Grasshopper species composition shifts following a severe rangeland grasshopper outbreak

Authors: Branson, David - Dave

Submitted to: Journal of Orthoptera Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2017
Publication Date: 6/28/2017
Citation: Branson, D.H. 2017. Grasshopper species composition shifts following a severe rangeland grasshopper outbreak. Journal of Orthoptera Research. 26(1):7-10. https://doi.org/10.3897/jor.26.14542.
DOI: https://doi.org/10.3897/jor.26.14542

Interpretive Summary: Grasshoppers are the most economically damaging insect in western U.S. grasslands, with periodic severe outbreaks. Very little is known about shifts in species abundance during and following outbreak periods, as sampling efforts either fail to examine species composition or end when chemical control efforts subside. Grasshopper densities and species composition were sampled at a northern mixed prairie site during and after a severe outbreak, as almost no data exists where grasshopper sampling combined with vegetation sampling occurred during and after a grasshopper outbreak. The dramatic shifts in abundance of the dominant grasshopper species in a severe outbreak, illustrates that species dominance can change rapidly, even for a species that was highly dominant in a severe outbreak. Late-season food availability and thermal conditions seems the most useful correlates to predict both outbreaks and population crashes of later hatching grasshoppers, indicating that managers can use the availability of high quality food availability during the late summer reproductive period to predict outbreak probability. The data can help predict the intensity and decline of grasshopper outbreaks.

Technical Abstract: Little is known about how grasshopper species abundances shift during and following severe outbreaks, as sampling efforts usually end when outbreaks subside. Grasshopper densities, species composition and vegetation have infrequently been sampled during and after a severe outbreak in the western U.S., which is needed to better understand the cause of outbreaks and population declines. In this study, grasshopper densities, species composition and vegetation were monitored at a northern mixed rangeland site from 1999 to 2003 where densities reached 130 per m2 during a severe outbreak. Phoetaliotes nebrascensis comprised 79% of the outbreak in 2000, but declined to 3% by 2003. The dramatic shifts in proportional and actual abundance of P. nebrascensis over a 5 year period illustrate that species dominance can change rapidly, even for a highly dominant outbreak species. The difficulty of fully understanding factors causing shifts in grasshopper populations is illustrated by population declines in all species observed in 2002 and 2003. The data can help predict the intensity and decline of outbreaks and points to the critical importance of long term simultaneous monitoring of grasshopper densities, species composition and vegetation for outbreak prediction.