GENETIC DIVERSITY OF AN INTRODUCED PEST, THE GREEN SPRUCE APHID ELATOBIUM-ABIETINUM (HEMIPTERA, APHIDIDAE) IN NEW-ZEALAND AND THE UNITED-KINGDOM

The green spruce aphid Elatobium abietinum (Walker) is an introduced p est in the United Kingdom and more recently in New Zealand. In outbrea k years this aphid can cause severe defoliation and sometimes death of spruce trees (Picea spp.). As chemical control is not financially via ble, other options including host-plant resistance and biological cont rol are currently being investigated. An understanding of the genetic variation of this pest is imperative in fully utilizing these control strategies. To examine this, E. abietinum was collected from Sitka spr uce Picea sitchensis from four locations in the UK that were up to 240 km apart. Of these, 40 aphids were analysed via two alternative polym erase chain reaction (PCR) analyses using primer pairs. The first anal ysis used 10-mer random primers, whilst the second analysis used prime rs designed to amplify across the intergenic spacer region of rDNA. Co mbining results from the two analyses allowed the 40 UK aphids to be s eparated into 28 different genotypes. The genetic variation was also h igh within each UK site, with 77 to 89% of the aphids sampled being of a different genotype. The two PCR analyses were subsequently used to examine 40 aphids across six sites in New Zealand up to 1200 km apart. No genetic variation was identified. Further analysis of several of t hese New Zealand aphids with 87 individual 10-mer primers and two poly merase enzymes, still did not detect any genetic variation. The high d egree of genotypic diversity in the UK populations was presumably due to a longer period of establishment, multiple introductions and/or sex ual reproduction. The contrasting lack of genetic variation in New Zea land populations was probably due to a very limited founder population , continued isolation and lack of sexual reproduction. Reduced genetic diversity can seriously decrease the ability of a population to adapt to control strategies. Therefore the durability of certain control me thods may be more readily maintained in such an isolated population in New Zealand.