THE DYNAMICS OF APHIS-POMI DE-GEER (HOMOPTERA, APHIDIDAE) AND ITS PREDATOR, APHIDOLETES-APHIDIMYZA (RONDANI) (DIPTERA, CECIDOMYIIDAE), ON APPLE IN NOVA-SCOTIA

The dynamics of Aphis pomi De Geer (Homoptera: Aphididae) and its pred ator, Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae), were studied over two seasons in a commercial apple orchard in Nova Scotia. Aphid and predator population dynamics were very different in the two seasons. The most numerous predator in both years was A. aphidimyza. This predator was found in the earliest colonies sampled each season a nd was present throughout the growing season. In the year with relativ ely high aphid densities a single peak in aphid and predator density w as seen in mid-July, just prior to maximum predation rate. The predato r's numerical response resulted in delayed density dependence in preda tion rate. In the year of low aphid densities, predator and prey dynam ics appeared uncoupled, and a higher rate of colony turnover may have been caused by other predators such as mirids. Aphidoletes aphidimyza tended to aggregate oviposition in high-density aphid colonies, but th is aggregation resulted in predation that was only very weakly spatial ly density dependent.