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"It has long been an axiom of mine that the little things are infinitely the most important" (Sherlock Holmes)

 

 

Identification & Distribution:

The apterae of Calaphis flava (see first picture below) are pale green or yellowish with dark tips to the antennal segments, femoral-tibial joints, tibial apices and tarsi. The antennae are longer than the body and curving. The siphunculi of Calaphis flava are entirely pale or rarely have slightly dusky tips (cf. Calaphis betulicola  which has dark tips to its siphunculi). The body length of adult apterae is 1.9-2.7 mm.

 

The Calaphis flava alate (see second picture above and first below) has the wing veins somewhat darkened (cf. Calaphis betulicola, which has wing veins strongly darkened). Most secondary rhinaria on antennal segment III are placed towards the base of the segment (see second picture below) (cf. Calaphis betulicola which has them placed towards the middle of the segment).

 

Calaphis flava favours small bushes of downy birch (Betula pubescens), but is also found on young growth of larger trees and of other birch species. Alate males and apterous oviparae can be found in autumn on various Betula species. It is widespread in Europe eastward in Asia to Siberia and has been introduced to South Africa, Australia and North America.

 

Biology & Ecology:

Life cycle

In Britain we have sometimes found Calaphis flava to be fairly common on downy birch, but it is generally less common than Euceraphis.  Baker (2012)   in a survey at Dundreggan in Scotland found Calaphis flava feeding in small numbers on young growth of Betula pubescens emerging from trunks. The picture below shows Calaphis flava feeding on the young growth of downy birch in West Sussex.

Baker noted that it is easily overlooked on trees harbouring abundant Euceraphis species, though its lemon yellow colour, cone shaped siphunculi and feeding position are good field characters. The colour is actually rather variable with some individuals greenish and colour matching perfectly with the birch leaves (see first picture below) whilst others are a deep yellow (see second picture below) .

 

Hajek (1986)   describes how aphid host preference was used to detect a previously unrecognized birch species in California. Silver birch (Betula pendula) is a popular ornamental tree in northern California, which frequently hosts populations of four leaf-feeding aphid species. Differential aphid species distribution on occasional birch trees led to the identification of downy birch (Betula pubescens) (note numerous small downy hairs on leaf and stems of downy birch in picture below) planted among Betula pendula.

Spring sampling demonstrated that Calaphis flava occurred predominantly on Betula pubescens while Betulaphis brevipilosa, Callipterinella calliptera,  and Euceraphis betulae  were more abundant on Betula pendula. Callipterinella calliptera and Euceraphis betulae were rarely found on Betula pubescens, whereas Calaphis flava populations constituted 22% of the aphid fauna on Betula pendula when trees of the two species were adjacent. Betula pubescens hosted a larger total aphid population as well as abundant leafhoppers. Honeydew presence on lower canopy leaves of both tree species was positively related with aphid density.

Nerg et al. (2008)   tested whether the ectomycorrhizal infection level (see picture below) of roots of Betula pendula affected performance of above-ground insect herbivores by increasing available plant biomass, by enhancing availability of nutrients, or by modifying concentration of defense compounds in birch foliage.

Mycorrhizal root tips (Amanita) by Ellen Larsson [CC BY 2.5 ], via Wikimedia Commons 

Insect performance was determined for a range of insects including the phloem-feeding Calaphis flava. Young silver birch had either natural ectomycorrhizal infection level (on average 24% of short roots), reduced infection level after fungicide treatment or enhanced infection level after inoculation with a fungus. The most pronounced effect of infection level was observed on the growth of plants; the stem growth decreased. The birch aphid Calaphis flava produced significantly fewer nymphs on birches with enhanced ectomycorrhizal infection levels than on controls.

 

Natural enemies

Durak & Wojciechowski (2008)   found Calaphis flava had very low dominance values in Betula pendula woodland as might be expected given its preference for Betula pubescens as a host. Kavallieratos et al. (2004)  recorded four parasitoids Aphidius aquilus, Praon flavinode, Trioxys betulae and Trioxys cirsii parasitizing Calaphis flava in southeastern Europe.

We have yet to find any parasitized Calaphis flava, but we have found orange midge eggs (Cecidomyiidae) laid on the aphids (see picture below).

These will hatch to give cecidomyiid (Aphidoletes ?) larvae which are voracious aphid predators. Most of the literature on cecidomyiid predators of aphids indicates that eggs are laid on surrounding vegetation (e.g. Lucas & Brodeur, 1999 ), but we have often found them laid on the aphids as well as on the substrate.

 

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 the 15 species on Betula pubescens, Baker (2015)  lists 14 as occurring in Britain: Betulaphis quadrituberculata,  Calaphis betulicola,  Calaphis flava, Callipterinella calliptera,  Callipterinella minutissima, Callipterinella tuberculata,  Clethrobius comes,  Euceraphis punctipennis,  Glyphina betulae,  Glyphina pseudoschrankiana,  Hamamelistes betulinus,  Monaphis antennata,  Stomaphis quercus  and Symydobius oblongus. 

Acknowledgements

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 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).

Useful weblinks 

References

  •  Baker, E.A. (2012). Aphids and their parasitoids at the Dundreggan estate. June 2012.

  •  Durak, R. & Wojciechowski, W. (2008). Structure and dynamics of aphid communities connected with trees in selected forest associations. Polish Journal of Entomology 77, 79-92. Full text 

  •  Hajek, A. (1986). Aphid host preference used to detect a previously unrecognized birch in California. Environ Entomol 15(3): 771-774. Abstract 

  •  Kavallieratos, N.G. et al. (2004). A survey of aphid parasitoids (Hymenoptera: Braconidae: Aphidiinae) of Southeastern Europe and their aphid-plant associations. Appl. Entomol. Zool. 39(3): 527563.  Full text 

  •  Lucas, E. & Brodeur, J. (2004). Oviposition site selection by the predatory midge Aphidoletes aphidimyza (Diptera: Cecidomyiidae). Environmental Ecology 28(4): 622-627. Full text 

  •  Nerg, A.M. et al. (2008). The significance of ectomycorrhizas in chemical quality of silver birch foliage and above-ground insect herbivore performance. Journal of Chemical Ecology 34(10), 1322-1330. Abstract