Densities of beneficial arthropods within pear and apple orchards affected by distance from adjacent native habitat and association of natural enemies with extra-orchard host plants

Beneficial arthropods were sampled using beat trays in 10 pear and 8 apple orchards in Washington and Oregon, USA. One border of each orchard was adjacent to non-agricultural land (extra-orchard habitat). Beneficial arthropods were also sampled on 45 species of plants in extra-orchard habitats adjacent to study orchards. Orchard samples were taken monthly at 2 or 3 distances (depending upon size of the orchard) from the edge adjacent to extra-orchard habitat. An overall mean of 33.8 beneficial arthropods was taken per 26-tray sample (43.8% spiders; 37.8% predaceous insects; and 18.5% parasitoids). In May, July, and August, densities of beneficial arthropods declined significantly as distance from extra-orchard habitat increased. The decline was most evident in spiders and parasitoids; no trend was noted for predaceous insects. Most of the decline occurred between 0-60 and 60-120 m into the orchard, with no significant decline between 60-120 and 120+ m. These results are consistent with the idea that some taxa of beneficial arthropods moved into orchards from extra-orchard habitat. The most common predaceous insects in orchards were Miridae (32.3% of beneficial insects), Coccinellidae (11.1%), Chrysopidae (6.9%), and Hemerobiidae (5.7%). Important parasitoids were Trechnites insidiosus (7.6% of beneficial insects) and Pnigalio flavipes (2.3%). The families Linyphiidae, Salticidae, Oxyopidae, Philodromidae, Theridiidae, and Clubionidae together comprised 87.3% of total spiders. Twenty-two taxa of spiders and 22 taxa of beneficial insects collected in orchards were also collected on plant species outside of the orchards. The predatory insects Orius tristicolor, Deraeocoris brevis, and Nabis alternatus and the spiders Misumenops lepidus and Oxyopes scalaris were collected on the largest number of extra-orchard plant species. Common parasitoids of orchard pests were never collected from extra-orchard host plants.