S14 - Session P5 - Identification of biotypes of the woolly apple aphid (Eriosoma lanigerum) in the United Kingdom

Authors: Cindayniah Godfrey *, Michelle Fountain, Felicidad Fernández Fernández, Tom Pope, Simon Segar

The woolly apple aphid ( Eriosoma lanigerum Hausmann; WAA) originates in North America but has spread throughout apple growing regions around the world. In its host range WAA exhibits a heteroecious lifecycle, alternating between cultivated apple ( Malus domestica Borkh.) where it clonally reproduces, and American Elm ( Ulmus americana L.) for its sexual phase. Outside of this range it appears to have lost sexual reproduction, living entirely on apple. Woolly apple aphid reproduction is therefore thought to be predominantly, if not entirely, asexual, which is expected to lead to reduced genetic diversity. Both male and female sexuales have been captured although in all cases any eggs produced were not viable under laboratory conditions. Woolly apple aphid samples collected from the UK, USA and New Zealand were analysed using eight microsatellite markers (mean individuals per population = 8.8), and the elm balloon-gall aphid ( Eriosoma lanuginosum Hartig) was included as an outgroup. Assuming asexual reproduction of WAA outside of the USA and single colonization events for each country, four distinct genetic populations of WAA were expected with little variation within populations. Analysis with STRUCTURE software tested between one and seventeen putative populations and found the most likely number of populations to be thirteen although a further Principal Component Analysis (PCA) suggested a lower number of clusters, approximately four. This alone is not evidence of functional sexual reproduction but suggests the potential for previously unexpected geneflow between WAA populations in UK orchards, confirmed by the identification of twenty-two private alleles. This is a concern for pest control because of the potential for spreading genes which confer the ability to feed on resistant rootstocks, as has been reported in several apple-growing regions. The use of resistant rootstocks is a cornerstone of an effective Integrated Pest Management strategy of WAA and relies upon durably resistant plant material.