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Alder buckthorn - willowherb aphidIdentification & Distribution Biology & Ecology Damage & Control
Identification & Distribution:Aphis frangulae apterae are generally dark green or blue-green, sometimes mottled (see pictures of apterae on the primary and secondary hosts below). Their abdominal sclerotic pattern is variable - it is usually confined to abdominal tergites 6-8 in smaller apterae, but broken bands are present in larger adults. The siphunculi are dusky or dark and are 0.85-2.16 times the length of the pale or dusky cauda. The body length of Aphis frangulae apterae is 0.9-2.4 mm.
In Europe the nominate subspecies of the alder buckthorn aphid (Aphis frangulae frangulae) host alternates between alder buckthorn (Rhamnus frangula = Frangula alnus) as the primary host and rosebay willowherb (Epilobium angustifolium) as the secondary host. Additional secondary hosts are shepherd's purse (Capsella bursa-pastoris) and yellow loosestrife (Lysimachia vulgaris). A different subspecies, Aphis frangulae beccabungae, host alternates from the same primary host to speedwell (Veronica beccabungae), as well as potato (Solanum tuberosum) and various Lamiaceae.
Aphis frangulae testacea (only found in Germany) is monoecious on alder buckthorn. Outside Europe populations can usually only be identified Aphis frangulae group. Sexual forms occur in autumn. The closely related Aphis gossypii (cotton or cucumber aphid) is a cosmopolitan polyphagous pest of warm climates, and is a greenhouse pest in cooler climates.
Biology & Ecology:
Until recently Aphis frangulae/gossypii was regarded as a cryptic group with uncertain separation between frangulae and gossypii. The two taxa were usually differentiated on the basis of life cycle and host plant. The work of Cocuzza et al.(2009a,b) and Carletto et al. (2009) has clarified the genetic separation between the two species in Europe. Aphis frangulae is fairly easy to find on its primary host, alder buckthorn, where it commonly feeds on young leaves alongside the main vein or on young shoots (see pictures below). Young shoots are often crumpled or distorted by the feeding aphids.
The colour varies greatly, mainly different shades of green, but also orange-brown and greenish-black.
Although there is little mention of it in the literature, we have usually found Aphis frangulae on the primary host to be ant attended. The picture below shows Aphis frangulae feeding on alder buckthorn attended by Lasius niger.
The picture below shows Aphis frangulae feeding on alder buckthorn attended by a Myrmica species.
We have yet to find Aphis frangulae frangulae on either potato or its main secondary host, rosebay willowherb, but we have found the other subspecies, Aphis frangulae beccabungae, on germander speedwell (Veronica chamaedrys) (see pictures below).
There are several postulate species of the Aphis frangulae group living on Lamiceae, namely Aphis lamiorum on Lamium species, Aphis stachydis on Stachys species, and Aphis symphyti on comfrey (Symphytum officinale). Cocuzza & Cavalieri (2014) have suggested that these should be synonomized with Aphis frangulae, although this may be premature given their different life cycles.
Damage and controlAphis frangulae beccabungae may cause feeding damage to potatoes, and is also an important potato virus vector, transmitting potato virus Y and potato virus M. Kostiw (2009) reports on the abundance and species composition of aphids on potatoes in Poland from 1970-2005. The number of alates trapped in yellow dishes over this period declined markedly in all sampling sites. The authors attributed this decline to a decrease in the land area cropped for potatoes which by 2005 was only one fifth of the area cropped in 1970.