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Aphidinae : Aphis newtoni
 

 

Identification & Distribution

Adult apterae of Aphis newtoni (see first two pictures below) range from pale reddish brown to dark greenish black. The terminal process is 2.8-3.6 times as long as the base of antennal segment VI. The fused apical rostral segment (RIV+V) is relatively short at 0.86-0.98 times as long as the second hind tarsal segment. The dorsal sclerotic pattern is similar to that of others of the Aphis fabae '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 on most or all abdominal tergites and are visible in the first picture of the live aphid below (cf. Aphis fabae, which has marginal tubercles present on tergites I & VII, but small or absent on tergites II-IV). 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 siphunculi are dark and are 0.92-1.55 times the length of the cauda. The dark cauda is tongue-shaped, much longer than its basal width (cf. Dysaphis tulipae, which has the cauda helmet-shaped, no longer than its basal width). The body length of the Aphis newtoni aptera is 1.78-2.15 mm.

The alatae of Aphis newtoni (see second picture above) are similar to the apterae, but with larger sclerotic bands and more protuberant marginal tubercles. Immatures, especially alatoid fourth instars, often have paired pleural wax spots (see second picture below). The third picture below shows a large colony of Aphis newtoni with some of the adults showing pleural wax spots.

The images below show an adult aptera of Aphis newtoni, dorsal and ventral in isopropyl alcohol.

The Iris aphid is found in large ant-attended colonies on iris, often the yellow iris (Iris pseudacorus). It feeds low down on leaf blades and later on the young flower stalks. Oviparae and apterous males are produced in autumn. Aphis newtoni is distributed across Europe (except Scandinavia), and in Korea and Mongolia.

 

Biology & Ecology

Habitat

Large colonies are characteristic of Aphis newtoni, as shown on a Dutch iris plant below.

Colonies are usually initiated near the leaf bases where the aphids may be tented with soil particles by ants, but as the colonies grow they spread to cover the leaf blades (see above) and later the flowers stems and seed pods.

Life cycle

Aphis newtoni overwinters in the egg stage on the host plant, with the eggs hatching in April. The fundatrices and their offspring reproduce parthenogenetically, producing large colonies of aphids. Numbers generally peak in June or July (see picture below), declining somewhat in late summer as the predators take their toll on the population.

The sexuales develop in autumn. Males are apterous with very few secondary rhinaria. The oviparae have extended abdomens (see picture of oviparae below). The oviparae have only very slightly thickened hind tibiae bearing 0-20 scent plaques (pseudosensoria).

Colour

The colour of Aphis newtoni is quite variable, but we have found the most frequent colour form to be reddish brown. The reddish-brown aptera in the picture below has unusually well-marked transverse abdominal bands on all tergites as has the alate.

The immatures produced by reddish-brown apterae and alatae are also reddish-brown.

There is also a greenish-black form (see picture below of alate and adult aptera) which we have found rather less common.

On one occasion we found a very unusual 'white' form of the alate (see picture below) which was producing white immatures.

Ant attendance

Except when Iris plants are growing in water, Aphis newtoni are usually attended by ants, especially Lasius niger (see picture below).

Although Lasius often attend Aphis newtoni, in our experience they make no attempt to defend the aphids. On the contrary, the ants scatter at the first sign of danger, to such an extent that it can be difficult to photograph ants and aphids together.

In Dunbartonshire, Scotland Muir (1959) found large thriving colonies 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.

We have also found them being attended by Myrmica ants on one occasion (see picture below).

Myrmica ants were more ready to defend the aphids against potential threats.

Natural enemies

There are few reports in the literature of predators attacking Aphis newtoni, but we have found evidence of predation by cecidomyiid larvae. The alate below had a total of seven cecidomyiid eggs laid on its wing.

Cecidomyiids are usually reported to lay their eggs on the aphid host plants, but we have often found them laid on the aphids themselves. Syrphid eggs can also be seen laid in the colony (see picture below).

Stary (2014) reports Lysiphlebus fabarum parasitizing 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).

 

Other aphids on same host:

Aphis newtoni has been recorded on 20 species of Iris (Iris alberti, Iris aphylla, Iris foetidissima, Iris x germanica, Iris graminea, Iris halophila, Iris lactea, Iris locyzi, Iris lutescens, Iris orientalis, Iris pallasi, Iris pseudacorus, Iris pumila, Iris ruthenica, Iris scariosa, Iris setosa, Iris sibirica, Iris songarica, Iris spuria ssp. musulmanica, Iris uniflora).

Blackman & Eastop list 19 species of aphid as feeding on Iris species worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 16 as occurring in Britain (Show British list).

However yellow iris (Iris pseudacorus) has just 4 species known to feed on it - Aphis newtoni, Dysaphis tulipae, Macrosiphum euphorbiae, and Myzus ascalonicus - all of which occur in Britain.

 

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.

Acknowledgements

Whilst we make every effort to ensure that identifications are correct, we cannot absolutely warranty their accuracy. We have mostly made identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994) and Blackman & Eastop (2006) supplemented with Blackman (1974), Stroyan (1977), Stroyan (1984), Blackman & Eastop (1984), Heie (1980-1995), Dixon & Thieme (2007) and Blackman (2010). We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References

  • Alford, D.V. (2012). Pests of ornamental trees, shrubs and flowers: a colour handbook. Second Edition. Academic Press. Full text

  • Muir, D.A. (1959). The ant-aphid-plant relationship in West Dunbartonshire. Journal of Animal Ecology 28(1), 133-140. Full text

  • Stary, P. et al. (2014). Interference of field evidence, morphology, and DNA analyses of three related Lysiphlebus aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae). Journal of Insect Science 14(1), 133-140. Full text