Seasonal abundance of woolly apple aphid, Eriosoma lanigerum (Hausmann) and its important natural enemies in Armidale, northern New South Wales
S.K. Asante, Department of Zoology, University of New England, Armidale, New South Wales 2351, Australia.
Present address: International Institute of Tropical Agriculture, PMB 5320, Ibadan, Oyo State, Nigeria.
Summary
Studies were conducted on the seasonal population changes of the woolly apple aphid, Eriosoma lanigerum (Hausmann) and its associated natural enemies in a 41-year-old apple orchard in Armidale, New South Wales, Australia. All the life stages of apterous virginoparae of E. lanigerum were found on the apple trees throughout the year. First instar nymphs comprised a high proportion of the total population (>40% of all life stages and >50% of nymphal stages) throughout the year. The proportion of first instar nymphs in the populations was found to increase during the cold months (May-July) each year.
The population density was found to fluctuate considerably from one season to the next over three consecutive years, with peak numbers occurring between February and May (late summer to mid-autumn) and the lowest level occurring during the winter (June to August). For the three consecutive years, large numbers of the alate morph appeared in the populations from February to April only, with the highest peak occurring in March. Under the cool climatic conditions in the Armidale area, E. lanigerum can complete 10-11 overlapping generations a year. The factors that appeared most important to fluctuations in E. lanigerum numbers were, temperature, parasitism by Aphelinus mali (Haldeman), the development of alate morph (i.e. emigration or dispersal), predation (by European earwigs, lacewings, coccinellid beetles and syrphid flies), rainfall and fungal disease.
Plant Protection Quarterly (1999) 14 (1) 16-23.