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Small downy birch aphidIdentification & Distribution Biology & Ecology Other aphids on the same host
Identification & Distribution:Betulaphis quadrituberculata apterae are pale yellowish green to pale yellow to almost white. In late summer to autumn they may have patches of yellow to orange pigment.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.
The alates 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 apterous with rather long antennae. oviparae 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.
Biology & Ecology:
Betulaphis quadrituberculata overwinters in the egg stage on birch trees. The eggs hatch in spring and the young nymphs feed on the undersides of the leaves developing into either winged or wingless fundatrices (Stroyan, 1977 ). Large numbers of mature alate fundatrices can be found in mid-May (see picture below) on the tips of birch leaves
In succeeding generations nearly all individuals are apterous and rather sedentary in habit. Aphids tend to be dispersed singly or in small groups, although they can reach high densities if conditions are suitable. Varty (1964) found a similar situation for Betulaphis quadrituberculata in New Brunswick, Canada and concluded that Betulaphis quadrituberculata mainly disperses by the flight activity of the fundatrices in spring.
Varty (1964) noted that the viviparae are seasonally polymorphic in size and colour. This mainly takes the form of darker yellow or orange patches on the dorsum, shown in the two photos below.
Durak & Wojciechowski (2008) found that Betulaphis quadrituberculata was eudominant with Calaphis betulicola in mixed coniferous forest in June. Generally one peak of occurrence was noted in the middle of June.
The pictures above show a braconid parasitoid about to parasitize Betulaphis quadrituberculata as well as some of the parasitized mummies. Stary & Havelka (2008) record parasitism of the related species Betulaphis brevipilosa by the braconid Aphidius aquilus in the Czech Republic. Baker (pers. comm.) also records Aphidius aquilus parasitizing Betulaphis quadrituberculata in Wales, so it seems likely that this is the parasitoid shown above.
The ovipara (shown below) has the posterior abdominal segments produced into an elongate ovipositor-like structure.
According to the Stroyan (1977) and others the ovipara has a pigmented dorsal sclerotic pattern, but this does not seems to be the case with this specimen. Males are dark and apterous.
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. Of those, only 18 species occur on silver birch (Betula pendula) and/or downy birch (Betula pubescens) in Europe.