Apterae of Rhopalosiphum nymphaeae are reddish-brown on the primary host (Prunus species – Plum and Blackthorn), and more or less shiny reddish-brown to dark olive on the secondary host (Water-lily). R. nymphaeae alatae are shining brown, sometimes with white dorsal wax markings. The R. nymphaeae aptera body length is 1.6 to 2.6 mm. For further information follow the ‘Further info:’ link below.

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In spring the Water Lily Aphid feeds on various Prunus species (such as Prunus spinosa) where it feeds on leaf petioles and fruit stalks curling the leaves. In early summer Rhopalosiphum nymphaeae alatae migrate to the secondary hosts comprising a large variety of water plants, including Nymphaea (Water-lilies), Potamogeton, and Sparganium.

Spring to autumn.

In Britain it is found from the south of England to the north of Scotland but is not well recorded.

Rarely recorded in Leicestershire and Rutland.

https://influentialpoints.com/Gallery/Rhopalosiphum_nymphaeae_water_lily_aphid.htm