Aphidalia
General
The yellow rose aphid, Rhodobium porosum, is probably of North American origin but is now widely distributed in Europe, North Africa, parts of Asia and South America. It attacks plants of the family Rosaceae and is a pest of strawberries and roses.
Life cycle and appearance of Yellow rose aphid
Aphids have a complex life cycle, with both winged and wingless forms of adults and a great variety in colour. In greenhouses, reproduction takes place by parthenogenesis, with unfertilized viviparous females continuing to produce new generations of females. Aphids moult four times before reaching adulthood. With each moult they shed white skin, betraying their presence in the crop.
The yellow rose aphid is holocyclic in North America (i.e. they mate in autumn and produce eggs to overwinter). It is also holocyclic in parts of Europe, whereas throughout most of the world it is anholocyclic (i.e. only multiplying parthenogenetically with viviparous females continuously producing new generation of females) and generally found only on cultivated roses and strawberries, in glasshouses in northern Europe or outdoors in warmer climates.
Wingless yellow rose aphids have a brownish head; the body is bright yellow to yellow-green or green and rather shiny. Winged aphids have a bright green abdomen with black dorsal markings. The size of wingless adults is 1.2-2.5 mm, winged specimens are 1.4-2.2. mm
Damage symptoms
The yellow rose aphids usually live in young unfolded leaves. Nymphs and adults extract nutrients from the plant and disturb the balance of growth hormones. As a result, the plant’s growth is retarded giving rise to deformed leaves. Retarded growth and defoliation reduce yield.
Plant sap is rich in sugars, but has a low protein content. Aphids therefore need to extract large quantities of sap to get sufficient protein. The excess sugar is secreted in the form of honeydew, making the crop and its fruit sticky. Black sooty moulds grow on this honeydew, contaminating fruit and ornamental crops. At the same time, photosynthesis in the leaves is reduced, affecting production. The yellow rose aphid is also a vector of several viruses attacking strawberries and roses.