virus vector in continental Europe.
Sitobion fragariae
(Walker)
Blackberry/cereal aphid
This species overwinters in the egg stage on
blackberry, where heavy infestations in spring
cause significant leaf damage and also depress
fruit yields. In summer, colonies develop on vari-
ous cereals and grasses, which act as secondary
hosts. Although often invading the ears of wheat
and other members of the Poaceae, the aphids
are rarely numerous and, although capable of
transmitting viruses (e.g. BYDV), are of only
