David E. Legg

Arthropod Prey‐Predator Ratios in a Sagebrush Habitat: Methodological and Ecological Implications

A 3-yr study of arthropod prey-predator ratios, based on species richness and density, was conducted in undisturbed and in intensively managed sagebrush habitats in southeastern Wyoming. Using simulated data sets, Bartletts regression generated sig- nificantly more accurate prey-predator ratios than either simple ratios or ordinary least squares, so Bartletts regression was used for analysis of field data. Both richness and density ratios were generally constant across taxonomic groups (insects, arachnids, and all arthro- pods) in both undisturbed and managed habitats. Prey-predator richness ratios ranged from 1.18 to 2.36 and were considered temporally and spatially constant in undisturbed habitats. The more sensitive density ratios ranged from 2.23 to 7.77, and showed significant variation in time and space. Herbicide application significantly decreased the prey-predator richness ratios in the treatment year, but the ratios increased the following year. Mowing also decreased richness ratios, but the changes were not significant. Although spatial and temporal heterogeneity prevented determination of valid control for assessing the impact of disturbances on most density ratios, the management practices appeared to have in- creased prey-predator ratios in the treatment and posttreatment years.

Simulated Predictions of Insect Phenological Events Made by Using Mean and Median Functional Lower Developmental Thresholds

Abstract A computer-simulated study was conducted to determine whether mean or median functional lower developmental thresholds and required degree-days were superior for predicting the dates on which insect phenological events occurred. In addition, these simulations allowed us to determine if the type of year (weatherwise) influenced those predictions. Results indicated that when median functional lower developmental thresholds and required degree-days were used their predictions were closer to the dates on which the phenological events occurred than were predictions that were made using mean thresholds and required degree-days. Also, the predictions of phenological events made when using median functional lower developmental thresholds and required degree-days were not strongly influenced by the type of year. However, the influence of type of year was quite strong when predictions were made when using mean thresholds and required degree-days. The variability in predictions that were made when using median functional lower developmental thresholds and required degree-days was greater than the variability in predictions that were made when using mean thresholds and required degree days. However, the increased variability was caused by many predictions being closer to, rather than farther from, the actual dates on which the phenological events occurred. Based on these findings, we suggest that median functional lower developmental thresholds, along with median required degree-days, be considered for use when predicting insect phenological events in the field.

Endocoprid Activity of Aphodius fossor (Coleoptera: Scarabaeidae) Related to Bovine Dung Decomposition in a Mixed Grass Prairie

Aphodius fossor (L.) (Coleoptera: Scarabaeidae), a common endocoprid dung beetle in southeastern Wyoming, may have a survival strategy to maintain dung pad integrity and moisture crucial to larval survival in an arid climate (annual precipitation <30 cm). Typically, A. fossor seems to contribute little to dung pad decomposition, because inhabited dung pads seem to be intact and weigh approximately the same as uninhabited pads, even after 1 yr on pasture. To assess the role of A. fossor in dung pad decomposition and nutrient recycling, artificially formed bovine dung pads were inoculated with five pairs of adult A. fossor. After 40 d, A. fossor activity had no measurable effect on external surface area or moisture retention within the dung pad cores. Pads inhabited by A. fossor weighed significantly more than did control pads on most weigh dates of the experiment, possibly because of incorporation of soil particles at the dung/soil interface. Externally, A. fossor-inhabited dung pads seemed intact; however extensive tunneling was evident throughout the core of the pad leaving an intact, protective crust. A. fossor activity increased microbial biomass carbon in the soil beneath the dung pad. Levels of total nitrogen (N) and carbon (C) decreased in the pads but increased in soil beneath the pads. Dung in the core and in the crust of pads with A. fossor had significantly less total N than pads with no beetles and total C was significantly lower in the crust.

Changes in non-target arthropod populations following application of liquid bait formulations of insecticides for control of rangeland grasshoppers

Abstract This study was undertaken to determine the non-target impacts of rangeland grasshopper control using liquid bait formulations of insecticides (canola and corn oil as carriers of carbaryl, diflubenzuron, and malathion). The research was conducted on native rangeland in Wyoming under drought conditions. Three collection methods (pitfall traps, yellow sticky cards, and sweep nets) were used to estimate non-target arthropod densities. The formulated insecticides were applied according to the protocol of reduced agent-area treatments, an application method designed to reduce economic and environmental costs by applying insecticides at low rates with incomplete coverage via alternating treated and untreated swaths). Canola and corn oils are vegetable oils high in linolenic and linoleic acids which function as attractants and phagostimulants for many species of grasshoppers. Crop oil is a biologically inert paraffin-based petroleum product that served as a control. Although all treatments markedly reduced grasshopper population densities, non-target populations were nominally affected. There were no consistent, significant differences in the responses of non-target populations to treatments with the liquid baits (canola and corn oil carriers) relative to those observed with the standard carrier (crop oil). Only one taxonomic group (Formicidae) showed a significant negative response to treatment relative to untreated controls. Logistical and ecological factors associated with grasshopper control methods may account for the nominal effects on non-target taxa. Sweep net and sticky trap sampling were more sensitive to treatment effects and time-by-treatment interactions. Temporal changes in population densities may have made treatment effects difficult to distinguish in several taxonomic groups.

Topsoil Depth Effects on Reclaimed Coal Mine and Native Area Vegetation in Northeastern Wyoming

Abstract Mandated uniform topsoil replacement may hinder or prevent compliance with reclamation bond release standards such as canopy cover, aboveground production, shrub density, and diversity. This investigation was conducted at a coal mine in northeastern Wyoming in order to evaluate the relationship between variable topsoil replacement depths of 15, 30, and 56 cm and short-term revegetation success. Vegetation variables of total cover, total vegetation canopy cover, total number of species, and average number of species (based on cover sampling) were determined on both reclaimed and 2 native reference areas (Upland Grass and Breaks Grass) during 2000, 2001, and 2002, with aboveground production being measured in 2002. The highest total number of species encountered based on canopy cover and aboveground production sampling was in the 30-cm reclaimed treatment, many of which were desirable seeded and volunteer perennial grasses and forbs. In 2001, total vegetation cover on the 56-cm reclaimed treatment was significantly greater than on the 15-cm treatment. Comparison of the current study area to a 1991 reclaimed site indicated a consistent general pattern of species establishment. Aboveground production was also higher in the current reclaimed area than in the native reference areas, while total cover and total vegetation cover were lower. Shannon–Wiener H′ values, based on absolute total vegetation canopy cover, were greater in the 30-cm reclaimed treatment; however, a majority of diversity indices indicated that the Breaks Grass native reference area was more diverse than either Upland Grass or Reclaimed sites. From observations made at the North Antelope/Rochelle Mine, a mosaic of different topsoil depths, including the shallow 15- and 30-cm depths as well as the mandated 56-cm depth, creates the broadest range of vegetation response under a standard regime of revegetation practices. Thus, the capacity to replace different thickness of topsoil should be a reclamation practice available to mine operators.

Economic impact and management of verticillium wilt on irrigated alfalfa hay production in Wyoming

Loss in irrigated alfalfa (Medicago sativa) attributable to Verticillium wilt (caused by Verticillium albo-atrum) was determined by comparing yields of resistant and susceptible cultivars grown in the presence of Verticillium wilt. This loss, in combination with the estimated number of hectares infested with V. albo-atrum and planted to susceptible cultivars, was used to calculate the economic impact of Verticillium wilt on alfalfa hay production. Test plots were established on 13 May 1982 near Dayton, WY. Verticillium wilt was first detected in the test plots before the third harvest in 1984(.)

Influence of variable topsoil replacement depths on soil chemical parameters within a coal mine in northeastern Wyoming, USA

Uniform topsoil replacement depths on coal mine reclaimed areas have been mandated by USA federal and state regulations; however, soils of the premine landscape are not naturally uniform in depth and vary in physical, chemical, and biological characteristics. In addition, uniform topsoil depths may actually hinder the development of diverse reclaimed plant communities. We studied the effect of varying topsoil replacement depth treatments (15, 30, and 56 cm) on soil and backfill pH, electrolytic conductivity (EC), and sodium adsorption ratio (SAR) within a reclaim-ed coal mine study area. Backfill material (also known as spoil) at this site did not possess levels of pH, EC, and SAR that were detrimental to plant growth. There was only a slight reduction in pH, EC, and SAR within the upper 15 cm depth in the reclaimed topsoil treatments with a general increase of EC and SAR in the lower portion of the replaced soil profile. Some downward movement of soluble salts within the reclaimed treatments was evident despite low precipitation. For examples, SAR in the 0–15 cm depth over all reclaimed treatments was lower in 2002 than 2000–2001, and the 0–30 cm portion of the reclaimed soil profile had reduced pH and EC, while the 30–60 cm portion had increased EC and SAR. It is anticipated that soil quality differences in terms of pH, EC, and SAR between topsoil depth treatments will be enhanced with time. Comparison of the reclaimed area to the native reference areas suggested numerous depth differences as a result of homogeneity of the replaced topsoil vs. undisturbed soil profiles.

Structures of benthic insect communities in two southeastern Wyoming (USA) streams: similarities and differences among spatial units at different local scales

Four sites on each of two southeastern Wyoming streams, Medicine Bow River (MBR) and Rock Creek (RC), were investigated during the summer and autumn of 2001 and 2002. This investigation resulted in inventories of benthic insect communities being obtained from these two streams. It also resulted in twelve metrics being calculated from benthic insect communities, and these metrics were compared between two spatial units at different local scales. Of the metrics used, five indicated taxa richness, four indicated relative abundance, two indicated diversity, and one involved a biotic index for organic pollution. More specifically, we used each metric to compare the montane with the plains sub-basin, as well as to compare two distinctly different types of substrates within each of the sub-basins. Also, metrics were compared between the two streams. Results indicated that few differences were observed between naturally-occurring substrates within sub-basins. In addition, few differences were observed between the two streams. In contrast, however, several differences were observed between the montane and plains sub-basins. Such differences were caused from naturally-occurring variations in hydraulic and ecological conditions. These findings suggest that the spatial scale should be carefully considered when selecting metrics for use in monitoring programs that are designed to detect anthropogenic disturbances in lotic systems.

Required number of location-years for estimating functional lower developmental thresholds and required thermal summations of insects: The first emergence of adult Apthona nigriscutis Foudras as an example

Sampling theory was combined with resampling techniques to determine the number of location-years needed for estimating an insects required thermal summation and lower developmental threshold from field-based studies. This was done by analysing 19 location-years of field observations on the first emergence of Apthona nigriscutis Foudras, an important biological control agent of the noxious weed, leafy spurge (Euphorbia esula L.). Results indicated that 5 - 7 location-years were needed to estimate that insects mean required thermal summation and mean lower developmental threshold for predicting first adult emergence. However, if the wish was to estimate the median required thermal summation and median lower developmental threshold for that purpose, then 8 - 11 location-years were needed to obtain acceptable estimates of those parameters. The implications of these and other findings are discussed.

Phenology Models for First Emergence of Adult Apthona nigriscutis (Coleoptera: Chrysomelidae), a Biological Control Agent of Leafy Spurge (Euphorbiaceae)

Abstract A field study was conducted to calculate the functional lower developmental threshold and cumulative required degree-days for first emergence of adult Apthona nigriscutis Foudras, a classical biological control agent of the exotic weed leafy spurge Euphorbia esula L. The study was conducted in Wyoming, Montana, and Minnesota from 1991 through 1999 and made use of the computer program, CALFUN (version 2.0), to estimate the thresholds and required degree-days. Five different methods were used to calculate degree-days, and two kinds of estimates (mean and median) were made for functional lower developmental threshold and required degree-days. In all, 10 phenology models were developed. When we tested these for their accuracy in predicting adult A. nigriscutis first emergence, those that used the historical or sine wave methods for calculating degree-days, and those that used median functional lower developmental thresholds and required degree-days, provided the best predictions. Based on these findings, we suggest using the median functional lower developmental threshold from the historical (−2.56°C) or sine wave (0.14°C) methods to calculate degree-days. Then, when cumulative degree-days approach 1,189.2°C (historical method) or 898.5°C (sine wave method), the onset of adult A. nigriscutis emergence should be imminent. A computer program was written for use by spurge managers so they can easily determine when first emergence of adult A. nigriscutis is likely to begin.