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Leafcurl ash aphidOn this page: Identification & Distribution Other aphids on the same host Damage & Control
Life cycle, Identification & Distribution
Overwintering eggs of Prociphilus fraxinifolii hatch in April-May on ash (Fraxinus) before bud burst. The newly-emerged fundatrices feed on the buds. As leaves develop, these aphids begin to feed at leaf bases and stalks and bracts; as a result, leaves become gradually deformed until they are tightly curled and clumped to form 'leaf nests' (see first picture below). They are sometimes also discoloured to a red-brown colour. Inside the pseudogall feeds a colony of fundatrigeniae (see second picture below). Early-instar immature Prociphilus fraxinifolii are pale yellow, but later instar immatures and adults are a pale yellowish green (see third picture below). Many aphids are thickly coated in wax, secreted by large wax glands on the head and in three rows on the body. The wax has to be resecreted after each moult so recently moulted aphids have little wax. A crucial role of the secreted wax is to prevent these aphids becoming contaminated by their own honeydew (see second picture below of wax-coated honeydew droplets) and that of other members of the colony (see also for Eriosoma lanigerum).
Images above by permission, copyright Claude Pilon, all rights reserved.
The generation of fundatrigeniae includes both apterous and alate morphs (see pictures below). Characteristics of the alate can be used for identification purposes. Alatae of Prociphilus fraxinifolii have a yellow-green abdomen (cf. Prociphilus fraxini and Prociphilus bumeliae on ash, which are brown with green patches.) The base of antennal segment VI bears 1-5 irregularly-shaped secondary rhinaria, differing from those on antennal segment III (cf. Prociphilus fraxini and Prociphilus bumeliae on ash, which have no secondary rhinaria on the base of antennal segment VI).
Both images above by permission, copyright Claude Pilon, all rights reserved.
Some of these aphids may remain in leaf nests all summer, but from about July some viviparous females change their feeding sites to the roots of ash trees where they live and reproduce parthenogenetically.
Image above by permission, copyright Mark Brundrett, all rights reserved.
On the roots there is a symbiotic association betweeen the aphid and the fungus Boletrinellus merulioides. When feeding on the roots, Prociphilus fraxinifolii is enlosed by hollow structures (sclerotia) of the fungus. Brundrett & Kendrick (1987) suggest that in exchange for housing the aphid, the fungus receives nutrients excreted by the aphid in its honeydew. In autumn these root colonies produce alate sexuparae which return to the surface, and give birth to males and oviparous females, thus completing the annual life cycle. Remaining leafnest colonies also produce sexuparae in the autumn. Aphids which remain on the roots may reproduce parthenogenetically all-year-round on Fraxinus roots.
Prociphilus fraxinifolii is common and widely distributed in the USA, and is also found in Canada and Mexico. It has been introduced to Chile, South Africa and Europe, from where it has spread to Iran and Kazakhstan. It has also recently been reported from Beijing, China.
Other aphids on the same host
Prociphilus fraxinifolii has been recorded on 8 species of ash (Fraxinus americana, Fraxinus excelsior, Fraxinus latifolia, Fraxinus nigra, Fraxinus pennsylvanica, Fraxinus quadrangulata, Fraxinus uhdei, Fraxinus velutina).
Damage and control
Infested ash leaves curl, distort and drop prematurely. There can also be a problem with large amounts of honeydew produced by colonies of leafcurl ash aphid. This can be unsightly, but more importantly promotes the growth of dark sooty mould which can impair photosynthesis by the leaves. Root feeding on small nursery trees can also inhibit growth.
No control is needed in landscapes to protect the survival of otherwise healthy trees (see UC IPM). If control is imperative, then application of systemic insecticides is the only option.