Spittlebug eggs: comparison of sampling efficiency of sample units of different sizes

Abstract

The sampling efficiency of three sample units was compared to determine spittlebug egg densities in pastures of Brachiaria decumbens Stapf. To obtain the same level of precision, the total pasture area to be examined increased by 1.5 times when size of the sample unit was increased from 75 to 150 cm², and by 2.5 times when it was increased to 225 cm² . Using the 75cm² unit, the number of samples necessary for 10%, 15% and 20% levels of precision were estimated to be 170, 82 and 48, respectively. The distribution pattern of egg counts per 75 cm² of the pasture, fitted the negative binomial series. A study of sampling variation within 1 ha pastures, showed that differences between blocks, or plots within blocks were significant only in about 20% instances. Nevertheless, choosing of well-distributed sampling sites within the sampling area was suggested.