Ecology of mites on pomaceous fruit trees and related wild hosts in Hood River Valley Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/jd473107d

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  • The ecological interrelationships of mites occurring in and near the Hood River Valley, Oregon, pome fruit orchards were investigated to determine the possibility of an integrated control program using the species already present. Survey sampling methods were used to study mites on wild hosts (Crataegus douglasii Lindl., Crataegus columbiana Howell, and Amelanchier florida Lindl.) related to pome fruits, abandoned and commercial apple and pear orchards, and soil with its cover in abandoned apple and pear orchards. Distribution of mites among the orchards, within the trees, upon the leaves, and among certain varieties was also investigated. Mites were collected from leaves, spurs and stems, bark, and soil and cover in the orchards; and from leaves, and spurs and stems of the wild hosts. Mites frequently collected from the wild hosts were Bryobia arborea Morgan and Anderson, Panonychus ulmi (Koch), Tydeus californicus (Banks), Tydeus zempoalensis Baker, Typhlodromus rhenanus (Oudms.), and Typhlodromus mcgregori Chant. Eotetranychus carpini (Ewing), Eotetranychus willamettei McG., Balaustium sp., Typhlodromus anachialus (Kennett), Typhlodromus arboreus (Chant), and Typhlodromus crataegi Jorgensen and Chant were collected less frequently. Crataegus columbiana was the preferred habitat for Tydeus californicus, whereas Tydeus zempoalensis preferred Crataegus douglasii. The nature of these preferences is unknown, since both species were apparently non-phytophagous. Pest species (Panonychus ulmi and Bryobia arborea) were abundant on wild host plots only when these were near orchards infested with the same pests. Wild hosts are not considered important sources of pests or predacious species far adjacent orchards at the present time. Forty-seven species of mites were collected from the soil and cover, of which only three (Tetranychus telarius (L), Balaustium sp., Typhlodromus rhenanus) were also abundant on the trees. Since the populations on the trees are apparently isolated from those on the soil and cover, it was concluded that the two populations are independent of each other. Only if pests, such as Tetranychus telarius and predators such as Balaustium sp., which migrate to and from the trees, become numerous in the orchards will the populations on the soil and cover interact directly with populations on the trees. Species which were associated with abandoned and semi-commercial orchards were Bryobia arborea, Panonychus ulmi, Eotetranychus carpini, Tetranychus telarius, Tydeus californicus, Tydeus zempoalensis, Balaustium sp., Mediolata mall, Typhlodromus mcgregori, Typhlodromus rhenanus, and several less abundant species. Mite complexes among the orchards varied markedly, resulting in rather diverse species associations in different orchards. This was particularly true with respect to the predators. Some predators (Typhlodromus rhenanus and Typhlodromus mcgregori) that were abundant in one orchard were virtually absent from others. Also, Tydeus californicus preferred abandoned pear orchards to apple, whereas Tydeus zempoalensis preferred apple. Distributions of predators were never well syncronized with those of the pests, especially Panonychus ulmi. This was true, regardless of what distribution was considered; seasonal, among the orchards, within the trees, upon the leaves, or between mature and immature leaves. As a result of these discrepancies, it was concluded that predation by Typhlodromus rhenanus, Typhlodromus mcgregori, Mediolata mali (Ewing), and Balaustium sp. was not efficient on Panonychus ulmi and Bryobia arborea; but, efficiency was probably higher on Eotetranychus carpini, Eotetranychus willamettei, and Tetranychus telarius. These same discrepancies probably resulted in the lack of interactions between predators and prey that could be identified as causative action on the part of the predators. Interactions between predators and prey were not sufficient to be interpreted as being caused by predation. The data obtained during this study led to the conclusion that the acarine predators now present would not be particularly beneficial in an integrated control program.
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