RECOMMENDATIONS ON MINIMUM EXPERIMENTAL PLOT SIZE AND SUCCESSION OF APHIDOPHAGA IN WEST-VIRGINIA, USA, APPLE ORCHARDS

Five apple orchards in West Virginia, USA, were mana ed with five diff erent pest management practices ranging from unsprayed to conventional insecticides. Data were collected on aphid, predaceous insect, and sp ider abundance every 2 weeks from May to July along one or two randoml y selected, 15 consecutive tree transects. A total of 892 individual p redaceous insects was observed: 32% were Aphidoletes aphidimyza, 21% w ere Coccinella septempunctata and the rest were from 13 other taxa. Th e most important aphid predator seemed to be C. septempunctata. Of the 32 sample transects with predators, 72 % showed an edge effect in whi ch either the standard error or mean of predator abundance differed fr om the edge towards the center of the orchard. This edge effect extend ed a mean of 7 trees (30 m) into the orchard. Only 39% of the 33 trans ects that had spiders showed an edge effect, extending into the orchar d a mean of 8 trees (33 m). However, 75% of the transects with more th an one spider per tree had an edge effect of 10 trees (43 m). We recom mend a minimum border of seven trees before sampling for aphid predato rs and 10 trees before sampling for spiders. A recommended experimenta l plot size, for semi-dwarf, free-standing apple orchards, to eliminat e edge effects is 1.25 ha for aphidophaga, 1.5 ha for spiders; a minim um plot size of 0.6 ha for aphidophaga and 0.75 ha for spiders would m inimize edge effects.