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Are they useful or harmful?

When it comes to which insects kill and eat aphids, the role of 'ladybirds' (Coccinellid beetles) is well known - but the importance of several families of 'true-bugs', in the suborder Heteroptera, is less well known. This is probably because most of the true-bugs feed on plants. Indeed some are major pests in their own right, such as the tarnished plant bug (Lygus lineolaris, see first picture below) a mirid that feeds on a broad range of economically important crops in North America.

First image above: A pest bug, Lygus lineolaris, (tarnished plant bug) copyright Judy Gallagher under a Creative Commons Attribution 2.0 Generic license.
Second image above: A beneficial bug, Anthocoris nemorum (minute pirate bug).

Not all heteropteran bugs feed only on plants. A few families include species which are partly or wholly predatory on other arthropods. First and foremost amongst the bug families predatory on aphids is the Anthocoridae (see second picture above). These bugs contribute to the biological control of aphids and other insect pests.

Take care when handling Heteroptera:
Many species can deliver a painful bite to humans. Moreover, most of the 130 or more species in the Triatominae (Reduviidae) are haematophagous (feed on blood). The triatomines are responsible for the transmission of the protozoan blood parasite Trypanosoma cruzi to humans. This is the causative agent of Chagas disease, which is prevalent in the Americas from the southern United States to northern Argentina.

 

What are the (heteropteran) bugs?

Bugs in the suborder Heteroptera are often called 'plant bugs'. They include approximately 42,000 different species in a total of 90 families. They are often dorso-ventrally flattened and typically have two pairs of wings. The forewings are partly thick and protective and partly membranous; the tips overlap at rest. The hind wings are typically fully membranous. They have a prominent backwards-pointing triangular scutellum lying at the base of the folded wings. Some species of Heteroptera are wingless, or have very reduced wings (=brachypterous). The mouthparts are for piercing and sucking, and the antennae have 4-5 segments.

Heteroptera undergo incomplete (or gradual) metamorphosis with no pupal stage. They reproduce via sexually-produced eggs (see first picture below of eggs laid by the shieldbug Palomena prasina). Shieldbugs are unusual amongst insects in that they show parental care, usually remaining with the eggs till after they have hatched to protect them from predators.

The wingless immatures (nymphs) resemble the adults, with the wing pads becoming larger in successive moults. The second picture above shows a final instar nymph of a shieldbug, Elasmucha grisea.

The three largest families of the Heteroptera are the Miridae (plant bugs), Lygaeidae (seed bugs) and Pentatomidae (stink bugs). The Pentatomidae are grouped together with 14 other families in a superfamily Pentamoidea, the members of which are known as shield bugs. Most species of bugs in these three families feed on plants, but a few (mostly in the Miridae) are partly or wholly predaceous, and can be important for biological control of aphids and other pests. A few heteropteran families comprise only predaceous or haematophagous species. Some of these like the Gerridae and Notonectidae are aquatic and do not concern us here. But four terrestrial groups - the Anthocoridae (minute pirate bugs), Nabidae (damsel bugs), Phymatidae (ambush bugs) and Reduviidae (assassin bugs) - have some species which predate aphids to a greater or lesser extent.

 

Anthocoridae (Flower bugs, Minute pirate bugs)

Anthocorid bugs are small, elongate-oval, flattened insects, often patterned in brown, black and white. Adult anthocorids have two ocelli on the head, which distinguishes them from mirids. They have a piercing and sucking 3-segmented rostrum formed from the labium which is used to inject prey with digestive enzymes, and to suck up the food. The forewings, known as the hemelytra, have the proximal part sclerotized, and the distal part membranous, with both a cuneus (a wedge-shaped section at the end of the hemelytra) and an embolium (a strip along the leading edge of the hemelytra). The hind wings are membranous. Anthocorids are found on plant surfaces feeding on aphids or other soft-bodied arthropods, and in cryptic habitats such as inside aphid galls. The various species of the genus Anthocoris can be very difficult to tell apart.

 

Anthocoris nemoralis

Adult Anthocoris nemoralis are 3.5-4 mm in length. Antennal segments I, III and IV are usually dark, with only antennal segment II pale at the base (see two pictures below), (cf. Anthocoris nemorum which has segments II and III mainly pale with dark apices). The pronotum is black and the forewings are shiny only on the cuneus and embolium, and at the apex of the corium). The forewings of Anthocoris nemoralis are more darkly marked than on Anthocoris nemorum and the dark patch on the wing membrane does not resemble an hourglass. The femora are orange-brown but with a dark patch especially on the hind legs (cf. Anthocoris confusus which have very dark femora).

First image above copyright Mick Talbot under a Creative Commons Attribution 2.0 Generic license.
Second image above copyright B.J. Schoenmakers under a CC0 1.0 Universal Public Domain Dedication.

Anthocoris nemoralis is mainly found on trees, in contrast to the rather similar Anthocoris nemorum which is mainly found on herbaceous vegetation. It is considered as an important biological control agent against the pear psyllid, Cacopsylla pyricola. Predators are attracted by psyllid-induced plant volatiles to pear leaves that are infested and damaged by psyllids. There the female Anthocoris nemoralis lays an average of 140 eggs. This anthocorid also feeds on various species of aphids, and shows promise for control of aphids in greenhouses. Anthocoris nemoralis is found naturally in Europe and the Middle East, and has been introduced into North America.

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Anthocoris nemorum

Adult Anthocoris nemorum (see first two pictures below) are 3-4 mm in length. Antennal segments I and IV are usually dark, whilst segments II and III are mainly pale with dark apices (cf. Anthocoris nemoralis and Anthocoris confusus which have only antennal segment II pale at the base). The Anthocoris nemorum pronotum is black and the forewings are entirely reflective (this does not always show in photos). There is a dark patch on the wing membrane which is typically shaped like an hourglass. The legs are orange-brown often with a dark patch at the proximal end of each tibia, and a dark patch on each femur, especially on the hind legs.

Immature Anthocoris nemorum are brown or reddish brown - the third picture above shows an immature anthocorid.

Anthocoris nemorum is mainly found on low vegetation rather than trees, and is especially common on nettles (cf. Anthocoris nemoralis and Anthocoris confusus which are mainly found on trees). Anthocoris nemorum is an voracious predator of aphids and other small insects, and has been considered as a potential agent for biological control of aphids, for example of the damson-hop aphid (Phorodon humuli) and of the pear psyllid (Cacopsylla pyri). Anthocorids may also suck plant juices, but they cannot grow or reproduce on a purely plant diet. The species has a wide distribution stretching from Europe right across the Palearctic zone to China.

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Miridae (Mirid bugs)

Mirid bugs are small to medium-sized, rather delicate looking bugs, usually oval or elongate and very varied in colour. Like the anthocorids they have a piercing and sucking rostrum, but it has four rather than three segments. The forewings have both a cuneus and an embolium. The majority of the over 6000 species of mirid bugs live on plant juices and can be major agricultural pests. But a number of species supplement their vegetatian diet with insect or mite prey, and a few species are mainly predatory. We only cover the mirid species that are known to take aphids as part of their diet.

 

Atractotomus magnicornis

Atractotomus species are small black or dark red-brown bugs. The adults are characterized by having the dorsal surface covered in flattened golden or silver hairs, and by having the second antennal segment strongly thickened in one or both sexes. Atractotomus magnicornis has the first antennal segment approximately cylindrical (cf. Atractotomus mali which has the first antennal segment almost triangular and lives on hawthorn) (cf. Atractotomus parvulus which has a slightly shorter second antennal segment, and lives on Scots pine).

Atractomus magnicornis is zoophytophagous, feeding on Norway spruce (and less often on a wide range of other conifers) and preying on aphids and other small insects. We have also recorded it as man-biting. It is distributed throughout Europe.

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Atractotomus mali (Apple brown bug)

Atractotomus species are small black or dark red-brown bugs. They are characterised by having the dorsal surface covered in flattened golden or silver hairs, and by having the second antennal segment strongly thickened in one or both sexes. Adults of Atractotomus mali (see first picture below) have the first antennal segment almost triangular (cf Atractotomus magnicornis which has the first antennal segment approximately cylindrical and lives on Norway spruce) (cf. Atractotomus parvulus which has a slightly shorter second antennal segment, and lives on Scots Pine). Immature Atractotomus mali (see second picture below) are red, with the fore-parts darker.

Both pictures above copyright L. Skipper under a Creative Commons Attribution 4.0 International License.

Atractomus mali is zoophytophagous, feeding on hawthorn and apple, and preying on aphids and other small insects. It is distributed throughout Europe.

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Blepharidopterus angulatus (Black-kneed capsid)

Adults of Blepharidopterus angulatus are slender and parallel-sided blue-green capsids. They have black patches on the posterior angles of the pronotum and variable yellow marks on the scutellum and forewings. The length of the first antennal segment is roughly equal to the width of the head. They have black patches at the bases of the rather bristly tibiae, the 'black knees' in the English name.

Second image Copyright Skipper & Tolsgaard, Projekt Allearter, under a Creative Commons Attribution 4.0 International License

The black-kneed capsid is found on many deciduous trees. It is polyphagous - feeding on plant juices, aphids, mites, other small insects and aphid honeydew. The latter explains why they are often found searching the upper leaves of a plant when their prey is usually found on the undersides. It is found throughout Europe, the former USSR, North Africa and Canada.

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Deraecoris lutescens

Adult Deraeocoris lutescens (=Deraeocoris punctulatus) are usually orange-brown with blackish margins (see pictures below). The hemelytron membrane of Deraeocoris bugs has no hairs, but the remainder of the forewings have short fine hairs. The scutellum has two dark bars, and unlike the rest of the dorsal surface is unpunctured. The adult body length of males is 3.8-4.3 mm and of females 4.0-4.6 mm. The larvae are grey-green and covered with truncate black hairs.

First image, Copyright Entomart.Be, reproduced by permission.
Second image, Copyright C. Quintin, INPN reproduced, by permission, under a Creative Commons BY-NC-SA license.

Deraeocoris lutescens is zoophagous and phytophagous, predating small invertebrates including aphids, and also probing the leaves of trees and some herbaceous plants such as nettles. It occurs in southern Britain and central and southern Europe.

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Deraeocoris ruber (Red-spotted plant bug)

The adult Deraeocoris ruber is a rather wide medium sized bug. The dorsal surface is very shiny and varies in colour from red-orange to black (see pictures below showing variation from mainly red to mainly black). The first antennal segment and at least the base of the second are black. The body length of the adult ranges from 6-8 mm. Nymphs are crimson reddish with a characteristically wide abdomen bearing black spines.

Deraeocoris ruber is found on a variety of herbs, shrubs and trees. It especially likes the common nettle (Urtica dioica), which is where it was found in the first of the pictures above. It feeds on nettle, and is predatory on aphids and other small insects. The red-spotted plant bug is found throughout the holarctic region.

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Dicyphus pallidus.htm

Adults of Dicyphus pallidus may be brachypterous or macropterous. The head is pale with dark markings. The first antennal segment is reddish at the apex, rather than being strongly red throughout. The second antennal segment is at most slightly darkened at both ends, but not blackish. There are black bristles along the underside of the hind femur.

Note:
We initially mis-identified the specimens shown below as possible Dicyphus pallicornis, being unaware of the existence of Dicyphus pallidus in Britain.

As of mid December 2018, British Bugs had no page on Dicyphus pallidus, albeit Nau (2010) reports its occurrence there, and Dicyphus pallidus is included in their British Heteroptera checklist (2017). Also NBN had no record of it and, for reasons unexplained, gave its "accepted name" as Dicyphus epilobii.

Dicyphus pallidus is mainly found on hedge woundwort (Stachys sylvatica). However, Munch (2013) notes that it is also often found associated with Macrolophus rubi on blackberry (Rubus), and the pictured mirid was found on bramble (Rubus fruticosus).

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Dryophilocoris flavoquadrimaculatus

Adult Dryophilocoris flavoquadrimaculatus are always macropterous. The hemelytra are black with yellow markings. The posterior of the pronotum is strongly raised and the pronotum and forewings are covered with long fine erect hairs. The length of adult Dryophilocoris flavoquadrimaculatus is 6-7 mm.

Adults can be found in May and June, especially on oak. Dryophilocoris flavoquadrimaculatus feeds on oak, aphids, Diptera, insect eggs and other Heteroptera (Psallus and Orthotylus) (Encyclopedia of Life).

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Grypocoris stysi

Adults of Grypocoris stysi have a distinctive chequered pattern of light yellow-white areas and a more-or-less bright orange-yellow cuneus (see two pictures). The femora are blackish and the tibiae brown. Adult body length is 6-8 mm.

Grypocoris stysi is found on nettles in woodland and especially on umbellifers. The bugs feed both on flower heads and on small invertebrates such as aphids, for example see the second image above. It is distributed throughout Europe.

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Harpocera thoracica (Oak catkin mirid bug)

Adults of Harpocera thoracica are sexually dimorphic. Males (see first picture below) are more elongated, have longer tibiae and their second antennal segment is enlarged. The colour ranges from black, dark brown to orange to pale brown with the males usually darker than the females. The tips of the hemelytra are black, surrounded by white markings. The legs are brown or yellowish brown and the antennae are brown. Immatures are reddish and covered in dark hairs and with the two basal antennal segments thickened.

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Heterotoma planicornis

The adult of Heterotoma planicornis is black with very unusual broad and flattened antennae (see picture below) extending forward from the head. The pronotum and hemelytra are black, sparsely covered with a mixture of dark and pale hairs. The femora are green and the tibiae are yellowish brown. The male body length is 4.6-5.3 mm and the female body length is 4.9-5.5 mm. Immature Heterotoma planicornis are reddish in colour and also have an enlarged second antennal segment.

Heterotoma planicornis is zoophagous and phytophagous, feeding on various insects including psyllids and aphids, as well as spiders and mites, and numerous herbaceous plants and trees. Heterotoma planicornis is native to Europe, and has been introduced to the United States and New Zealand.

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Macrolophus pygmaeus.htm

Two species (Macrolophus pygmaeus and Macrolophus melanotoma) have been used for biological control in glasshouses, and several other related species (e.g. Macrolophus rubi) also occur in the wild. We give key characteristics for these species as well as for Macrolophus pygmaeus.

Adult Macrolophus species are green and have a dark bar between each of the eyes and the pronotum (see first picture below). Macrolophus pygmaeus has the third antennal segment only about 1.75 times as long as the fourth (cf. Macrolophus rubi which has the third antennal segment at least twice as long as the fourth). The clavus is entirely green (cf. Macrolophus rubi which has a clear black mark at the apex of the clavus). The adult has the first antennal segment black (cf. Macrolophus melanotoma, formerly Macrolophus caliginosus, which usually has a white central band on that segment). The immatures of Macrolophus pygmaeus (see second picture below) have the first antennal segment a greenish brown.

Note:
There is considerable confusion in the literature between Macrolophus pygmaeus and Macrolophus melanotoma because the colour pattern on the first antennal segment does not always reliably differentiate the two species (Perdikis et al., 2003). We know of no studies directly comparing the biocontrol potential of each species. Since it is not always possible to know to which species the publication refers, we have included both species in our literature review.

Both pictures above copyright Skipper & Tolsgaard (2013) under a Creative Commons Attribution 4.0 International License.

Macrolophus pygmaeus is zoophagous and phytophagous. Its plant host is hedge woundwort (Stachys sylvatica), where it feeds on plant juices. Its animal prey comprise a variety of small invertebrates including aphids, whitefly, leaf miners, moth eggs and spider mites. When used for biocontrol in tomato crops in greenhouses, the most recent research indicates that the predator provides both 'services' for biocontrol of key pests, and 'disservices' as it feeds on the reproductive organs of tomato plants, reducing yield.

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Miris striatus (Fine-streaked bugkin)

Adults of Miris striatus (see first picture below) have a cuneus that varies from yellow to orange-red, but is never black tipped (cf. Rhabdomiris striatellus, which has a black-tipped cuneus). The adult body length is 9-11 mm. The nymphs (second picture below) are ant-like with yellow markings and reddish brown legs.

First picture above copyright Fritz Geller-Grimm under a CC BY-SA 3.0 licence.

Miris striatus is usually found on oak or hawthorn and overwinters in the egg stage. It is reported to be largely predatory feeding on small insects such as aphids and the eggs and larvae of moths and beetles. It has also been recorded feeding on aphid honeydew (Wheeler, 2001).

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Phylus coryli

Adult Phylus bugs are fairly long and slender. Phylus coryli has forewings that vary from light brown to black, with the cuneus usually (but not always) slightly reddish. The head is black. (cf. Phylus palliceps which has red to yellow-red forewings and a yellow to pale brown head) (cf. Phylus melanocephalus which has yellow to orange-red forewings and a dark brown or black head). Adult length is 4.5-5.5 mm.

Phylus coryli is found on hazel (Corylus avellana), whilst the related species Phylus palliceps and Phylus melanocephalus are found on oak (Quercus). All three species are zoophagous and phytophagous. Phylus coryli is widespread in Europe through to the Caucasus, but it missing from parts of southern Europe.

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Plagiognathus arbustorum

The ground colour of adult Plagiognathus arbustorum varies from pale olive-green to light red-brown to almost black (see pictures), but the head and pronotum are usually dark. The dorsal surface of the thorax and forewings is covered in dark hairs. The green larvae can be distinguished when in the second and subsequent instars by the dark brown or black line on the front of the hind femora whilst the basal antennal segment is black; in the later instars additional dark markings are present.

Second image (dark form), Copyright S. Rae under a Creative Commons Attribution 2.0 Generic License

Plagiognathus arbustorum is known to be both a plant feeder, especially on nettles (Urtica dioica), and a predator of small insects. The eggs are laid in the autumn and hatch in the following May. It is found in North America, most of Europe, and east to Siberia and Central Asia.

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Psallus ambiguus

Psallus species are small mottled red, grey or dark brown bugs with the pronotum and forewings covered in scale like golden hairs and with the tibial spines arising from black spots. Psallus ambiguus is blackish-brown often with an orange-red suffusion over the cuneus (this seems to be especially the case in females). The first antennal segment is black; the second segment is black in males, but partly pale over the basal half in females; the third segment is pale in both sexes. It is one of the larger Psallus species with a body length of >4 mm.

Psallus ambiguus is found on a range of deciduous trees including apple (Malus), hawthorn (Crataegus), sallow (Salix) and alder (Alnus). It is distributed throughout Europe, and is common in many areas. It is both phytophagous and zoophagous, and the nymphs probably need animal food to grow.

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Psallus varians

Psallus species are small mottled red, grey or dark brown bugs with the pronotum and forewings covered in scale-like golden hairs and with the tibial spines arising from black spots. Adults of Psallus varians are difficult to separate from other Psallus species. Judging by the photos available of this species, they are often golden brown with an orange-red suffusion on the cuneus (see first picture below).

Psallus varians is one of the most common Psallus species on beech (Fagus), although it is usually considered to be an oak (Quercus) specialist. It is also found on willows (Salix), birches (Betula), whitebeams (Sorbus), hazels (Corylus), alders (Alnus) , and ash (Fraxinus). They feed both on tree pollen and aphids. There have been more cases of man-biting with Psallus varians than with many others. In Germany in the summer of 2016 there was a swarming phenomenon and many people were bitten. The 'sting' can be painful, and puncture wounds were said to be inflamed.

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Tupiocoris rhododendri (Rhododendron mirid)

Adults of Tupiocoris rhododendri have a distinctive white collar and dark pronotum. The first segment of the antennae is yellow, contrasting with the black second segment. The legs are yellow. The length of the adult is 4.0-5.0 mm.

Tupiocoris rhododendri is phytophagous and zoophagous. Its foodplant is restricted to Rhododendron, but it also feeds on aphids and other small insects. It overwinters in the egg stage, with adults present from June to early August. It is native to the Nearctic zone, but has been introduced to Europe.

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Nabidae (Damsel bugs, Nabid bugs)

Damsel bugs are small to medium-sized, slender bugs, usually light to dark brown or black with a four-segmented rostrum. The front femora are slightly enlarged and raptorial, being used to catch prey. There is a series of elongated cells around the front wing membrane. Some species are brachypterous (with reduced wings). Damsel bugs are often found in crops, where they are predacious on many types of soft bodied insects including aphids.

 

Himacerus apterus (Tree damsel bug)

The adult Himacerus apterus has rather short reddish-brown wings (see pictures below), not reaching beyond the 3rd or 4th abdominal segment (cf. the smaller Himacerus mirmicoides which has relatively longer wings extending over about three quarters of the abdomen). Himacerus apterus has a black connexivum with orange-red spots, clearly visible in both pictures below.

As its English name indicates, Himacerus apterus is a tree-dwelling species on deciduous and, less commonly, on coniferous trees. It feeds on mites and various small insects including aphids. The tree damsel bug is found in most of Europe, and southern and central Asia. There are also historical records of it in Nova Scotia.

 

Reduviidae (Assassin bugs, Reduvid bugs)

Assassin bugs range in length from 4 to 40 mm. They have a short 3-segmented rostrum which fits into a ridged groove in the prosternum. The rostrum is used primarily for stabbing the prey, but is also rasped against the ridges to produce sound by stridulation. The head is typically constricted behind the eyes, giving it a neck-like appearance. Unlike the damsel bugs, the forelegs are not raptorial. The antennae are long and thin and are not clubbed. Most species prey on other arthropods, but those in the subfamily Triatominae are blood suckers, and can transmit a serious disease. Many species can inflict a painful bite to humans.

 

Empicoris vagabundus (Common thread-legged assassin bug)

Empicoris bugs are called 'thread legged' bugs on account of their long thin legs. The best distinguishing character of the genus is the curved rostrum (see pictures below). The front legs are raptorial for catching prey. Empicoris vagabundus has pale sides of the connexivum which distinguishes it from the, more common, Empicoris culiciformis and the, less common, Empicoris baerensprungi. The species is relatively large compared to other members of the genus at a length of 6-7 mm.

Empicoris vagabundus is found on various deciduous and coniferous tree species, especially on dead leaves of those trees. It can also be found on lichens and webs of spiders, and of psocids, where it hunts and eats small Diptera and Homoptera including aphids. It is distributed throughout Europe.

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Acknowledgements

For the heteropteran bugs we have used Southwood & Leston (1959) and British Bugs to aid in identification and for the key characteristics.

For aphids 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 sp 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. (2006). Aphids on the world's herbaceous plants and shrubs. Vols 1 and 2. John Wiley & Sons.