Abundance of Coccinellids and Their Potential Prey in Field-Crop and Grass Habitats in Eastern South Dakota

A rich fauna of coccinellids occurs in eastern South Dakota, but the abundance of some species has declined in association with the establishment of an exotic lady beetle, Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), in the mid-1980s. In this study, coccinellids were sampled within field-crop and grass habitats in eastern South Dakota from 1990 to 1995 to survey for various coccinellid species and to determine any effects of habitat management on abundance. Field crops (maize, wheat-alfalfa intercrop, and alfalfa) were subjected to high, intermediate, or low crop-management intensity (CMI), and grass habitats were managed for stands of warm season, cool season, or mixed species. A total of 1,306 adult and 155 larval coccinellids were collected. Four native species (Coleomegilla maculate (DeGeer), Hippodamia convergens Guerin Meneville, Hippodamia parenthesis (Say), andHippodamia tredecimpunctata tibialis (Say)) and C. septempunctata comprised over 96 percent of all coccinellids collected. Of declining species, four Coccinella transversoguttata richardsoni Brown were collected from alfalfa, but Coccinella novemnotata Herbst and Adalia bipunctata (L.) were not found during the study. Coccinellid abundance was seldom affected by CMI. Coccinellids were more abundant in wheat-alfalfa in 1995 under high than low CMI. Coccinellid abundance in maize and alfalfa did not differ with CMI. A prey species, Empoasca fabae (Harris) (Heteroptera: Auchenorryncha: Cicadellidae), was more abundant in alfalfa in 1995 under high and intermediate than under low CMI. Coccinellid abundance was not correlated with that of E. fabae in 1995, and showed inconsistent association with E. fabae during the study. In grass, adult coccinellids (total across species), adult H. tredecimpunctata tibialis, and aphids were more abundant in warm- season grasses than in cool-season or mixed grass stands in one of three years. Our results provide further evidence that C. septempunctata has become relatively abundant in eastern South Dakota, whereas C. transversoguttata richardsoni, C. novemnotata, and A. bipunctata have become rare or absent

Abundance of Coccinellids and Their Potential Prey in Field-Crop and Grass Habitats in Eastern South Dakota

A rich fauna of coccinellids occurs in eastern South Dakota, but the abundance of some species has declined in association with the establishment of an exotic lady beetle, Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), in the mid-1980s. In this study, coccinellids were sampled within field-crop and grass habitats in eastern South Dakota from 1990 to 1995 to survey for various coccinellid species and to determine any effects of habitat management on abundance. Field crops (maize, wheat-alfalfa intercrop, and alfalfa) were subjected to high, intermediate, or low crop-management intensity (CMI), and grass habitats were managed for stands of warm season, cool season, or mixed species. A total of 1,306 adult and 155 larval coccinellids were collected. Four native species (Coleomegilla maculate (DeGeer), Hippodamia convergens Guerin Meneville, Hippodamia parenthesis (Say), andHippodamia tredecimpunctata tibialis (Say)) and C. septempunctata comprised over 96 percent of all coccinellids collected. Of declining species, four Coccinella transversoguttata richardsoni Brown were collected from alfalfa, but Coccinella novemnotata Herbst and Adalia bipunctata (L.) were not found during the study. Coccinellid abundance was seldom affected by CMI. Coccinellids were more abundant in wheat-alfalfa in 1995 under high than low CMI. Coccinellid abundance in maize and alfalfa did not differ with CMI. A prey species, Empoasca fabae (Harris) (Heteroptera: Auchenorryncha: Cicadellidae), was more abundant in alfalfa in 1995 under high and intermediate than under low CMI. Coccinellid abundance was not correlated with that of E. fabae in 1995, and showed inconsistent association with E. fabae during the study. In grass, adult coccinellids (total across species), adult H. tredecimpunctata tibialis, and aphids were more abundant in warm- season grasses than in cool-season or mixed grass stands in one of three years. Our results provide further evidence that C. septempunctata has become relatively abundant in eastern South Dakota, whereas C. transversoguttata richardsoni, C. novemnotata, and A. bipunctata have become rare or absent

Diversity and Dominant Species of Ground Beetle Assemblages (Coleoptera: Carabidae) in Crop Rotation and Chemical Input Systems for the Northern Great Plains

Dominant carabid species present in crops and crop rotation sequences commonly used in the northern Great Plains were assessed as an initial step toward the management of carabids as natural control agents. Ground beetle populations were determined by pitfall trapping in 4 crop rotation treatments maintained under high, managed, and low levels of chemical fertilizer and pesticide inputs. Diversity and species richness among crops, rotations, and input levels were compared using 3 indices—the Shannon-Weaver Index, relative diversity, and the Hierarchical Richness Index (HRI). Four carabid species, Cyclotrachelus altemans (Casey), Poecilvs lucublandus Say, Harpalns pensylvanicus (DeGeer), and Bembidion quadrimaculatum L., comprising ≈80% of the total collected, were considered dominant species. When carabid abundance data were grouped by crop, C. altemans was the dominant species in corn and alfalfa and P. lucublandus was dominant in wheat. In soybean plots, C. altemans and P. lucublandus were equally abundant. The relative abundance of H. pensylvanicus was highest in the low-input plots. High values of HRI for carabid diversity and species richness in the managed plots suggested that reduced chemical inputs encouraged greater abundance and diversity of beneficial carabids than were found in the high-input plots without the loss of yield seen in the low-input plots

Diversity and Dominant Species of Ground Beetle Assemblages (Coleoptera: Carabidae) in Crop Rotation and Chemical Input Systems for the Northern Great Plains

Dominant carabid species present in crops and crop rotation sequences commonly used in the northern Great Plains were assessed as an initial step toward the management of carabids as natural control agents. Ground beetle populations were determined by pitfall trapping in 4 crop rotation treatments maintained under high, managed, and low levels of chemical fertilizer and pesticide inputs. Diversity and species richness among crops, rotations, and input levels were compared using 3 indices—the Shannon-Weaver Index, relative diversity, and the Hierarchical Richness Index (HRI). Four carabid species, Cyclotrachelus altemans (Casey), Poecilvs lucublandus Say, Harpalns pensylvanicus (DeGeer), and Bembidion quadrimaculatum L., comprising ≈80% of the total collected, were considered dominant species. When carabid abundance data were grouped by crop, C. altemans was the dominant species in corn and alfalfa and P. lucublandus was dominant in wheat. In soybean plots, C. altemans and P. lucublandus were equally abundant. The relative abundance of H. pensylvanicus was highest in the low-input plots. High values of HRI for carabid diversity and species richness in the managed plots suggested that reduced chemical inputs encouraged greater abundance and diversity of beneficial carabids than were found in the high-input plots without the loss of yield seen in the low-input plots

Sampling Weed Spatial Variability on a Fieldwide Scale

Site-specific weed management recommendations require knowledge of weed species, density, and location in the field. This study compared several sampling techniques to estimate weed density and distribution in two 65-ha no-till Zea mays–Glycine max rotation fields in eastern South Dakota. The most common weeds (Setaria viridis, Setaria glauca, Cirsium arvense, Ambrosia artemisiifolia, and Polygonum pensylvanicum) were counted by species in 0.1-m2 areas on a 15- by 30-m (1,352 points in each field) or 30- by 30-m (676 points in each field) grid pattern, and points were georeferenced and data spatially analyzed. Using different sampling approaches, weed populations were estimated by resampling the original data set. The average density for each technique was calculated and compared with the average field density calculated from the all-point data. All weeds had skewed population distributions with more than 60% of sampling points lacking the specific weed, but very high densities (i.e., \u3e 100 plants m−2) were also observed. More than 300 random samples were required to estimate densities within 20% of the all-point means about 60% of the time. Sampling requirement increased as average density decreased. The W pattern produced average species densities that often were similar to the field averages, but information on patch location was absent. Weed counts taken on the 15- by 30-m grid were dependent spatially and weed contour maps were developed. Kriged maps presented both density and location of weed patches and could be used to establish management zones. However, grid-sampling production fields on a small enough scale to obtain spatially dependent data may have limited usefulness because of time, cost, and labor constraints

Corn and Soil Fertility Responses to Crop Rotation with Low, Medium, or High Inputs

Corn (Zea mays L.) grown in annual rotation with soybean [Glycine max (L.) Merr.] has greater mineral nutrient accumulation and higher yields than corn grown in monoculture. This study was conducted to determine how crop rotation (continuous corn vs. corn rotated with soybean) with different input levels (tillage, herbicide, insecticide, and fertilizer rates varied to achieve high, intermediate, and low treatments) affected corn shoot dry weight, mineral nutrient (N, P, K, Ca, Mg, Cu, Fe, Mn, and Zn) composition at tasseling, pregrowing-season soil fertility (pH, organic matter, NO−3-N, P, K, and total N), and grain yield on a Vienna loam (fine-loamy, mixed Udic Haploboroll) near Brookings, SD. Crop rotation increased total soil N and NO−3-N but decreased P when compared with continuous corn. The high input treatment resulted in higher soil NO−3-N levels than either the intermediate or low input treatments. Rotation with intermediate input increased corn shoot dry weight and P, K, and Ca accumulation compared with continuous corn with intermediate input. Grain yield responded differently to input levels within the two rotations. Corn yield following soybean was 32% greater than for continuous corn with intermediate inputs, but with high input levels there was no difference between rotation treatments. These results suggest that the level of inputs provided for com can affect the crop rotation response