DIRECT AND INDIRECT SPECIES INTERACTIONS INFLUENCING WITHIN-SEASON DYNAMICS OF APPLE RUST MITE, ACULUS-SCHLECHTENDALI (ACARI, ERIOPHYIDAE)

We conducted a series of path analyses to determine which direct and i ndirect species interactions were most important in determining the wi thin-season dynamics of apple rust mite (Aculus schlechtendali) (Eriop hyidae) in a series of Nova Scotian (Canada) apple orchards. Typhlodro mus pyri (Phytoseiidae) was usually more important than Zetzellia mali (Stigmaeidae) in the direct reduction of the apple rust mite populati on growth rate. When both predators contributed to lowering apple rust mite growth, ?: pyri acted earlier in the season than did Z. mali. Pr edation by T. pyri was not affected by plant quality (nitrogen content or cultivar), but predation by Z. mall was enhanced by high nitrogen levels and was influenced by cultivar. There was little evidence of di rect competition between Panonychus ulmi and apple rust mite in these orchards, possibly due to the low densities of P. ulmi. The indirect e ffects were generally smaller than the direct effects, but were occasi onally important. Apparent competition between P. ulmi and apple rust mite was observed at times in some orchards, more often mediated by Z. mali than by T. pyri. Interference between the predator species was o nly occasionally strong enough to affect apple rust mite population dy namics.