Variability in Rangeland Grasshopper (Orthoptera: Acrididae) Counts When Using the Standard, Visualized-Sampling Method
Academic Article
Overview
Identity
Additional Document Info
Other
View All
Overview
abstract
Two studies were conducted near Guernsey, WY, to investigate intersampler variability in grasshopper counts when using the standard visualized 0.1-m2 sampling method. This method is commonly used by researchers and pest managers. The 1st study involved comparing grasshopper counts of samples from 3 interest groups: (1) ranches, (2) pest management practitioners (USDA-APHIS-PPQ personnel), and (3) pest management educators [university personnel]). Results indicated that estimates of grasshopper densities made by individuals in the rancher interest group were much greater than densities estimated by individuals in either the pest management practitioner or pest management educator groups. In addition, there were significant differences among samplers within interest groups. The 2nd study, designed to investigate differences between all samplers in the pest management practitioner and pest management educator groups, showed that significant differences occurred between the counts of samplers in areas containing relatively high grasshopper densities, but not between counts of samplers in areas that harbored 13 grasshoppers per square meter. Some samplers estimates of grasshopper density were inconsistent between 2 areas of relatively high grasshopper density. An influence of increasing sampling experience on decreasing average grasshopper counts existed over both years and all areas of the study. This was effectively corrected by using a binomial sampling model to adjust the average grasshopper counts. However, use of this model did not remove the much stronger differences between samplers. The highly variable grasshopper counts would have led to management errors in 3 of 4 sampled areas surveyed in the 2nd study. Given these results, we suggest that modifications of the visualized 0.1-m2 sampling method be made or perhaps some other sampling method be used to estimate grasshopper densities on western rangelands.
