These are small, rather flat oval aphids. Adult viviparae may be winged or wingless. They have short 6-segmented antennae, with the terminal process about as long as the base of the last antennal segment. The cauda is short and conical and the anal plate is bilobed. Oviparae have dark dorsal markings and the posterior abdomen is extended as an egg-laying organ. Males are wingless with extensive dark dorsal markings.
A genus of 6 or 7 species rather evenly distributed through the holarctic usually feeding on the undersides of birch (Betula spp.) leaves. They have a sexual stage in their life cycle but do not host alternate and are not attended by ants.
Betulaphis quadrituberculataapterae are pale yellowish green, to pale yellow, to almost white. In autumn they may have patches of darker pigment. The antennae are shorter than the body (cf. Calaphis flava which is often found on the same leaves, and has antennae longer than the body). All dorsal body hairs of the apterae are usually long and capitate, although there are forms with hairs on abdominal tergites 1-4 much shorter (cf. Calaphis flava which has short, and inconspicuous, spinal and pleural hairs). The siphunculi are smooth truncate conical with a strongly flared apical rim. The cauda is broadly rounded and subtriangular, projecting slightly beyond the deeply cleft subanal plate. The body length of Betulaphis quadrituberculata apterae is 1.5-2.0 mm.
AlateBetulaphis quadrituberculata are broadly similar to the apterae, but the dorsal hairs are nearly all fine and acute, not capitate unless on abdominal tergite 8. Antennal segment III has a single row of 8-21 transverse, oval, distinctly fringed secondary rhinaria. Males are dark and apterous with rather long antennae. Oviparae have a pigmented dorsal sclerotic pattern, and have the posterior abdominal segments produced into an elongate ovipositor-like structure.
They are mainly found on the undersides of leaves of downy birch (Betula pubescens), but they also occur on silver birch (Betula pendula) and occasionally on grey alder (Alnus incana). Betulaphis quadrituberculata is widely distributed across Europe through Asia to China, and has been introduced to North America.
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).