TRITROPHIC ASSOCIATIONS BETWEEN SPIDER WASPS (HYMENOPTERA, POMPILIDAE), WOLF SPIDERS (ARANEAE, LYCOSIDAE), AND GRASSHOPPERS (ORTHOPTERA, ACRIDIDAE) ON MIXED-GRASS PRAIRIE

Tritrophic associations between spider wasps, spiders, and grasshopper s were studied at 28 mixedgrass prairie sites in northwestern South Da kota. The multivariate ordination technique, detrended correspondence analysis (DCA), and correlation analysis were used to assess spatial c hange in the community structure of spider wasps collected with malais e traps and to define underlying ecological gradients associated with community change. Results indicated that community composition of spid er wasps changed along gradients defined partly by activity of the gro und-dwelling lycosid, Schizocosa mccooki (Montgomery), and percentage of sand in soils. Distinct habitat segregation was found for two of th e three dominant species of spider wasps, Cryptocheilus attenuatum Ban ks and C. terminatum (Say). Factor analysis of species at three trophi c levels indicated associations between numbers of the spider wasp Pom pilus apicatus Provancher, S. mccooki, and the obligate grass-feeding grasshopper Trachyrhachys kiowa (Thomas). All three species were abund ant in habitats with high grass coverage.