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Polyphagous aphids

Most aphid species are restricted to a single host-plant genus. Many can only raise successful colonies on one plant species. Host alternating species are similarly-restricted regarding their primary host, but much less so regarding possible secondary hosts. A small proportion of species (1 or 2%) can raise successful colonies on many plant genera, and are considered polyphagous. A few polyphagous aphids are now serious and cosmopolitan pests. That said, the term 'polyphagous' is not clearly defined. This is partly because their host preference is anything but uniform, but also because some species are only polyphagous in parts of their geographic range. Consequently their pest status varies: some are only considered pests in the tropics. Some are pests of ornamentals, or in special environments such as greenhouses, warehouses or hydroponic farms.

Blackman & Eastop provide a key to the 35 most polyphagous aphid species  worldwide: "species which occur numerous times in the host lists of many plant genera, and in some cases on plants in many different families". Their key to 23 polyphagous aphid species that feed typically on herbs or shrubs, but occasionally occur on trees,  has an additional 3 species.

Of those 38 aphid species, Baker (2015)  lists 25 as occurring in Britain: Acyrthosiphon malvae,  Aphis (Toxoptera) aurantii,  Aphis craccivora,  Aphis fabae,  Aphis gossypii,  Aphis nasturtii,  Aphis nerii, Aphis sambuci,  Aphis solanella, Aphis spiraecola, Aulacorthum solani,  Brachycaudus helichrysi,  Macrosiphum euphorbiae,  Myzus antirrhinii, Myzus ascalonicus,  Myzus cymbalariae, Myzus ornatus,  Myzus persicae,  Neomyzus circumflexus,  Pemphigus bursarius,  Rhopalosiphoninus latysiphon, Rhopalosiphoninus staphyleae, Rhopalosiphum padi,  Rhopalosiphum rufiabdominale and Smynthurodes betae.

Below we describe the top ten polyphagous aphids most commonly seen in Britain, grouped by genera. Note: In Britain Aphis spiraecola is rare and not considered a pest, Aphis craccivora is a minor pest mainly found in southern Britain, and Aphis nerii in Britain is only a greenhouse pest. Rhopalosiphoninus latysiphon, Rhopalosiphoninus staphyleae, Rhopalosiphum rufiabdominale and Smynthurodes betae are root / bulb / tuber aphids. Aphis solanella looks and generally behaves like Aphis fabae, Myzus antirrhinii looks rather like Myzus persicae but can form very large colonies, and Myzus cymbalariae is difficult to distinguish from Myzus ascalonicus.

 

Aphis fabae (Black Bean aphid)

Aphis fabae  is a black or very dark brown species with a variable abdominal sclerotic pattern - confined to abdominal tergites 6-8 in smaller apterae but broken bands present in larger ones. The siphunculi and cauda are dark. The antennae have joints of III-IV and base of V usually quite pale. Marginal tubercles are protuberant but small. The longest femoral and tibiae hairs are longer than the least width of tibiae. Apterae (see second picture below) often, and immatures (see first picture below) very often, have discrete white wax spots. The body length of apterae is 1.2-2.9 mm.

   

The black bean aphid host alternates between spindle (Euonymus europaeus) as the primary host and many herbaceous plant species as secondary hosts. Sexual forms occur in autumn. Aphis fabae is found throughout the northern continents, and has been introduced to many tropical and subtropical countries where it may reproduce parthenogenetically all year round. In Europe there is a complex of sibling species or subspecies which can only be distinguished by their choice of secondary host coupled with transfer experiments.

 

The nominate subspecies Aphis fabae fabae migrates to both broad beans (Vicia faba) (pictured above first) and poppies (Papaver spp.) (pictured above second) as well as Chenopodium spp. and beet (Beta vulgaris). It will not colonise thistle (Cirsium) or black nightshade (Solanum).

 

Aphis fabae cirsiiacanthoidis migrates to thistle (Cirsium arvense) (pictured above first) and Aphis fabae mordvilkoi to burdock (Arctium) (pictured above second). The fourth subspecies is Aphis fabae solanella which migrates to black nightshade (Solanum nigrum).

Although one can tentatively assign Aphis fabae on the plants above to a particular subspecies, they also colonise a huge range of other plants (for example many umbellifers) which are not associated with a particular subspecies. Also some hosts such as docks (Rumex spp) seem to be acceptable to all subspecies. Lastly (just to confuse things further) what was called Aphis euonymi  has now been renamed Aphis fabae evonymi, and Aphis fabae solanella has been renamed as Aphis solanella.

 

Aphis nasturtii (Buckthorn - Potato aphid)

The Aphis nasturtii  aptera is rather bright pale green to yellowish green and is not wax-powdered. The abdominal dorsum is membranous without dark bands or sclerites. The siphunculi are usually rather pale becoming a little darker towards the apex. The legs are dusky or rather pale. The body length of apterae is 1.1-2.4 mm. The alates have some variably developed dorsal bands but are always more lightly marked than Aphis frangulae  alates.

 

The buckthorn - potato aphid host alternates between common buckthorn (Rhamnus catharticus) as the primary host and many herbaceous plant species as secondary hosts, the most economically important of which is potato (Solanum tuberosum). Aphis nasturtii is now of almost world-wide distribution.

 

Aphis (Toxoptera) aurantii (Camellia aphid, Black citrus aphid)

Toxoptera aurantii  apterae are oval, shiny black, brownish-black or reddish brown in colour with rather short black-and-white banded antennae. The cauda and siphunculi are black, and the siphunculi are less than 1.5 times the length of the cauda. The cauda usually has less than 20 hairs (distinguishes from Toxoptera citricidus). A stridulatory apparatus is present. The body length of apterae is about 2 mm long.

The black citrus aphid is found on the underside of leaves of Citrus, as well as Tea (Camellia), coffee (Coffea) and mango (Mangifera). Infestation in spring can be very harmful to citrus crops. In temperate countries it is a pest of ornamental Camellia bushes. Adults stridulate by rubbing tibial spines on striae of the abdomen. The distribution is now cosmopolitan.

 

Aulacorthum solani (Glasshouse - potato aphid, Foxglove aphid)

The Aulacorthum solani  apterae are pear shaped and shiny greenish yellow, usually with a bright green or rust coloured patch at the base of each siphunculus. The antennae have darkened joints and are slightly longer than the body. The siphunculi are pale with dark tips, long, slender, tapered and distinctly flanged. The body length of apterae is 1.5-3.0 mm. The winged forms have darker antennae, legs and siphunculi and have a variably developed pattern of tranverse dark bars on the dorsal abdomen.

 

In temperate climates most of the population overwinters as nymphs or apterae, especially on potato sprouts and on many glasshouse plants and wild species such as foxglove (Digitalis). As a result, this is often one of the first aphid species to find on young plants in the spring. The high toxicity of the saliva of the glasshouse - potato aphid may produce deformation and discoloration of leaves being fed upon. This results in direct feeding damage to potatoes and peppers. It can also be a vector of about 40 plant viruses, but its relatively poor virus transmission efficiency makes it unimportant as a virus vector in the field. Its importance is much greater in glasshouses. Its distribution is virtually cosmopolitan.

 

Brachycaudus helichrysi (Leaf-curling plum aphid)

The adult Brachycaudus helichrysi  apterae on the primary host are variable in colour ranging from yellow to green to brown, often shiny with a slight wax dusting. On the secondary hosts they can be yellow, green, or almost white or pinkish. The antennae are shorter than the body with dusky tips. The dorsum of the abdomen is without a black shield. The siphunculi are pale, tapered and short - 0.8-2.0 times the length of the cauda. The cauda is pale, short and blunt. The body length of apterae is 0.9 - 2.0mm.

 

The leaf-curling plum aphid host alternates between various plum (Prunus) species (especially domestic plum and blackthorn) and a wide range of Asteraceae such as asters, chrysanthemums, yarrow and groundsel. This aphid is a serious pest on fruit trees. The populations on red clover Trifolium pratense) have been called var warei, but are not thought sufficiently distinct to warrant subspecific status.

 

Macrosiphum euphorbiae ( Potato aphid)

The Macrosiphum euphorbiae  apterae are either green with a darker green longitudinal stripe or red, often rather shiny. The eyes are reddish and the antennae are darker towards their tips. The femora are brownish and rather pale with the apices not dark or only slightly so. The siphunculi are pale sometimes with the tips darker, but not as dark as the tips of the tibiae. They are reticulated on the apical 13-20% and 1.7-2.2 times the length of the cauda. The cauda is rather pointed and not constricted. The body length of apterae is 2.0-4.0 mm.

 

Macrosiphum euphorbiae is a common and highly polyphagous species, which is often a pest on various crops such as potato (Solanum tuberosum), lettuce (Lactuca sativa) and beets (Beta vulgaris) as well as on numerous garden ornamentals. It is a vector of about one hundred plant viruses. It usually overwinters as viviparae, but it can produce sexual forms and eggs on rose. Aphid numbers increase rapidly from early spring, and alates spread infestations to other plants. It is an especial problem in unheated greenhouses. Macrosiphum euphorbiae was originally a North American species but was introduced to Europe about 1917 and is now cosmopolitan.

 

Myzus ascalonicus (Shallot aphid)

Myzus ascalonicus  apterae are quite small and shiny pale green to dirty yellow. Their legs and antennae are pale, apart from the ends of the antennae and the tarsi. The siphunculi are shorter than antennal segment III, distinctly swollen towards the apex, evenly coloured throughout and with only a very small flange. The cauda is roughly triangular in shape, and short: about one third the length of the siphunculi. The body length of Myzus ascalonicus apterae is 1.1-2.2 mm.

 

The shallot aphid does not host alternate, but is extremely polyphagous feeding on crops such as onions, shallots, strawberries, lettuce, brassicas and potatoes and many garden ornamentals. There is no sexual stage in the life cycle and no eggs are produced. Instead Myzus ascalonicus is cold-hardy and overwinters in glasshouses and sheltered areas. Numbers may build up even at low temperatures in winter and spring, with alates migrating to other crops up to mid-June.

 

Myzus ornatus (Ornate aphid, Violet aphid)

The Myzus ornatus  apterae are somewhat dorso-ventrally flattened. The dorsum is sclerotic, pale yellow or green, marked with conspicuous dark green or brownish pigmented paired intersegmental sclerites. The body length of apterae is 1.0-1.7 mm.

The ornate aphid does not host alternate and is extremely polyphagous. It is an important pest on crucifers, cucurbits and onions and also attacks peas, soybean, strawberry and many garden ornamentals. It also feeds on some trees such as Catalpa and Prunus, often feeding away from the main veins. Myzus ornatus occurs throughout the world.

 

Myzus persicae (Peach-potato aphid)

The Myzus persicae  apterae (first picture below) are generally yellowish-green but vary from whitish or pale yellowish green to mid-green, rose-pink or red. They are often darker in cold conditions. The siphunculi are of medium length and slightly swollen towards the darkened tips. The body length of apterae is 1.2-2.3 mm. The alate (second picture 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. The aphid 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. Whilst Myzus persicae is a generalist, the subspecies Myzus persicae nicotianae is a tobacco specialist.

 

Neomyzus circumflexus = Aulacorthum circumflexum (Crescent-marked lily aphid)

The Neomyzus circumflexus  apterae are shiny whitish, yellowish or green with black cross bands on thoracic segments, broken along the midline, and a large horseshoe-shaped spot on the back of the abdomen. The siphunculi are dusky with a darker flange, rather thick and cylindrical and 1.8-2.3 times the length of the cauda. The body length of apterae is 1.2-2.6 mm.

The crescent-marked lily aphid is entirely parthenogenetic with no sexual stage in the life cycle. In temperate climates it is primarily a pest of glasshouse crops where it attacks Asparagus, Begonia, Fuchsia and many others. Heavy infestations cause direct harm to many ornamental plants, and the aphids also transmit viruses. Neomyzus circumflexus has a cosmopolitan distribution.

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