Suppression of Grasshoppers in the Great Plains through Grazing Management

Abstract

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 m 2 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 significantly 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.

Postembryonic development and food consumption of Dichroplus elongatus Giglio-Tos and Dichroplus maculipennis (Blanchard) (Orhtoptera: Acrididae: Melanoplinae) under laboratory conditions

“…In many situations, they are considered harmful insects because they compete with livestock for available forage (De Wysiecki & Sánchez 1992, Onsager 2000, O´Neill et al 2003, Branson 2008. At high densities, grasshoppers can destroy entire plants or large portions of them, producing not only forage loss, but also decreasing photosynthetic area and inhibiting vegetative reproduction (Hewitt & Onsager 1983).…”

Grasshopper species composition shifts following a severe rangeland grasshopper outbreak

“…Little, if any, data exist where grasshopper densities, species composition and vegetation were sampled during and after a severe outbreak, which is needed to better understand the cause of outbreaks and population declines in the western U.S. (Branson et al 2006, Branson andHaferkamp 2014). Given species differences in food preference and phenology, grasshopper species should differentially respond to abiotic and biotic conditions (Joern 2000, Onsager 2000, Branson et al 2006. In this study, grasshopper densities and species composition were sampled at a northern mixed prairie site during and after a severe outbreak.…”

“…Grasshoppers are often the dominant herbivore in western U.S. grasslands (Belovsky andSlade 2000, Branson et al 2006), with both cyclical regional grasshopper outbreaks and localized outbreaks of 30 to 90 per m 2 in western North America (Nerney and Hamilton 1969, Hewitt and Onsager 1983, Belovsky 2000, Onsager 2000. Despite this, the mechanisms underlying grasshopper outbreak dynamics remain poorly understood (Joern 2000, Onsager 2000, Branson et al 2006, Jonas and Joern 2007, Powell et al 2007, Jonas et al 2015.…”

“…Despite this, the mechanisms underlying grasshopper outbreak dynamics remain poorly understood (Joern 2000, Onsager 2000, Branson et al 2006, Jonas and Joern 2007, Powell et al 2007, Jonas et al 2015. Even less is known about shifts in the relative abundance of species during and following outbreak periods, as sampling efforts either fail to monitor species composition or end when outbreaks or chemical control efforts subside (Onsager 2000).…”

“…Despite this, the mechanisms underlying grasshopper outbreak dynamics remain poorly understood (Joern 2000, Onsager 2000, Branson et al 2006, Jonas and Joern 2007, Powell et al 2007, Jonas et al 2015. Even less is known about shifts in the relative abundance of species during and following outbreak periods, as sampling efforts either fail to monitor species composition or end when outbreaks or chemical control efforts subside (Onsager 2000). Little, if any, data exist where grasshopper densities, species composition and vegetation were sampled during and after a severe outbreak, which is needed to better understand the cause of outbreaks and population declines in the western U.S. (Branson et al 2006, Branson andHaferkamp 2014).…”