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Lachnus are medium to large long-legged aphids with prominent siphuncular cones. The antennae are usually quite short - for apterae about half the body length. The cauda and anal plate are rounded. The alatae usually have pigmented wings - hence the English name 'variegated aphids'.
The Lachnus genus includes about 22 species, which mainly feed on the twigs and branches of broadleaved trees especially Fagaceae (oaks and beeches). They are nearly always attended by ants.
Lachnus longirostris (Scarce variegated oak aphid)
Apterae of Lachnus longirostris are shining dark reddish to blackish brown (see first picture below). The antennae are 0.4 - 0.5 times the body length. The abdominal dorsum is densely haired with long, fine-pointed hairs (cf. Lachnus roboris which only has a few short hairs on the dorsum). The middle parts of the hind tibiae are pale (cf. Lachnus roboris which has the hind tibiae pale at the base, but progressively darker over most of their length). In addition the hind tibia has very long and fine hairs on the ventral side of the distal part of hind tibia, greatly exceeding the width of the tibia. The siphuncular cones are rather small. The body length is 2.4 - 5.0 mm.
Lachnus longirostris alatae (see second picture above) have a pattern of forewing pigmentation similar to Lachnus roboris, but with the clear area between Rs and media extending to meet the media.
Scarce variegated oak aphids are found on twigs and branches of oak (Quercus species). Lachnus longirostris is widely distributed in Europe.
Lachnus pallipes (Variegated beech aphid)
Apterae of Lachnus pallipes are shining dark reddish to blackish brown. The antennae are 0.4-0.5 times the body length. The abdominal dorsum is densely haired (cf. Lachnus roboris which only has a few short hairs on the dorsum). The middle parts of the tibiae are pale (cf. Lachnus roboris which has the hind tibiae pale at the base, but progressively darker over most of their length). The siphuncular plates are relatively pale. The body length of the adult Lachnus pallipes aptera is 3.0-5.0 mm.
Lachnus pallipes alatae have a pattern of forewing pigmentation similar to Lachnus roboris, but with the clear area between Rs and media extending to almost meet the media.
Variegated beech aphids are found on two-year-old or older branches and stems of beech (Fagus sylvatica). They may also feed in ant shelters on roots of beech in summer. The variegated beech aphid is found over most of Europe south to Bulgaria and east to Russia and (apparently) the Far East.
Lachnus roboris (Variegated oak aphid)Lachnus roboris apterae are shining blackish brown. The antennae are quite short - for apterae 0.4-0.5 times the body length. The dorsum has only a few short hairs (cf. Lachnus longirostris & Lachnus pallipes which have the abdominal dorsum densely haired with long, fine-pointed hairs). There are two conical tubercles on the front of the mesosternum. The siphuncular cones are large and dark, with their maximum diameter exceeding the length of the second hind tarsal segment (cf. Lachnus pallipes & Lachnus longirostris which have smaller paler siphuncular cones with their maximum diameter less than the length of the second hind tarsal segment). The body length of an adult Lachnus roboris aptera is 2.5-5.5 mm.
Lachnus roboris alates have the forewing membrane pigmented except for four clear patches (hence the common name 'variegated' oak aphid). The clear area between Rs and media vein (M) only extends half way to the media (cf. Lachnus longorostris where the the clear area between Rs and media extends to almost meet the media.)
The taxonomy of Lachnus roboris is rather uncertain and Blackman & Eastop (1994) suggest that it is a complex of species with different karyotypes and host plants. In which case the species found on Castanea may be a different species. However, Dixon & Thieme (2007) record Lachnus roboris as feeding on either Quercus or Castanea.
Variegated oak aphids are found on twigs and small branches of oak (Quercus sp.) and sometimes sweet chestnut (Castanea sativa). Lachnus roboris do not host alternate. Apterous oviparae and large alate males occur in September-October and produce eggs which overwinter. They are present in Europe, the Mediterranean region and parts of the Middle East.