Calaphis flava

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. Most secondary rhinaria on antennal segment III are placed towards the base of the segment (see second micrograph below) (cf. Calaphis betulicolawhich has them placed towards the middle of the segment). The siphunculi of Calaphis flava are entirely pale or rarely have slightly dusky tips (cf. Calaphis betulicola which has the apical halves of its siphunculi dark). 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).

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: