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Aphids on walnut

Blackman & Eastop list about 20 species of aphids  as feeding on walnut species worldwide, and provides formal identification keys for aphids on Juglans. About 20 species of aphids feed on the various species of walnut worldwide. The main aphid genera are Stomaphis, Panaphis, Chromaphis and Monelliopsis; the latter is exclusively North American.

Of the 8 aphid species Blackman & Eastop list as feeding on European Walnut (Juglans regia) Baker (2015)  lists 3 as occurring in Britain: Chromaphis juglandicola,  Myzus persicae  and Panaphis juglandis. 

Bell et al. (2015)  (Appendix S2) have also published an "annotated checklist of aphids present in the UK". We discuss some of the reasons for the differences between Baker's and Bell's lists in our rare aphids page. 

The species below are those we have found most frequently, listed in rough order of abundance. Note that walnut is prone to having accidentals attempting to feed on it, such as the common sycamore aphid (Drepanosiphum platanoidis ). Assistance on identifying European walnut is given below. 

 

Chromaphis juglandicola (Small walnut aphid)

Adult viviparae are all winged. Fourth instar nymphs (first picture below) are yellowish white, and (in autumn) have paired brown spots on abdominal tergites 4 and 5. The alates (second picture below) are yellowish-white with pale brown thoracic lobes and paired brown spots on abdominal tergites 4 and 5. The antennae have dark brown tips and are about half the length of the body; the terminal process is 0.2 times the length of the base of the last antennal segment. The siphunculi are conical and smooth. The body length of alates is 1.2-2.3 mm.

 

The small walnut aphid lives scattered on the undersides of leaves of walnut (Juglans regia). Oviparae and males occur in May-June in India, and in autumn in Europe and the USA. It is found in Europe, Central Asia, India, Pakistan, China and North America.

 

Panaphis juglandis (Large walnut aphid)

All viviparae are alate. The fourth instar nymph (first picture below) has transverse rows of brown patches on the dorsal abdomen. The adult alate (second picture below) is large and stout-bodied. It has a darkened head and thorax, and a yellow abdomen with dark brown transverse bands. The forewing veins are fuscous-bordered. The siphunculi are short and truncate. The body length of the alate is 3.5-4.3 mm.

 

They live on the upper sides of leaves of walnut (Juglans regia), in rows along the veins, and are often ant-attended. Sexual forms occur in September-October. The species is rarely found together with the small walnut aphid, supposedly because it is adversely affected by the rain of honeydew from the other species. It occurs in Europe, and parts of central Asia, Pakistan and was introduced into the western USA.

 

Myzus persicae (Peach-potato aphid)

The apterae of Myzus persicae are generally yellowish-green (see first picture below) but vary from whitish or pale yellowish green to mid-green, rose-pink or red (see second picture below). They are often darker in cold conditions. The antennae are 0.7-1.0 times the body length, reaching to the siphunculi. Their siphunculi are slightly swollen towards the darkened tips and are 1.9-2.5 times the lerngth of the rather pointed cauda. The body length of Myzus persicae apterae is 1.2-2.3 mm.

 

The alate Myzus persicae (shown below) has a solid pigmented area occupying the mid-abdominal dorsum from segments 3 to 6, as well as further bars on adjoining segments.

The peach-potato aphid does host alternate where the primary host - peach (Prunus persica) occurs. Eggs are laid on the primary host and spring colonies curl the young leaves. However, most of the population overwinters as mobile stages on herbaceous plants and brassicas. Myzus persicae is a major pest on its summer hosts including potatoes, sugar beet, lettuce, brassicas and legumes, mainly because it transmits a number of important plant viruses. Myzus persicae is a polyphagous generalist.

 

Species of walnut

We cover only one species of walnut, the European walnut (Juglans regia), shown flowering below. The leaves are alternately arranged, 25-40 cm long each with 5-9 leaflets.

Acknowledgements

We have made provisional 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

  •  Blackman, R.L. & Eastop, V.F. Aphids on the world's plants An online identification and information guide. Full text