ESTIMATING DENSITIES OF GRASSHOPPER (ORTHOPTERA, ACRIDIDAE) ASSEMBLAGES - AN EXTENSION OF THE BINOMIAL SAMPLING TECHNIQUE

The effective range of the binomial sampling technique for determining densities of rangeland grasshopper assemblages from the proportion of samples containing grasshoppers was extended by relating the proporti on of 0.1 m(2) samples containing at least 2, 3, 4, or 5 grasshoppers (tally thresholds, t) to grasshopper density. This was done by using t he Poisson probability density function to calculate the probabilities of obtaining 0, 1, 2, 3, and 4 grasshoppers per 0.1 m(2). These proba bilities were then summed and subtracted from 1.0 to yield the theoret ical probabilities corresponding to greater than or equal to 2, 3, 4, or 5 grasshoppers per sample (binomial sampling models). Data collecte d throughout central and eastern Wyoming were used to evaluate the fit of these sampling models. Using tally thresholds of 2, 3, 4, and 5, a nd a maximum-allowable standard error to density ratio of 0.15, grassh opper densities could be reliably estimated up to 38, 63, 84, and 104 grasshoppers per m(2) (32, 53, 70, and 87 per yd(2)).