Relationships between temperature and immature developmental rates of apterous and alate Rhopalosiphum padi (L.) were determined in laboratory experiments conducted at constant and fluctuating temperatures. Lower and upper thresholds for development were 5.78 and 25.09 °C, respectively. Studies at fluctuating temperatures which simulated average and extreme low and high temperatures occurring during late-spring in eastern South Dakota were conducted to determine developmental rates and age-specific life table statistics. Developmental rates for cohorts exposed to variable temperatures were similar to expected developmental rates determined from constant temperature studies. Age-specific life table statistics differed among alate and apterous R. padi exposed to identical temperature regimes. On a day time scale, population growth rates of either morph increased with increasing temperature. When data were expressed on a degree-day time scale, population growth rates were similar for cohorts of either morph exposed to low and average temperature regimes. Population growth rates declined for cohorts of both morphs exposed to high temperatures. Equations were provided that estimate age-specific survival and natality for fluctuating temperatures. Stable nymphal instar distributions for apterous R. padi were similar at all temperatures; for populations with stable age structures, approximately 55, 15, 10, 7, and 10% of individuals would be first, second, third, and fourth nymphal instars, and adults, respectively.

The effect of greenbug, Schizaphis graminum (Rondani), infestations on yield components of early- and late-planted spring wheat, Triticum aestivum L., were measured in 2 successive years in eastern South Dakota. Greenbug populations in plots generally increased rapidly and peaked when wheat plants were in boot stage. Populations then began a steady decrease until anthesis, at which time they were near zero. The number of seeds per spikelet and the number of spikelets per square metre were consistently significantly negatively correlated with aphid-days, whereas average seed weight was significantly negatively correlated with aphid-days for only one planting. A linear regression model that included different intercepts for each spring wheat planting and a common slope relating yield to greenbug feeding days (aphid-days) provided a good fit to the data. Based on the model, a loss of 41 kg of grain per hectare is expected for each 100 aphid-days that accumulate per tiller.

Adult corn rootworm beetles, Diabrotica virgifera virgifera LeConte, were maintained at five fluctuating temperature regimens with daily average temperatures of 16.0, 19.5, 23.0, 26.5, and 30.0°C. The mean number of eggs laid per female was greatest (602) at 26.5°C and least (295) at 16.0°C. The median length of life decreased with increasing temperature from 13.8 weeks at 19.5°C to 7.9 weeks at 30.0°C. Parameters were estimated for nonlinear functions relating age-specific fecundity and age-specific survival to physiological age.

A temperature-dependent multiple cohort simulation model was used to predict emergence of western corn rootworms, Diabrotica virgifera virgifera LeConte, from the soil. Hourly 10-cm-depth soil temperatures were used as input to the model. Hourly soil temperatures were predicted from daily minimum and maximum 10-cm-depth soil temperatures using a half-sine-wave approximation, or from minimum and maximum daily 1-m-height air temperatures using a model for predicting soil temperature from air temperature. The mean difference in the number of days between predicted and observed 50% emergence was 0.22 days using soil temperatures and 0.00 days using air temperatures. Linear regressions of predicted versus observed Julian dates of 10, 50, and 90% cumulative beetle emergence from the soil indicated that model predictions were reasonably accurate and precise using both soil and air temperatures.

Similarities in population parameters among aphid species led us to investigate the potential for a single set of parameters that can be used to develop a ‘generic’ sampling plan for multiple small grain aphid species. A weighted average for the slope and intercept used to relate the proportion of infested tillers to the number of aphids per tiller was determined from the data in 15 published reports. These average parameter estimates were used to predict the number of aphids per tiller in 48 wheat fields sampled for four aphid species. The predicted estimates were regressed on the observed estimates with neither slopes nor intercepts differing significantly from one or zero, respectively. Therefore, it appears the single model is adequate for predicting aphid density for the aphid species tested.

Coccinellids are a conspicuous group of aphidophagous predators in maize, Zea mays L., in the Northern Great Plains of the United States. Numerous studies have been conducted on the ecology of coccinellids in maize in North America (Ewert and Chiang 1966a, 1966b; Smith 1971; Foott 1973; Wright and Laing 1980; Corderre and Tourneur 1986; Corderre et al. 1987). However, there have been few long-term surveys of coccinellids in maize. Foott (1973) reported on the abundance of coccinellid species inhabiting maize in eastern Canada over a 4-year period; no surveys of this type have been reported for the Northern Great Plains. We sampled coccinellids in maize fields at three sites in eastern South Dakota for 13 consecutive years to determine the species inhabiting the crop and levels of variation in their abundances among sites and years.

Removal sampling, sweepnet sampling, and visual count sampling conducted while walking at constant velocity through a field were used to sample populations of adults of five coccinellid species in plots established in spring wheat fields, Triticum aestivum L. Estimates of absolute population density obtained from two 20-min removal samples taken from each of six 5- by 5-m sub-plots per plot proved reliable and were used to convert estimates obtained from sweepnet sampling (180 sweeps per plot) and visual counts (36 min per plot walking at 10 m/min) into absolute estimates of population density. Population density estimates obtained by removal sampling were quite precise except for species with low capture efficiencies and low population densities.

Crop plant growth stage influenced the numbers of beetles caught in sweepnet samples and was incorporated in regression models for converting sweepnet catch to absolute density. Values of R2 of regressions ranged from 0.51 to 0.90, depending on species. Visual counts were influenced by temperature and aphid density, and these variables were incorporated in regression models. Values of R2 for regressions relating visual counts to population densities ranged from 0.63 to 0.94, depending on species.

Diaeretiella rapae M'Intosh is a cosmopolitan parasitoid of several pest aphid species in agroecosystems, including the Russian what aphid, Diuraphis noxia (Mordvilko) (Mackauer and Stary 1967). In recent years, D. rapae has been imported into the United States from regions throughout the world for D. noxia classical biological control. Knowledge of the alternative hosts of D. rapae could be useful for identifying ecosystems into which the parasitoid could be released at times when D. noxia is absent. Over 30 aphid species are listed as hosts of D. rapae (Mackauer and Stary 1967). This host list, though comprehensive, is a compilation of information gathered from diverse, mostly unrelated sources, and does not necessarily depict the host range of any particular population. Host range differs among populations of some aphidiid species collected from different regions or from different hosts in the same region (Powell 1986). Thus, published host lists can be misleading if they are the sole source of information used to determine acceptable alternative hosts on which to release prospective candidates in classical biocontrol programs. The purpose of this study was to determine the relative suitability of several aphid species common to agricultural and associated non-agricultural ecosystems in the Great Plains as hosts for this Syrian D. rapae isolate in laboratory no-choice tests.