Population patterns of Paradoxaphis plagianthi, a rare New Zealand aphid

In the first quantitative study of an endemic New Zealand aphid, the only known field populations of the rare Paradoxaphis plagianthiwere monitored for two years from 1999 to 2001. The species appears to be anholocyclic, persisting viviparously throughout the year on its deciduous host tree, the lowland ribbonwood (Plagianthus regius). Local aphid abundance increased rapidly in spring as new leaves appeared, but collapsed abruptly in November, probably due to dispersal and a decline in resource quality. Numbers then remained low until leaf senescence in late autumn, when they increased again to a smaller Peak. Aphids persisted on plump terminal buds for the short time in winter when host trees were completely leafless. Though several colonization events were observed in late spring, these were generally unsuccessful in establishing new populations, and local colony extinction was common. The apparent rarity of P. plagianthi suggests it could be threatened by introduced predators and competitors, or climate change.