DISTRIBUTION OF METASEIULUS OCCIDENTALIS (NESBITT) AND TYPHLODROMUS PYRI SCHEUTEN (PARASITIFORMES: PHYTOSEIIDAE) IN APPLE ORCHARDS OF THE HOOD RIVER VALLEY, OREGON

In a survey of predaceous phytoseiid mites from 65 apple blocks in the Hood River Valley, Oregon, Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Scheuten were the principal species present. Metaseiulus occidentalis predominated over T. pyri by a ratio of about 2:1 in 1984 mites collected during 1985. In experimental, commercial, and integrated pest management blocks, M. occidentalis was present alone or predominated over T. pyri in up to 88% of the blocks, whereas T. pyri occurred alone or predominated in up to 20% of the blocks. Both species occurred in near equal proportions in a maximum of 20% of blocks. An analysis of nine factors influencing the relative abundance of M. occidentalis and T. pyri indicated that vegetation in the habitat surrounding the block and the pesticides used were most important. In 1986, seasonal distributions and proportions of predatory mites found in individual blocks were similar to those found in 1985. The feasibility of managing mixed populations of T. pyri and M. occidentalis in Hood River orchards is discussed.