INTRASPECIFIC AND INTERSPECIFIC PREDATION BY ADULT FEMALE METASEIULUS-OCCIDENTALIS AND TYPHLODROMUS-PYRI (ACARI, PHYTOSEIIDAE) WHEN PROVISIONED WITH VARYING DENSITIES AND RATIOS OF TETRANYCHUS-URTICAE (ACARI, TETRANYCHIDAE) AND PHYTOSEIID LARVAE

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodrom us pyri Schueten are used together and alone as biological control age nts against tetranychid pest mites of apple. Their effectiveness as co ntrol agents may be impacted by intraguild predation. The effects of p rey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated thr ough a series of experiments. Adult female predators were given prey a s mixed populations of phytoseiid larvae and larvae of a more preferre d species, the spider mite, Tetranychus urticae Koch, at different den sities and ratios. Typhlodromus pyri, more of a generalist predator, s howed higher rates of predation and cannibalism on phytoseiid immature s at most prey densities and ratios. Manly preference indices indicate d that T. pyri switched to feed on phytoseiid larvae at higher prey le vels and ratios of T. urticae than M. occidentalis. This greater abili ty to use phytoseiid larvae as prey may help stabilize T. pyri populat ions when more preferred prey is unavailable. This may, in part, expla in the observed persistence of T. pyri populations when M. occidentali s populations were decreasing in orchard test plots.