Damson - hop aphid
The adult wingless forms are small on their summer hosts, 1.1 - 1.8mm long, but medium sized on its winter hosts, 2.0 - 2.6mm long. They range from pale green to yellowish green, with darker green longitudinal stripes on the upper surface of the abdomen. The two tubes (siphunculi) at the rear end are pale, of medium length, thicker at their bases and slightly curved outwards at their tips. The tail (cauda) is short, pale and blunt. This species characteristically has a pair of sharply pointed head projections on the inside of the antennae. The winged form is 1.4 - 2.1mm long, and has a black patch of more or less fused cross bars on the upper surface of the abdomen. The projections on the head are much less developed in the winged form, and the tail more triangular and sharp.
Host plants/Life cycle
This species overwinters as eggs on Prunus spp., particularly on blackthorn, bullace, damson and plums. The eggs hatch between late February and April. After one or two generations of wingless aphids, winged forms begin appearing in the latter half of May. These winged forms migrate to the summer host, hops. This migration begins in earnest in early June and reaches a maximum in late June. It then declines and ends in late July or early August. It appears there is little movement within or between hops, and no further winged forms are produced until the autumn. A return flight to the winter hosts occurs in September and October. This species can stay on its winter host Prunus spp. throughout the summer, particularly on the sucker growth of plums.
On hops, this is the dominating pest species and is the main limiting factor to hop production. Routine pesticide application is required every year, at the very least at the beginning of the aphid flight. Heavy infestations reduce hop plant vigour and may induce defoliation. Even light infestations of the harvested hop cones can reduce their economic value. Added to this, it is able to transmit Hop mosaic carlavirus, Hop split leaf blotch virus and Hop line pattern virus. This species may also cause a little damage on plums, by curling young leaves and by transmitting Plum pox potyvirus.
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