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Iris aphidOn this page: Identification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Adult apterae of Aphis newtoni are generally described as being dark green to dark greenish brown or black. However, our own (limited) experience in southern Britain is that most Aphis newtoni populations range from a dark reddish brown (see pictures below) to blackish. The dorsal sclerotic pattern is similar to that of others of the 'black aphid' group - namely transverse bands on tergites 7-8, marginal and postsiphuncular sclerites and some paired spinal sclerites on tergites 1-6. Marginal tubercles are protuberant and conspicuous and are visible in the first picture of the live aphid below. The body length of the Aphis newtoni aptera is 1.78-2.15 mm.
Aphis newtoni siphunculi are dark and 0.94-1.35 times the length of the dark cauda. The hairs on the femora and tibiae (see micrographs below of apterae in alcohol) are almost all much longer than the least width of the tibiae.
The alates of Aphis newtoni are similar to the apterae, but with larger sclerotic bands and more protuberant marginal tubercles.
The Iris aphid feeds in large ant-attended colonies on iris, often the yellow iris (Iris pseudacorus). Oviparae and apterous males are produced in autumn. Aphis newtoni is distributed across Europe (except Scandinavia) and in Korea and Mongolia.
Biology & Ecology:
Large colonies are characteristic of Aphis newtoni, as shown on a cultivated white iris plant below.
The aphids are usually attended by ants, especially Lasius niger (see picture below).
Although Lasius were attending, they made no attempt to defend the aphids. On the contrary, the ants scattered at the the first sign of danger, to such an extent that it was difficult to photogrtaph an ant and aphids together. In Dunbartonshire, Scotland Muir (1959) found large thriving clonies of Lasius niger (a rare ant in the area) associated with Aphis newtoni, but in that case the ants had constructed earthen shelters around the bases of yellow iris leaves.
There are few reports in the literature of natural enemies attacking Aphis newtoni. Stary (2014) reports Lysiphlebus fabarum parasitising this species on Iris germanica. The first image below shows an unidentified parasitoid (centre right) attacking Aphis newtoni, on cultivated white iris. The second image below shows a group of, mainly empty, parasitized mummies apparently of Aphis newtoni on yellow flag (Iris pseudacorus).
In autumn oviparae (see picture below) and males are produced.
Damage and control
Alford (2012) includes Aphis newtoni as a pest of Iris, noting that large numbers often build up on the lower of the leaves and later on the young flowers.