How many kilograms of grain per sample unit is big enough? Part II – Simulation of sampling from grain mass with different insect densities and distribution patterns

Abstract

To find representative sampling sizes and units, adult numbers and distributions inside 2700 kg wheat were generated by a computer program. The generated densities of insects with uniform or clumped distributions inside the grain mass were: 0.1, 0.5, 1.0, 2.5, 5.0, and 10.0 adults/kg of grain (A/kg). The grain mass was artificially sampled by the computer program using different combinations of sampling sizes and units. The simulated sampling sizes (number of samples in one sampling set) were: 5, 10, 20, 40, 60, and 100. The simulated sampling units were: 0.5, 1.0, 2.5, 5.0, 7.5, 10.0, and 13.5 kg. When 100 sampling size and a 13.5 kg sampling unit were applied, 50% of the total grain was sampled. Simulation results revealed that more samples were required to detect clumped distributed insects than uniformly distributed insects. Both sample size and unit should be increased with the decrease of insect densities. When insect density was 0.1 A/kg, using 2.5–7.5 kg sampling units would sample less grain mass than that using other sample units to detect insects. To estimate insect density with certain accuracy, sampling size and unit should be properly selected. Using sampling method to estimate insect densities with less than 60% of percent relative variance might not be practical when insect densities were less than 1.0 A/kg. Insect distribution could be incorrectly characterized when sampling size and unit were not chosen correctly. When insect densities were ≤0.5 A/kg, ≥100 sampling sizes with ≥10.0 kg sampling unit were required to accurately characterize insect distribution.