Phenology, population ecology, and rarity of the New Zealand ribbonwood aphid, Paradoxaphis plagianthi

Abstract

We measured some aspects of the population ecology of an arboreal aphid, Paradoxaphis plagianthi, that might contribute to its rarity. Models were fitted to data on the development rate and variability of solitary aphids in the laboratory, from larviposition to maturity, which were similar to those of several common European tree‐dwelling aphids. Life tables suggested that the intrinsic rate of population increase increases linearly with temperature to a maximum of 0.123/day at 20°C. Aphid colonies raised in controlled environments showed a lower rate of increase, presumably due to crowding effects. The rate of increase of field colonies was further depressed, probably reflecting the action of other background mortality factors. New data for seasonal population trends in the field matched previously published results, showing an increase in spring followed by a rapid decline and low summer populations. A caging experiment failed to detect any differences in host suitability in late spring between Plagianthus regius, the main host, and Hoheria angustifolia or Parsonsia heterophylla, which may act as “spill‐over” hosts in some circumstances. While the results do not explain the rarity of P. plagianthi, they suggest new hypotheses to target future work.