Jerome A. Onsager

Suppression of grasshoppers in the Great Plains through grazing management.

It was hypothesized that grazing management could mitigate grasshopper outbreaks on native rangeland in the northern Great Plains. Key practices would require deliberate variation in timing and intensity of grazing events, preservation of canopy during critical periods of grasshopper development, and reductions in areas of bare soil. The twice-over rotational grazing system appeared compatible with those requirements. Grasshopper population trends were monitored during 1993-1995 and 1997-1998 on commercial native rangeland under twice-over rotational grazing vs traditional season-long grazing. A ubiquitous pest grasshopper, Melanoplus sanguinipes (Fabricius), occurred at every sample site during each year in numbers sufficient to provide life history parameters for comparison between treatments. Under rotational grazing, the nymphs developed significantly slower and their stage-specific survival rates were significantly lower and less variable. Consequently, significantly fewer adults were produced significantly later in the season under rotational grazing. Seasonal presence of all grasshopper species combined averaged 3.3X higher under season-long grazing than under rotational grazing. Local outbreaks that generated 18 and 27 adult grasshoppers per m2 under season-long grazing in 1997 and 1998, respectively, did not occur under rotational grazing. The outbreaks consumed 91% and 168%, respectively, as much forage as had been allocated for livestock, as opposed to 10% and 23%, respectively, under rotational grazing. Of 9 important grasshopper species, none were signiflcantly more abundant at rotational sites than at season-long sites. Three species that were primary contributors to outbreaks under season-long grazing remained innocuous under rotational grazing. It therefore appears that outbreak suppression through grazing management is feasible in the northern Great Plains.

Infection of the corn earworm, Heliothis zea, with Nosema acridophagus and Nosema cuneatum from grasshoppers: Relative virulence and production of spores

Abstract Per os inoculations of 4- to 6-day-old larvae of the corn earworm, Heliothis zea, with suspensions containing 106 spores of Nosema acridophagus or 104, 105, and 106 spores of Nosema cuneatum retarded the growth and development of the larvae. Migratory grasshoppers, Melanoplus sanguinipes, inoculated with N. acridophagus produced fewer spores than similarly inoculated corn earworms, but spore production was similar in these insects when they were inoculated with N. cuneatum. Standard bioassay procedures showed that spores of both microsporidians were some-what more virulent when they were produced in corn earworms than when they were produced in grasshoppers. Spores of these microsporidians might be produced more efficiently in corn earworm larvae than in grasshoppers.

Forage losses caused by the grasshopper Aulocara elliotti on shortgrass rangeland.

Highlight: A field-cage study was conducted in 1973 and 1974 to determine the amount of forage (mainly grasses) destroyed by different population densities of the grasshopper Aulocara elliotti. The amount offorage consumed during the third instar and through the adult stage averaged 34.5 mg offorage per grasshopper per day. Thus, an estimated loss of 23.1 lb offorage per acre will resultfrom a density of one Aulocara/m2 if the grasshopper lives for 75 days (45 days as a nymph and 30 days as an adult). Based on total available forage (standing dead and new growth), a 63% forage loss was recorded in 1973 at one site and losses of 26% and 29% at two sites in 1974 resulting from about 20 grasshoppers/iM2. Severe grazing by grasshoppers also resulted in reduced production offorage during the subsequent (1974) season.

Object-oriented simulation model of rangeland grasshopper population dynamics

An object-oriented simulation model of range land grasshopper population dynamics is under development. Individual objects in the model are aggregated to the landscape level. The model can simulate a community of any number of grasshopper species acting autonomously. In addition, spatial and temporal dynamics are easily included using object-oriented programming techniques.<<ETX>>

A method for estimating economic injury levels for control of rangeland grasshoppers with malathion and carbaryl.

A theoretical “average” rangeland grasshopper weighs 81.6 mg (dry weight) in the adult stage and consumes 9,22, and 53 mg of forage/day in the 4th instar, 5th instar, and adult stages, respectively. Criteria for a computer program are presented whereby grazing pressure from grasshopper infestations can be predicted as a function of initial density and normal daily rate of survival. The benefits of a contemplated control measure may then be estimated through appropriate adjustment of the survival rate. By assigning dollar values to the worth of forage and cost of treatment, the lowest infestation that will justify control measures can be determined. The technique is demonstrated for 2 effective but dissimilar insecticides, malathion and carbaryl. By using actual treatment costs for 1981 control programs and by assuming that an AUM (364 kg of forage) saved from destruction by grasshoppers

Effects of Dipterous Parasitoids on Reproduction of Melanoplus sanguinipes (Orthoptera: Acrididae)

Densities of M. sanguinipes were estimated during spring and summer 1985 in two pastures (LI and HI) of crested wheatgrass. On each sampling date, adult females were collected and brought to the laboratory. Specimens were dissected to check for parasitoids and to determine the status of ovarian development. The parasitoids recorded were Diptera of the following species: Blaesoxipha reversa, B. hunteri, Sarcophaaa kellyi, S. opifora, Neorhynchocephalus sackenii, and Acridomyia canadensis. These parasitoids showed a complete temporal coincidence with adult M. sanguinipes populations. Observations suggest that when the female was parasitized at or before the beginning of vitellogenesis, the parasitoid probably prevented any egg development. Parasitism of females that had advanced egg development or eggs in the oviduct resulted in a high proportion of egg resorption (59%). Mathematical techniques were developed to estimate the proportion of mortality that was attributable to parasitoids, as well as absolute numbers of adult female grasshoppers that did or did not become parasitized. The estimated limits for genera- tional parasitism (GP) for all females were 15.5% to 15.8% for HI and 28.6% to 30.1% for LI. These results suggest that estimates of GP were not strongly affected by the precise moment when parasitism occurred. Diptera parasitoids are natural enemies of grasshopper populations (Greathead 1963, Rees 1973, York and Prescott 1952). The effect of such parasitism on survival, fecundity, and egg viability of individual Melanoplus sanguinipes (F.) in cages has been reported by Prescott (1960) and Rees (1986). However, the impact of parasitism on unconfined populations of grass- hoppers has not been extensively quantified. Most insect parasitoid studies use the percentage of parasit- ism observed in samples as an index of the impact of parasites as mortality factors in the host population. However, phenolo- gies of parasites and hosts might influence these percentages, making such values poor estimators of generational parasitoid affect (Van Driesche 1983, Van Driesche et al. 1991). Indeed, more detailed studies about host and parasitoid phenologies during the season are needed in order to improve the evalua- tion of parasitism. Phenologies of parasitoids and hosts were observed in this study, as well as the loss of host population oviposition poten- tial due to the effect of parasitoids. The objective was to better describe the impact of Diptera parasitism on M. sanguinipes survival and egg production.

A sequential sampling plan for classifying infestations of southern potato wireworm

A plan is proposed whereby 1 to 3 hours of sampling will usually determine whether measures for control of the southern potato wireworm,Conoderus falli Lane, are warranted. This pest is potentially serious but does not consistently occur in sufficient numbers to cause economic injury to potatoes.

Relative efficiency of three methods for chemical control of Pacific coast wireworms in potatoes

Data from six experiments with registered, nonpersistent chemical compounds for control of Pacific coast wireworm (Limonius canus Le-Conte) were combined to elucidate the relative efficiency of three types of treatments. The treatments were soil fumigation and band or broadcast applications of granular organophosphorus insecticides.Band treatments gave less effective and more variable control than broadcast treatments. Fumigation treatments were more effective than, and about equally as variable as, broadcast treatments. All treatments became progressively less effective and less dependable as the population of wireworms increased.It was not economical to treat infestations of less than 0.12 wireworms/ft2. Band treatments were usually adequate for populations up to 0.4/ft2 and broadcast treatments for populations up to 1.6/ft2. However, it was considered most economical to broadcast for infestations between 0.15 and 0.7/ft2. For heavier infestations, either fumigation or a combination of treatments appeared prudent. Because all treatments performed rather inconsistently, precautions to avoid underestimating an infestation are justified.ResumenLos resultados de seis experimentos con compuestos químicos no persistentes para controlar el gusano alambre de la Costa del Pacífico (Limonius canus LeConte) se combinaron para elucidar la eficiencia relativa de tres tratamientos diferentes. Los tratamientos comprendieron fumigación de suelo y aplicaciones en banda y al voleo de insecticidas organofosfóricos.Los tratamientos en banda resultaron menos efectivos y más variables que los al voleo. Las fumigaciones resultaron ser más efectivas y tan variables como las aplicaciones al voleo. Todos los tratamientos se tornaron progresivamente menos efectivos y de confiar a medida que la población de gusanos alambre se incrementó.No resultó económico tratar infestaciones menores que 0,12 gusanos alambre/pie2. Los tratamientos en banda resultaron en general adecuados para poblaciones de hasta 0,4/pie2 y los al voleo para aquéllas de hasta 1,6/pie2. Sin embarago, las aplicaciones al voleo se consideran de máxima economía en infestaciones que fluctúen entre 0,15 y 0,7/pie2. Infestaciones más densas requerirían fumigaciones o una combinación de tratamientos. Por cuanto todos los tratamientos resultaron más bien inconsistentes se justifica ejercer precaución a fin de evitar subestimaciones de la densidad de infestación.