Woolly apple aphid - Life cycle

The woolly apple aphid, like many other of its aphid cousins, is capable of rapid development in summer and can complete a series of overlapping generations.This means that, after the early spring period, all stages of the insect are likely to be present at one time. The population is composed entirely of females which reproduce asexually (parthenogenetically), giving birth to live female young. The only exception to this occurs rarely. From February onwards each summer, a proportion of the females are winged and, in its area of origin in North America, these winged forms fly to elm trees. On arrival, they produce male and female wingless young. These sexuales develop to adult, mate and lay eggs which overwinter on elm. However, this cycle on elm has not been seen in New Zealand and the winged females on apple have been found to produce very few male and female offspring. Eggs have been rarely seen (and did not hatch) and the winged aphids do not therefore, contribute to growth or dispersal of woolly apple aphid populations.

The woolly apple aphid overwinters in New Zealand mainly as crawlers (first instar nymphs) in cracks and crevices on the bark of the trees. These are resistant to the cold and in a dormant (diapause) condition. Some older nymphs (and crawlers) may also overwinter on the roots, protected from the cold by being under ground. As temperatures warm in the spring, the overwintering crawlers complete their development to adult females and produce live young that begin dispersing to new feeding sites. Nymphs feeding on the roots may also provide a source of infestation for the development of above-ground colonies. Research in Nelson suggests that spring development of crawlers may begin as early as August with a generation completed in about six weeks. This shortens to about three weeks in summer. There may be as many as ten overlapping generations of wingless stages of woolly apple aphid each year depending on temperature, with fewer generations in southern areas. Winged aphids are produced between February and late April. Further information is available on the life history of woolly apple aphid.