Eriosoma lanigerum (Hausmann) Woolly Apple Aphid
Apterae on Pyroideae are purple, red or brown, covered with thick white flocculent wax (see influentialpoints.com/Gallery); BL 1.2-2.6 mm. On roots, trunk or branches, often causing deformation and cancer-like swellings of bark. It is a severe pest of apple (eg. Weber & Brown 1988), and may also be found on Cotoneaster and Pyracantha, and more rarely on Cydonia, Crataegus, Pyrus and Sorbus, but is not so injurious to these plants. Anholocyclic populations, sometimes with an apparently abortive sexual phase, occur on apple throughout the world, overwintering on the roots (see Blackman & Eastop 2000, p. 271). Alate sexuparae producing oviparae and males on apple are reported from various parts of the world, and eggs may be laid on apple leaves (e.g. Fotedar & Kapur 1943, Asante 1994, Sandanayaka & Bus 2005), but there is no firm evidence that these are capable of hatching, and it unlikely that fundatrices would be able to develop on apple and complete the holocycle.
Siciunguis decima Zhang & Qiao, described from apterae and alatae (sexuparae?) and causing heavy damage to apple in China (G. Zhang et al. 1999b) seems likely to be a synonym.
In North America, aphids of the E. lanigerum group induce leaf rosette galls on Ulmus americana, but there is still doubt about the relationship of these to apple-feeding populations. Smith (1985) successfully transferred alatae from such galls to apple. However, alatae indistinguishable from those of E. lanigerum were obtained from reddish pink leaf curls on U. alata, and these would not transfer to apple but successfully colonised Crataegus uniflora. Similar aphids occur in leaf-cluster galls on sterile elms in Australia (Fisk et al. 1992).
The ecology and natural enemies of E, lanigerum on apple were studied by Bouchard et al. (1984; Quebec, Canada), Gontijo et al. (2012; Washington, USA), Thakur et al. (1988; India) and von Kogler (1989; Germany). Aphelinus mali is a widespread specialised parasitoid (but Aphelinus gossypii, which parasitises a wide range of hosts including Aphis and Rhopalosiphum spp., have often been misidentified as A. mali). Lavandero et al. (2011) studied genetic variability in the aphid and its parasitoid in Chile, Timm et al. (2005) studied its genetic diversity in South Africa, and Zhou et al. (2015) analysed the genetic diversity and structure of the populations introduced into China. Ruiz-Montoya et al. (2015) studied morphometric and allozyme variation in populations collected on Pyracantha koidzumii in Mexico. A study of predation by earwigs was made by Mueller et al. (1988). Costa et al. (2014) compared performance parameters of four clones of E. lanigerum in Australia. Davidson (1913) made a detailed study of morphology and anatomy. M.Su et al. (2016) studied the distribution and functioning of the wax gland pores. The complete mitochondrial genome has been published (Y. Wang et al. 2016a). See Molinari (1986) for a general review. 2n=12.
