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

Interactions Among Western Corn Rootworm (Coleoptera: Chrysomelidae), Yellow Foxtail, and Corn

Field studies at sites with two contrasting soil types investigated effects from the presence of yellow foxtail [Setaria pumila (Poir.) Roem. and Schult.], established in bands parallel to corn rows, on western corn rootworm (Diabrotica virgifera virgifera LeConte) survival, corn root injury, lodging, biomass production, and yield. Results suggested that the presence of foxtail as an alternate host inßuenced the degree and progression of corn rootworm damage and adult emergence in a givenlocality. Rootworm adults emergedlater from foxtail band areas and had smaller head capsule size than did individuals from areas without foxtail, consistent with earlier Þndings that foxtail in the diet of western corn rootworm was a poor nutritional substitute for corn. Lodging was reduced in the presence of yellow foxtail in some cases, but corn stover biomass and yield also were lower. Inßuences, if any, of soil type on rootworm survival were unclear because of differences in planting date between the two sites. Foxtail may function as a buffer to reduce rootworm damage to corn and serves as an alternate host that should be considered in the development of resistance management strategies for transgenic corn modiÞed for rootworm resistance

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

Analysis of Spatial Distribution of Canada Thistle (Cirsium Arvense) in Notill Soybean (Glycine Max)

The nonuniform spatial distribution of weeds across a field landscape complicates sampling and modeling, but allows site specific rather than broadcast management of weed populations. Where weeds are aggregated, densities measured at random locations are not independent, but rather spatially related or autocorrelated. Geostatistical methods were used to describe and map nonrandom distribution and variation of shoot density across ten well established patches of Canada thistle, a perennial weed, in a 65 hectare notillage soybean field in Moody county, South Dakota in 1996. Canada thistle densities were determined by counting the number of shoots present in a 20 by 50 cm (0.1m2 ) rectangle. Shoot densities were recorded at 3.04 m increments in 8 .directions from the center of each patch using adaptive sampling. The boundary of the thistle patch on each axis was arbitrarily defined as having 2 consecutive measurements of 0 shoots per 0.1 m2 . Contour maps of weed densities were generated and overlaid on field topography maps. A contour map was generated to estimate the size and density of each thistle patch. Generally, the highest densities of Canada thistle appear in the center of the patches. Shoot density within the patches declined as the distance from the center of the patch increased. Near infrared images were generated with a digital camera and compared to weed maps produced with ground scouting

Influence of Yellow Foxtail on Corn Growth and Yield

Yellow foxtail [Setaria pumila syn. Setaria glauca (L.) Beauv.] competitive influence on corn (Zea mays L.) growth and yield was investigated at Brookings, South Dakota, and Morris, Minnesota, in 1995 and 1996. Yellow foxtail was seeded at different densities, and at Morris, two levels of nitrogen (N) were applied. Corn biomass measured at V‐6 or V‐8, silking, and harvest and grain yield were correlated negatively to foxtail biomass and density, but the loss differed between years and sites. Nitrogen increased corn growth and decreased yield loss. Defining a single foxtail density or biomass that resulted in a maximum yield loss of 10% was not possible. The most conservative estimate was 3 yellow foxtail plants m−2 or 24 g m−2 of yellow foxtail biomass, but ranged up to 55 plants m−2 and 256 g m−2 when weather conditions and N were optimal

Theoretical Derivation of Stable and Nonisotopic Approaches for Assessing Soil Organic Carbon Turnover

Techniques for measuring soil organic C (SOC) turnover in production fields are needed. The objectives of this study were to propose and test nonisotopic and 13 C stable isotopic techniques for assessing SOC turnover. Based on SOC equilibrium and mass balance relationships, an equation was derived: NHC/SOC initial=[1/(SOC× k NHC)](dSOC/dt)+ k SOC/k NHC, where dSOC/dt is the annual change in SOC, NHC is nonharvested C returned to soil, k SOC is the annual mineralization rate of SOC, and k NHC is the annual mineralization rate of NHC. This equation was used to calculate maintenance rates. An isotopic approach based on simultaneously solving the equations was developed to determine C budgets:(i) SOC retained=[SOC final (Δ soil final− Δ PCR)/(Δ SOCretained− Δ PCR)];(ii) Δ SOC retained= Δ soc initial−[ε ln (SOC retained/SOC initial)],(iii) Δ PCR= Δ NHC−[ε ln (PCR/NHC)]; and (iv) SOC fina

Geostatistical Characterization of the Spatial Distribution of Adult Corn Rootworm (Coleoptera: Chrysomelidae) Emergence

Geostatistical methods were used to characterize spatial variability in western ( Diabrotica virgifera virgifera LeConte) and northern ( Diabrotica barberi Smith & Lawrence) corn rootworm adult emergence patterns. Semivariograms were calculated for adult emergence density of corn rootworm populations in fields of continuous corn and rotated (corn/soybean) corn. Adult emergence densities were generally greater for northern corn rootworms than for western corn rootworms. The spatial structures of the adult rootworm emergence were aggregated as described by spherical spatial models for western corn rootworm and exponential models for northern corn rootworm. Range of spatial dependence varied from 180 to 550 m for western corn rootworm and 172 to 281 m for northern corn rootworm. Semivariograrn models were used to produce contour density maps of adult populations in the fields, based on grid sampling of actual emerging adult populations

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