Comparisons of Phytoseiid Predator Populations in Sprayed and Unsprayed Apple Orchards in Cache Valley, Utah

A comparative study of phytoseiid populations was made of two well-cultivated and regularly sprayed apple orchards with two unsprayed orchards in Cache Valley, northern Utah. Two phytoseiid species, Typhlodromus mcgregori Chant and T. occidentalis Nesbitt were observed on the apple leaves, under the bark, and occasionally in the litter and soil. Amblyseius cucumeris (Oudemans) occurred in the soil and litter and occasionally under bark. T. mcgregori was dominant in the unsprayed orchards, and T. occidentalis in the sprayed. Of the phytophagous mites, which served as food for the phytoseiids, the two-spotted mite, Tetranychus urticae Koch was dominant. Other phytophagous mites were the brown mite, Bryobia rubrioculus (Scheuten), the European red mite, Panonychus ulmi (Koch), and the McDaniel mite, Tetranychus mcdanieli McGregor. The study suggests T. mcgregori to be a non-specific, facultative predator of phytophagous mites. T. mcgregori was adversely affected by standard pesticide practices, but T. occidentalis survived in larger numbers. The phytoseiids seem well adjusted to the environment of the unsprayed orchards and to contribute to the low phytophagous mite populations in those orchards. In the sprayed orchards, the phytoseiids failed to control the high populations of phytophagous mites which developed. No statistical differences were found in the efficiencies of the mite brushing machine and Berlese funnels in removing either phytoseiid or phytophagous mites from apple leaves