Insects as indicators of land use in three ecoregions in the prairie pothole region

We sampled populations of insects in the prairie pothole region of North Dakota, USA, to determine whether relationships existed between community- or taxon-level indicators and 11 land-use types. Our goal was to determine if agricultural impacts were reflected in measurable differences for insect indicators: abundance, taxa richness, and diversity. Insects were sampled with light traps at 126 wetland basins in three ecoregions. Sampling was conducted three times each year during the spring and early summer of 1995 and 1996. Sites were selected based on the proportion of cropland to grassland, hayland, and Conservation Reserve Program land surrounding wetland basins at 50 and 400 m radii. Other landuse types included in our analyses were woodland, roadways, and five wetland types: permanent, semipermanent, seasonal, temporary, and riverine. In both years, tars richness, abundance, and diversity were greater for the second (June) and third (July) sampling periods than for the first period (May), and indicators were greater in the Drift Plain and Red River Valley ecoregions than in the Missouri Coteau ecoregion. Our analyses indicated several significant associations between insect indicators and land-use types; however, r(2) values were generally low. Much more of the variance in insect measures was explained by temperature, seasonal, and ecoregion effects. Several associations were significant within individual ecoregions (i.e., abundance of aquatic insects, Caenidae, Scarabaeidae, and Lepidoptera and number of Ephemeroptera families). However, no indicators were found in common for all three ecoregions. Several significant associations with land use were identified across all sites (i.e., all ecoregions combined). A small number of the significant relationships found across all sites were related to agricultural land use, and several indicated a negative relationship with grasslands. However, we observed several positive relationships between our insect indicators and riverine wetlands across sites and in the Red River Valley ecoregion for both years and spatial scales (i.e., the abundance of Caenidae, Scarabaeidae, Ceratopogonidae, Hydropsychidae, and Hydroptilidae).