VARIABILITY IN RANGELAND GRASSHOPPER (ORTHOPTERA, ACRIDIDAE) COUNTS WHEN USING THE STANDARD, VISUALIZED-SAMPLING METHOD

Two studies were conducted near Guernsey, WY, to investigate intersamp ler variability in grasshopper counts when using the standard visualiz ed 0.1-m(2) sampling method. This method is commonly used by researche rs and pest managers. The 1st study involved comparing grasshopper cou nts of samplers from 3 interest groups: (1) ranchers, (2) pest managem ent 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 gro up 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 be tween all samplers in the pest management practitioner and pest manage ment educator groups, showed that significant differences occurred bet ween the counts of samplers in areas containing relatively high grassh opper densities, but not between counts of samplers in areas that harb ored less than or equal to 13 grasshoppers per square meter. Some samp lers' estimates of grasshopper density were inconsistent between 2 are as of relatively high grasshopper density. An influence of increasing sampling experience on decreasing average grasshopper counts existed o ver both years and all areas of the study. This was effectively correc ted by using a binomial sampling model to adjust the average grasshopp er 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 i n the 2nd study. Given these results, we suggest that modifications of the visualized 0.1-m(2) sampling method be made or perhaps some other sampling method be used to estimate grasshopper densities on western rangelands.