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Birch blister aphidOn this page: Identification & Distribution Biology & Ecology A social aphid? Other aphids on the same host
Identification & Distribution:
Hamamelistes betulinus wingless females are greenish or dark brown to black (see first picture below after wax removal). They are normally covered in white wax and live in yellowish blister-like pseudogalls on birch (see second picture below). They have short, 3- or 4-segmented antennae. In European populations, they lack siphuncular pores, although siphunculi are present in some generations in Japan. The body length of Hamamelistes betulinus apterae is about 1.5 mm.
Winged females have 5-segmented antennae and pigmented siphuncular pores. The body length of Hamamelistes betulinus alates is 1.3-2.0 mm.
In Japan, there is host alternation. The primary host is Hamamelis japonica, where sexual forms develop and eggs are laid on twigs and trunks. These hatch the following year and the developing fundatrices induce coral-like galls to develop from flower buds. Winged forms then migrate to birch. In Europe and northern Asia, the sexual stage on the primary host is lost, the aphid stays all year on birch. It feeds on the undersides of birch leaves, mainly silver birch (Betula pendula), causing pale yellowish blisters to develop on the upper surfaces. Hamamelistes betulinus overwinters as first instar larvae on the twigs.
Biology & Ecology:
Hamamelistes betulinus is not a common aphid in Britain, and we have so far found it only once - on Betula pendula at Oaken Wood in Surrey.
When disturbed they all put the rear ends in the air (the 'bums-up' posture), exuding honeydew (see picture below). They have no siphunculi, so could the honeydew contain some sort of alarm pheromone?
A social aphid?
The Hormaphidini is one of only six aphid tribes which have species known to be social. The most widespread feature of aphid sociality is the presence of soldiers to defend the clone against predators and/or to carry out cleaning in the gall and repair damage (Pike & Foster, 2008). These are commonly first-instar nymphs, but some use later instars. The commonest weapons are highly sclerotized stylets, legs and horns. Hamamelistes betulinus appears to produce partially sclerotized first-instar nymphs with strengthened legs (see pictures below, dorsal and ventral).
Defensive/cleaning behaviour has not yet been reported for first instar Hamamelistes betulinus, but is recorded for first instar Hamamelistes kagamii in the gall on the primary host (Shibao et al., 2010). We have not so far been able to observe the behaviour of Hamamelistes betulinus on Betula, but hope soon to be able to do so.
Other aphids on same host:
Blackman & Eastop list about 72 species of aphids as feeding on birches worldwide, and provides formal identification keys for aphids on Betula.