Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 30, 1995
Publication Date: N/A
Interpretive Summary: Grasshoppers are very serious pests of both rangelands and small grain crops, like wheat, throughout the drier portions of the 17 western United States. We conducted a three-year study, during 1988-1990, to examine differences or similarities in the grasshopper communities found at winter wheat borders and adjacent rangeland. We found that during a very dry year (1988), when rangeland forage dried up early in the summer, three major grasshopper pest species tended to migrate from rangeland into winter wheat fields. During more normal years (1989 and 1990) we did not observe significant migration from rangeland to crops, probably because of the availability of suitable forage throughout the summer season. Our results are being used to develop Integrated Pest Management tactics which will help producers monitor rangeland adjacent to crops such as wheat and to better assess if and when to employ an appropriate management strategy.
Comparison of grasshopper density estimates between range and winter wheat taken at weekly sample intervals resulted in the following conclusions. At four study sites, there were significant seasonal shifts in density estimates of M. sanguinipes, M. bivittatus, and M. packardii between the winter wheat and adjacent rangeland suggesting that these species dispersed between habitats. At five study sites such shifts in density did not occur suggesting that no dispersal occurred or it was not detectable at these sites using the sampling methods of this study. The grasshopper densities at these sites were quite low when compared to those of 1985, 1986, and 1987, during an outbreak in Montana, U.S.A. Shifts in seasonal density estimates between habitats may be due to specific environmental and population dynamic factors which are correlated to the dispersal of grasshoppers which are presently unknown. This study quantifies shift in density estimates between winter wheat and adjacent rangeland and also suggests that these shifts are due to dispersal between habitats. Understanding the factors correlated with temporal density estimate shifts between habitats by grasshopper species shared by crops and adjacent rangeland is essential if pest managers are going to make control recommendations proactively before grasshopper populations exceed an economic injury level in crops.